Re: [PATCH v4 2/5] mtd: nand: Qualcomm NAND controller driver

[Brian Norris]

Hi Archit,

On Wed, Aug 19, 2015 at 10:19:03AM +0530, Archit Taneja wrote:
> The Qualcomm NAND controller is found in SoCs like IPQ806x, MSM7xx,
> MDM9x15 series.
> 
> It exists as a sub block inside the IPs EBI2 (External Bus Interface 2)
> and QPIC (Qualcomm Parallel Interface Controller). These IPs provide a
> broader interface for external slow peripheral devices such as LCD and
> NAND/NOR flash memory or SRAM like interfaces.
> 
> We add support for the NAND controller found within EBI2. For the SoCs
> of our interest, we only use the NAND controller within EBI2. Therefore,
> it's safe for us to assume that the NAND controller is a standalone block
> within the SoC.
> 
> The controller supports 512B, 2kB, 4kB and 8kB page 8-bit and 16-bit NAND
> flash devices. It contains a HW ECC block that supports BCH ECC (4, 8 and
> 16 bit correction/step) and RS ECC(4 bit correction/step) that covers main
> and spare data. The controller contains an internal 512 byte page buffer
> to which we read/write via DMA. The EBI2 type NAND controller uses ADM DMA
> for register read/write and data transfers. The controller performs page
> reads and writes at a codeword/step level of 512 bytes. It can support up
> to 2 external chips of different configurations.
> 
> The driver prepares register read and write configuration descriptors for
> each codeword, followed by data descriptors to read or write data from the
> controller's internal buffer. It uses a single ADM DMA channel that we get
> via dmaengine API. The controller requires 2 ADM CRCIs for command and
> data flow control. These are passed via DT.
> 
> The ecc layout used by the controller is syndrome like, but we can't use
> the standard syndrome ecc ops because of several reasons. First, the amount
> of data bytes covered by ecc isn't same in each step. Second, writing to
> free oob space requires us writing to the entire step in which the oob
> lies. This forces us to create our own ecc ops.
> 
> One more difference is how the controller accesses the bad block marker.
> The controller ignores reading the marker when ECC is enabled. ECC needs
> to be explicity disabled to read or write to the bad block marker. For
> this reason, we use the newly created flag NAND_BBT_ACCESS_BBM_RAW to
> read the factory provided bad block markers.
> 
> v4:
> - Shrink submit_descs
> - add desc list node at the end of dma_prep_desc
> - Endianness and warning fixes
> 
> Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>

Where does this sign-off come into play? It's not grouped with yours.
Did Stephen have something to do with v4 only? Also, we typically trim
the change log from the commit message (and place it below the '---' to
do this automatically). Or did you intend for these changelogs to stay
in the git history? I suppose it's not really harmful to keep it in if
you'd like...

> 
> v3:
> - Refactor dma functions for maximum reuse
> - Use dma_slave_confing on stack
> - optimize and clean upempty_page_fixup using memchr_inv
> - ensure portability with dma register reads using le32_* funcs
> - use NAND_USE_BOUNCE_BUFFER instead of doing it ourselves
> - fix handling of return values of dmaengine funcs
> - constify wherever possible
> - Remove dependency on ADM DMA in Kconfig
> - Misc fixes and clean ups
> 
> v2:
> - Use new BBT flag that allows us to read BBM in raw mode
> - reduce memcpy-s in the driver
> - some refactor and clean ups because of above changes
> 
> Reviewed-by: Andy Gross <agross@xxxxxxxxxxxxxx>
> Signed-off-by: Archit Taneja <architt@xxxxxxxxxxxxxx>

Has this driver been tested with drivers/mtd/tests/? Which ones? I'm
particularly interested in oobtest, since you attempted to handle both
ECC and raw OOB.

> ---
>  drivers/mtd/nand/Kconfig      |    7 +
>  drivers/mtd/nand/Makefile     |    1 +
>  drivers/mtd/nand/qcom_nandc.c | 1910 +++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 1918 insertions(+)
>  create mode 100644 drivers/mtd/nand/qcom_nandc.c
> 
> diff --git a/drivers/mtd/nand/Kconfig b/drivers/mtd/nand/Kconfig
> index 5b2806a..6085b8a 100644
> --- a/drivers/mtd/nand/Kconfig
> +++ b/drivers/mtd/nand/Kconfig
> @@ -538,4 +538,11 @@ config MTD_NAND_HISI504
>  	help
>  	  Enables support for NAND controller on Hisilicon SoC Hip04.
>  
> +config MTD_NAND_QCOM
> +	tristate "Support for NAND on QCOM SoCs"
> +	depends on ARCH_QCOM
> +	help
> +	  Enables support for NAND flash chips on SoCs containing the EBI2 NAND
> +	  controller. This controller is found on IPQ806x SoC.
> +
>  endif # MTD_NAND
> diff --git a/drivers/mtd/nand/Makefile b/drivers/mtd/nand/Makefile
> index 1f897ec..87b6a1d 100644
> --- a/drivers/mtd/nand/Makefile
> +++ b/drivers/mtd/nand/Makefile
> @@ -53,5 +53,6 @@ obj-$(CONFIG_MTD_NAND_BCM47XXNFLASH)	+= bcm47xxnflash/
>  obj-$(CONFIG_MTD_NAND_SUNXI)		+= sunxi_nand.o
>  obj-$(CONFIG_MTD_NAND_HISI504)	        += hisi504_nand.o
>  obj-$(CONFIG_MTD_NAND_BRCMNAND)		+= brcmnand/
> +obj-$(CONFIG_MTD_NAND_QCOM)		+= qcom_nandc.o
>  
>  nand-objs := nand_base.o nand_bbt.o nand_timings.o
> diff --git a/drivers/mtd/nand/qcom_nandc.c b/drivers/mtd/nand/qcom_nandc.c
> new file mode 100644
> index 0000000..2337731
> --- /dev/null
> +++ b/drivers/mtd/nand/qcom_nandc.c
> @@ -0,0 +1,1910 @@
> +/*
> + * Copyright (c) 2015, The Linux Foundation. All rights reserved.
> + *
> + * This software is licensed under the terms of the GNU General Public
> + * License version 2, as published by the Free Software Foundation, and
> + * may be copied, distributed, and modified under those terms.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/slab.h>
> +#include <linux/bitops.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/dmaengine.h>
> +#include <linux/module.h>
> +#include <linux/mtd/nand.h>
> +#include <linux/mtd/partitions.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/of_mtd.h>
> +#include <linux/delay.h>
> +
> +/* NANDc reg offsets */
> +#define NAND_FLASH_CMD			0x00
> +#define NAND_ADDR0			0x04
> +#define NAND_ADDR1			0x08
> +#define NAND_FLASH_CHIP_SELECT		0x0c
> +#define NAND_EXEC_CMD			0x10
> +#define NAND_FLASH_STATUS		0x14
> +#define NAND_BUFFER_STATUS		0x18
> +#define NAND_DEV0_CFG0			0x20
> +#define NAND_DEV0_CFG1			0x24
> +#define NAND_DEV0_ECC_CFG		0x28
> +#define NAND_DEV1_ECC_CFG		0x2c
> +#define NAND_DEV1_CFG0			0x30
> +#define NAND_DEV1_CFG1			0x34
> +#define NAND_READ_ID			0x40
> +#define NAND_READ_STATUS		0x44
> +#define NAND_DEV_CMD0			0xa0
> +#define NAND_DEV_CMD1			0xa4
> +#define NAND_DEV_CMD2			0xa8
> +#define NAND_DEV_CMD_VLD		0xac
> +#define SFLASHC_BURST_CFG		0xe0
> +#define NAND_ERASED_CW_DETECT_CFG	0xe8
> +#define NAND_ERASED_CW_DETECT_STATUS	0xec
> +#define NAND_EBI2_ECC_BUF_CFG		0xf0
> +#define FLASH_BUF_ACC			0x100
> +
> +#define NAND_CTRL			0xf00
> +#define NAND_VERSION			0xf08
> +#define NAND_READ_LOCATION_0		0xf20
> +#define NAND_READ_LOCATION_1		0xf24
> +
> +/* dummy register offsets, used by write_reg_dma */
> +#define NAND_DEV_CMD1_RESTORE		0xdead
> +#define NAND_DEV_CMD_VLD_RESTORE	0xbeef
> +
> +/* NAND_FLASH_CMD bits */
> +#define PAGE_ACC			BIT(4)
> +#define LAST_PAGE			BIT(5)
> +
> +/* NAND_FLASH_CHIP_SELECT bits */
> +#define NAND_DEV_SEL			0
> +#define DM_EN				BIT(2)
> +
> +/* NAND_FLASH_STATUS bits */
> +#define FS_OP_ERR			BIT(4)
> +#define FS_READY_BSY_N			BIT(5)
> +#define FS_MPU_ERR			BIT(8)
> +#define FS_DEVICE_STS_ERR		BIT(16)
> +#define FS_DEVICE_WP			BIT(23)
> +
> +/* NAND_BUFFER_STATUS bits */
> +#define BS_UNCORRECTABLE_BIT		BIT(8)
> +#define BS_CORRECTABLE_ERR_MSK		0x1f
> +
> +/* NAND_DEVn_CFG0 bits */
> +#define DISABLE_STATUS_AFTER_WRITE	4
> +#define CW_PER_PAGE			6
> +#define UD_SIZE_BYTES			9
> +#define ECC_PARITY_SIZE_BYTES_RS	19
> +#define SPARE_SIZE_BYTES		23
> +#define NUM_ADDR_CYCLES			27
> +#define STATUS_BFR_READ			30
> +#define SET_RD_MODE_AFTER_STATUS	31
> +
> +/* NAND_DEVn_CFG0 bits */
> +#define DEV0_CFG1_ECC_DISABLE		0
> +#define WIDE_FLASH			1
> +#define NAND_RECOVERY_CYCLES		2
> +#define CS_ACTIVE_BSY			5
> +#define BAD_BLOCK_BYTE_NUM		6
> +#define BAD_BLOCK_IN_SPARE_AREA		16
> +#define WR_RD_BSY_GAP			17
> +#define ENABLE_BCH_ECC			27
> +
> +/* NAND_DEV0_ECC_CFG bits */
> +#define ECC_CFG_ECC_DISABLE		0
> +#define ECC_SW_RESET			1
> +#define ECC_MODE			4
> +#define ECC_PARITY_SIZE_BYTES_BCH	8
> +#define ECC_NUM_DATA_BYTES		16
> +#define ECC_FORCE_CLK_OPEN		30
> +
> +/* NAND_DEV_CMD1 bits */
> +#define READ_ADDR			0
> +
> +/* NAND_DEV_CMD_VLD bits */
> +#define READ_START_VLD			0
> +
> +/* NAND_EBI2_ECC_BUF_CFG bits */
> +#define NUM_STEPS			0
> +
> +/* NAND_ERASED_CW_DETECT_CFG bits */
> +#define ERASED_CW_ECC_MASK		1
> +#define AUTO_DETECT_RES			0
> +#define MASK_ECC			(1 << ERASED_CW_ECC_MASK)
> +#define RESET_ERASED_DET		(1 << AUTO_DETECT_RES)
> +#define ACTIVE_ERASED_DET		(0 << AUTO_DETECT_RES)
> +#define CLR_ERASED_PAGE_DET		(RESET_ERASED_DET | MASK_ECC)
> +#define SET_ERASED_PAGE_DET		(ACTIVE_ERASED_DET | MASK_ECC)
> +
> +/* NAND_ERASED_CW_DETECT_STATUS bits */
> +#define PAGE_ALL_ERASED			BIT(7)
> +#define CODEWORD_ALL_ERASED		BIT(6)
> +#define PAGE_ERASED			BIT(5)
> +#define CODEWORD_ERASED			BIT(4)
> +#define ERASED_PAGE			(PAGE_ALL_ERASED | PAGE_ERASED)
> +#define ERASED_CW			(CODEWORD_ALL_ERASED | CODEWORD_ERASED)
> +
> +/* Version Mask */
> +#define NAND_VERSION_MAJOR_MASK		0xf0000000
> +#define NAND_VERSION_MAJOR_SHIFT	28
> +#define NAND_VERSION_MINOR_MASK		0x0fff0000
> +#define NAND_VERSION_MINOR_SHIFT	16
> +
> +/* NAND OP_CMDs */
> +#define PAGE_READ			0x2
> +#define PAGE_READ_WITH_ECC		0x3
> +#define PAGE_READ_WITH_ECC_SPARE	0x4
> +#define PROGRAM_PAGE			0x6
> +#define PAGE_PROGRAM_WITH_ECC		0x7
> +#define PROGRAM_PAGE_SPARE		0x9
> +#define BLOCK_ERASE			0xa
> +#define FETCH_ID			0xb
> +#define RESET_DEVICE			0xd
> +
> +/*
> + * the NAND controller performs reads/writes with ECC in 516 byte chunks.
> + * the driver calls the chunks 'step' or 'codeword' interchangeably
> + */
> +#define NANDC_STEP_SIZE			512
> +
> +/*
> + * the largest page size we support is 8K, this will have 16 steps/codewords
> + * of 512 bytes each
> + */
> +#define	MAX_NUM_STEPS			(SZ_8K / NANDC_STEP_SIZE)
> +
> +/* we read at most 3 registers per codeword scan */
> +#define MAX_REG_RD			(3 * MAX_NUM_STEPS)
> +
> +/* ECC modes */
> +#define ECC_NONE	BIT(0)
> +#define ECC_RS_4BIT	BIT(1)
> +#define	ECC_BCH_4BIT	BIT(2)
> +#define	ECC_BCH_8BIT	BIT(3)
> +
> +struct desc_info {
> +	struct list_head list;
> +
> +	enum dma_data_direction dir;
> +	struct scatterlist sgl;
> +	struct dma_async_tx_descriptor *dma_desc;
> +};
> +
> +/*
> + * holds the current register values that we want to write. acts as a contiguous
> + * chunk of memory which we use to write the controller registers through DMA.
> + */
> +struct nandc_regs {
> +	__le32 cmd;
> +	__le32 addr0;
> +	__le32 addr1;
> +	__le32 chip_sel;
> +	__le32 exec;
> +
> +	__le32 cfg0;
> +	__le32 cfg1;
> +	__le32 ecc_bch_cfg;
> +
> +	__le32 clrflashstatus;
> +	__le32 clrreadstatus;
> +
> +	__le32 cmd1;
> +	__le32 vld;
> +
> +	__le32 orig_cmd1;
> +	__le32 orig_vld;
> +
> +	__le32 ecc_buf_cfg;
> +};
> +
> +/*
> + * @cmd_crci:			ADM DMA CRCI for command flow control
> + * @data_crci:			ADM DMA CRCI for data flow control
> + * @list:			DMA descriptor list (list of desc_infos)
> + * @data_buffer:		our local DMA buffer for page read/writes,
> + *				used when we can't use the buffer provided
> + *				by upper layers directly
> + * @buf_size/count/start:	markers for chip->read_buf/write_buf functions
> + * @reg_read_buf:		buffer for reading register data via DMA
> + * @reg_read_pos:		marker for data read in reg_read_buf
> + * @cfg0, cfg1, cfg0_raw..:	NANDc register configurations needed for
> + *				ecc/non-ecc mode for the current nand flash
> + *				device
> + * @regs:			a contiguous chunk of memory for DMA register
> + *				writes
> + * @ecc_strength:		4 bit or 8 bit ecc, received via DT
> + * @bus_width:			8 bit or 16 bit NAND bus width, received via DT
> + * @ecc_modes:			supported ECC modes by the current controller,
> + *				initialized via DT match data
> + * @cw_size:			the number of bytes in a single step/codeword
> + *				of a page, consisting of all data, ecc, spare
> + *				and reserved bytes
> + * @cw_data:			the number of bytes within a codeword protected
> + *				by ECC
> + * @bch_enabled:		flag to tell whether BCH or RS ECC mode is used
> + * @status:			value to be returned if NAND_CMD_STATUS command
> + *				is executed
> + */
> +struct qcom_nandc_data {
> +	struct platform_device *pdev;

This field is only set once, but unused?

And it (and several others) aren't documented above.

> +	struct device *dev;
> +
> +	void __iomem *base;
> +	struct resource *res;
> +
> +	struct clk *core_clk;
> +	struct clk *aon_clk;
> +
> +	/* DMA stuff */
> +	struct dma_chan *chan;
> +	struct dma_slave_config	slave_conf;
> +	unsigned int cmd_crci;
> +	unsigned int data_crci;
> +	struct list_head list;
> +
> +	/* MTD stuff */
> +	struct nand_chip chip;
> +	struct mtd_info mtd;
> +
> +	/* local data buffer and markers */
> +	u8		*data_buffer;
> +	int		buf_size;
> +	int		buf_count;
> +	int		buf_start;
> +
> +	/* local buffer to read back registers */
> +	__le32 *reg_read_buf;
> +	int reg_read_pos;
> +
> +	/* required configs */
> +	u32 cfg0, cfg1;
> +	u32 cfg0_raw, cfg1_raw;
> +	u32 ecc_buf_cfg;
> +	u32 ecc_bch_cfg;
> +	u32 clrflashstatus;
> +	u32 clrreadstatus;
> +	u32 sflashc_burst_cfg;
> +	u32 cmd1, vld;
> +
> +	/* register state */
> +	struct nandc_regs *regs;
> +
> +	/* things we get from DT */
> +	int ecc_strength;
> +	int bus_width;
> +
> +	u32 ecc_modes;
> +
> +	/* misc params */
> +	int cw_size;
> +	int cw_data;
> +	bool use_ecc;
> +	bool bch_enabled;
> +	u8 status;
> +	int last_command;
> +};
> +
> +static inline u32 nandc_read(struct qcom_nandc_data *this, int offset)
> +{
> +	return ioread32(this->base + offset);
> +}
> +
> +static inline void nandc_write(struct qcom_nandc_data *this, int offset,
> +			       u32 val)
> +{
> +	iowrite32(val, this->base + offset);
> +}
> +
> +static __le32 *offset_to_nandc_reg(struct nandc_regs *regs, int offset)
> +{
> +	switch (offset) {
> +	case NAND_FLASH_CMD:
> +		return &regs->cmd;
> +	case NAND_ADDR0:
> +		return &regs->addr0;
> +	case NAND_ADDR1:
> +		return &regs->addr1;
> +	case NAND_FLASH_CHIP_SELECT:
> +		return &regs->chip_sel;
> +	case NAND_EXEC_CMD:
> +		return &regs->exec;
> +	case NAND_FLASH_STATUS:
> +		return &regs->clrflashstatus;
> +	case NAND_DEV0_CFG0:
> +		return &regs->cfg0;
> +	case NAND_DEV0_CFG1:
> +		return &regs->cfg1;
> +	case NAND_DEV0_ECC_CFG:
> +		return &regs->ecc_bch_cfg;
> +	case NAND_READ_STATUS:
> +		return &regs->clrreadstatus;
> +	case NAND_DEV_CMD1:
> +		return &regs->cmd1;
> +	case NAND_DEV_CMD1_RESTORE:
> +		return &regs->orig_cmd1;
> +	case NAND_DEV_CMD_VLD:
> +		return &regs->vld;
> +	case NAND_DEV_CMD_VLD_RESTORE:
> +		return &regs->orig_vld;
> +	case NAND_EBI2_ECC_BUF_CFG:
> +		return &regs->ecc_buf_cfg;
> +	default:
> +		return NULL;
> +	}
> +}
> +
> +static void set_nandc_reg(struct qcom_nandc_data *this, int offset, u32 val)
> +{
> +	struct nandc_regs *regs = this->regs;
> +	__le32 *reg;
> +
> +	reg = offset_to_nandc_reg(regs, offset);
> +
> +	if (reg)
> +		*reg = cpu_to_le32(val);
> +}
> +
> +/* helper to configure address register values */
> +static void set_address(struct qcom_nandc_data *this, u16 column, int page)
> +{
> +	struct nand_chip *chip = &this->chip;
> +
> +	if (chip->options & NAND_BUSWIDTH_16)
> +		column >>= 1;
> +
> +	set_nandc_reg(this, NAND_ADDR0, page << 16 | column);
> +	set_nandc_reg(this, NAND_ADDR1, page >> 16 & 0xff);
> +}
> +
> +/*
> + * update_rw_regs:	set up read/write register values, these will be
> + *			written to the NAND controller registers via DMA
> + *
> + * @num_cw:		number of steps for the read/write operation
> + * @read:		read or write operation
> + */
> +static void update_rw_regs(struct qcom_nandc_data *this, int num_cw, bool read)
> +{
> +	u32 cmd, cfg0, cfg1, ecc_bch_cfg;
> +
> +	if (read) {
> +		if (this->use_ecc)
> +			cmd = PAGE_READ_WITH_ECC | PAGE_ACC | LAST_PAGE;
> +		else
> +			cmd = PAGE_READ | PAGE_ACC | LAST_PAGE;
> +	} else {
> +			cmd = PROGRAM_PAGE | PAGE_ACC | LAST_PAGE;
> +	}
> +
> +	if (this->use_ecc) {
> +		cfg0 = (this->cfg0 & ~(7U << CW_PER_PAGE)) |
> +				(num_cw - 1) << CW_PER_PAGE;
> +
> +		cfg1 = this->cfg1;
> +		ecc_bch_cfg = this->ecc_bch_cfg;
> +	} else {
> +		cfg0 = (this->cfg0_raw & ~(7U << CW_PER_PAGE)) |
> +				(num_cw - 1) << CW_PER_PAGE;
> +
> +		cfg1 = this->cfg1_raw;
> +		ecc_bch_cfg = 1 << ECC_CFG_ECC_DISABLE;
> +	}
> +
> +	set_nandc_reg(this, NAND_FLASH_CMD, cmd);
> +	set_nandc_reg(this, NAND_DEV0_CFG0, cfg0);
> +	set_nandc_reg(this, NAND_DEV0_CFG1, cfg1);
> +	set_nandc_reg(this, NAND_DEV0_ECC_CFG, ecc_bch_cfg);
> +	set_nandc_reg(this, NAND_EBI2_ECC_BUF_CFG, this->ecc_buf_cfg);
> +	set_nandc_reg(this, NAND_FLASH_STATUS, this->clrflashstatus);
> +	set_nandc_reg(this, NAND_READ_STATUS, this->clrreadstatus);
> +	set_nandc_reg(this, NAND_EXEC_CMD, 1);
> +}
> +
> +static int prep_dma_desc(struct qcom_nandc_data *this, bool read, int reg_off,
> +			 const void *vaddr, int size, bool flow_control)
> +{
> +	struct desc_info *desc;
> +	struct dma_async_tx_descriptor *dma_desc;
> +	struct scatterlist *sgl;
> +	struct dma_slave_config slave_conf;
> +	enum dma_transfer_direction dir_eng;
> +	int r;
> +
> +	desc = kzalloc(sizeof(*desc), GFP_KERNEL);
> +	if (!desc)
> +		return -ENOMEM;
> +
> +	sgl = &desc->sgl;
> +
> +	sg_init_one(sgl, vaddr, size);
> +
> +	if (read) {
> +		dir_eng = DMA_DEV_TO_MEM;
> +		desc->dir = DMA_FROM_DEVICE;
> +	} else {
> +		dir_eng = DMA_MEM_TO_DEV;
> +		desc->dir = DMA_TO_DEVICE;
> +	}
> +
> +	r = dma_map_sg(this->dev, sgl, 1, desc->dir);
> +	if (r == 0) {
> +		r = -ENOMEM;
> +		goto err;
> +	}
> +
> +	memset(&slave_conf, 0x00, sizeof(slave_conf));
> +
> +	slave_conf.device_fc = flow_control;
> +	if (read) {
> +		slave_conf.src_maxburst = 16;
> +		slave_conf.src_addr = this->res->start + reg_off;
> +		slave_conf.slave_id = this->data_crci;
> +	} else {
> +		slave_conf.dst_maxburst = 16;
> +		slave_conf.dst_addr = this->res->start + reg_off;
> +		slave_conf.slave_id = this->cmd_crci;
> +	}
> +
> +	r = dmaengine_slave_config(this->chan, &slave_conf);
> +	if (r) {
> +		dev_err(this->dev, "failed to configure dma channel\n");
> +		goto err;
> +	}
> +
> +	dma_desc = dmaengine_prep_slave_sg(this->chan, sgl, 1, dir_eng, 0);
> +	if (!dma_desc) {
> +		dev_err(this->dev, "failed to prepare desc\n");
> +		r = -EINVAL;
> +		goto err;
> +	}
> +
> +	desc->dma_desc = dma_desc;
> +
> +	list_add_tail(&desc->list, &this->list);
> +
> +	return 0;
> +err:
> +	kfree(desc);
> +
> +	return r;
> +}
> +
> +/*
> + * read_reg_dma:	prepares a descriptor to read a given number of
> + *			contiguous registers to the reg_read_buf pointer
> + *
> + * @first:		offset of the first register in the contiguous block
> + * @num_regs:		number of registers to read
> + */
> +static int read_reg_dma(struct qcom_nandc_data *this, int first, int num_regs)
> +{
> +	bool flow_control = false;
> +	void *vaddr;
> +	int size;
> +
> +	if (first == NAND_READ_ID || first == NAND_FLASH_STATUS)
> +		flow_control = true;
> +
> +	size = num_regs * sizeof(u32);
> +	vaddr = this->reg_read_buf + this->reg_read_pos;
> +	this->reg_read_pos += num_regs;
> +
> +	return prep_dma_desc(this, true, first, vaddr, size, flow_control);
> +}
> +
> +/*
> + * write_reg_dma:	prepares a descriptor to write a given number of
> + *			contiguous registers
> + *
> + * @first:		offset of the first register in the contiguous block
> + * @num_regs:		number of registers to write
> + */
> +static int write_reg_dma(struct qcom_nandc_data *this, int first, int num_regs)
> +{
> +	bool flow_control = false;
> +	struct nandc_regs *regs = this->regs;
> +	void *vaddr;
> +	int size;
> +
> +	vaddr = offset_to_nandc_reg(regs, first);
> +
> +	if (first == NAND_FLASH_CMD)
> +		flow_control = true;
> +
> +	if (first == NAND_DEV_CMD1_RESTORE)
> +		first = NAND_DEV_CMD1;
> +
> +	if (first == NAND_DEV_CMD_VLD_RESTORE)
> +		first = NAND_DEV_CMD_VLD;
> +
> +	size = num_regs * sizeof(u32);
> +
> +	return prep_dma_desc(this, false, first, vaddr, size, flow_control);
> +}
> +
> +/*
> + * read_data_dma:	prepares a DMA descriptor to transfer data from the
> + *			controller's internal buffer to the buffer 'vaddr'
> + *
> + * @reg_off:		offset within the controller's data buffer
> + * @vaddr:		virtual address of the buffer we want to write to
> + * @size:		DMA transaction size in bytes
> + */
> +static int read_data_dma(struct qcom_nandc_data *this, int reg_off,
> +			 const u8 *vaddr, int size)
> +{
> +	return prep_dma_desc(this, true, reg_off, vaddr, size, false);
> +}
> +
> +/*
> + * write_data_dma:	prepares a DMA descriptor to transfer data from
> + *			'vaddr' to the controller's internal buffer
> + *
> + * @reg_off:		offset within the controller's data buffer
> + * @vaddr:		virtual address of the buffer we want to read from
> + * @size:		DMA transaction size in bytes
> + */
> +static int write_data_dma(struct qcom_nandc_data *this, int reg_off,
> +			  const u8 *vaddr, int size)
> +{
> +	return prep_dma_desc(this, false, reg_off, vaddr, size, false);
> +}
> +
> +/*
> + * helper to prepare dma descriptors to configure registers needed for reading a
> + * codeword/step in a page
> + */
> +static void config_cw_read(struct qcom_nandc_data *this)
> +{
> +	write_reg_dma(this, NAND_FLASH_CMD, 3);
> +	write_reg_dma(this, NAND_DEV0_CFG0, 3);
> +	write_reg_dma(this, NAND_EBI2_ECC_BUF_CFG, 1);
> +
> +	write_reg_dma(this, NAND_EXEC_CMD, 1);
> +
> +	read_reg_dma(this, NAND_FLASH_STATUS, 2);
> +	read_reg_dma(this, NAND_ERASED_CW_DETECT_STATUS, 1);
> +}
> +
> +/*
> + * helpers to prepare dma descriptors used to configure registers needed for
> + * writing a codeword/step in a page
> + */
> +static void config_cw_write_pre(struct qcom_nandc_data *this)
> +{
> +	write_reg_dma(this, NAND_FLASH_CMD, 3);
> +	write_reg_dma(this, NAND_DEV0_CFG0, 3);
> +	write_reg_dma(this, NAND_EBI2_ECC_BUF_CFG, 1);
> +}
> +
> +static void config_cw_write_post(struct qcom_nandc_data *this)
> +{
> +	write_reg_dma(this, NAND_EXEC_CMD, 1);
> +
> +	read_reg_dma(this, NAND_FLASH_STATUS, 1);
> +
> +	write_reg_dma(this, NAND_FLASH_STATUS, 1);
> +	write_reg_dma(this, NAND_READ_STATUS, 1);
> +}
> +
> +/*
> + * the following functions are used within chip->cmdfunc() to perform different
> + * NAND_CMD_* commands
> + */
> +
> +/* sets up descriptors for NAND_CMD_PARAM */
> +static int nandc_param(struct qcom_nandc_data *this)
> +{
> +	/*
> +	 * NAND_CMD_PARAM is called before we know much about the FLASH chip
> +	 * in use. we configure the controller to perform a raw read of 512
> +	 * bytes to read onfi params
> +	 */
> +	set_nandc_reg(this, NAND_FLASH_CMD, PAGE_READ | PAGE_ACC | LAST_PAGE);
> +	set_nandc_reg(this, NAND_ADDR0, 0);
> +	set_nandc_reg(this, NAND_ADDR1, 0);
> +	set_nandc_reg(this, NAND_DEV0_CFG0, 0 << CW_PER_PAGE
> +					| 512 << UD_SIZE_BYTES
> +					| 5 << NUM_ADDR_CYCLES
> +					| 0 << SPARE_SIZE_BYTES);
> +	set_nandc_reg(this, NAND_DEV0_CFG1, 7 << NAND_RECOVERY_CYCLES
> +					| 0 << CS_ACTIVE_BSY
> +					| 17 << BAD_BLOCK_BYTE_NUM
> +					| 1 << BAD_BLOCK_IN_SPARE_AREA
> +					| 2 << WR_RD_BSY_GAP
> +					| 0 << WIDE_FLASH
> +					| 1 << DEV0_CFG1_ECC_DISABLE);
> +	set_nandc_reg(this, NAND_EBI2_ECC_BUF_CFG, 1 << ECC_CFG_ECC_DISABLE);
> +
> +
> +	/* configure CMD1 and VLD for ONFI param probing */
> +	set_nandc_reg(this, NAND_DEV_CMD_VLD,
> +				(this->vld & ~(1 << READ_START_VLD))
> +				| 0 << READ_START_VLD);
> +	set_nandc_reg(this, NAND_DEV_CMD1,
> +				(this->cmd1 & ~(0xFF << READ_ADDR))
> +				| NAND_CMD_PARAM << READ_ADDR);
> +
> +	set_nandc_reg(this, NAND_EXEC_CMD, 1);
> +
> +	set_nandc_reg(this, NAND_DEV_CMD1_RESTORE, this->cmd1);
> +	set_nandc_reg(this, NAND_DEV_CMD_VLD_RESTORE, this->vld);
> +
> +	write_reg_dma(this, NAND_DEV_CMD_VLD, 1);
> +	write_reg_dma(this, NAND_DEV_CMD1, 1);
> +
> +	this->buf_count = 512;
> +	memset(this->data_buffer, 0xff, this->buf_count);
> +
> +	config_cw_read(this);
> +
> +	read_data_dma(this, FLASH_BUF_ACC, this->data_buffer, this->buf_count);
> +
> +	/* restore CMD1 and VLD regs */
> +	write_reg_dma(this, NAND_DEV_CMD1_RESTORE, 1);
> +	write_reg_dma(this, NAND_DEV_CMD_VLD_RESTORE, 1);
> +
> +	return 0;
> +}
> +
> +/* sets up descriptors for NAND_CMD_ERASE1 */
> +static int erase_block(struct qcom_nandc_data *this, int page_addr)
> +{
> +	set_nandc_reg(this, NAND_FLASH_CMD, BLOCK_ERASE | PAGE_ACC | LAST_PAGE);
> +	set_nandc_reg(this, NAND_ADDR0, page_addr);
> +	set_nandc_reg(this, NAND_ADDR1, 0);
> +	set_nandc_reg(this, NAND_DEV0_CFG0,
> +				this->cfg0_raw & ~(7 << CW_PER_PAGE));
> +	set_nandc_reg(this, NAND_DEV0_CFG1, this->cfg1_raw);
> +	set_nandc_reg(this, NAND_EXEC_CMD, 1);
> +	set_nandc_reg(this, NAND_FLASH_STATUS, this->clrflashstatus);
> +	set_nandc_reg(this, NAND_READ_STATUS, this->clrreadstatus);
> +
> +	write_reg_dma(this, NAND_FLASH_CMD, 3);
> +	write_reg_dma(this, NAND_DEV0_CFG0, 2);
> +	write_reg_dma(this, NAND_EXEC_CMD, 1);
> +
> +	read_reg_dma(this, NAND_FLASH_STATUS, 1);
> +
> +	write_reg_dma(this, NAND_FLASH_STATUS, 1);
> +	write_reg_dma(this, NAND_READ_STATUS, 1);
> +
> +	return 0;
> +}
> +
> +/* sets up descriptors for NAND_CMD_READID */
> +static int read_id(struct qcom_nandc_data *this, int column)
> +{
> +	if (column == -1)
> +		return 0;
> +
> +	set_nandc_reg(this, NAND_FLASH_CMD, FETCH_ID);
> +	set_nandc_reg(this, NAND_ADDR0, column);
> +	set_nandc_reg(this, NAND_ADDR1, 0);
> +	set_nandc_reg(this, NAND_FLASH_CHIP_SELECT, DM_EN);
> +	set_nandc_reg(this, NAND_EXEC_CMD, 1);
> +
> +	write_reg_dma(this, NAND_FLASH_CMD, 4);
> +	write_reg_dma(this, NAND_EXEC_CMD, 1);
> +
> +	read_reg_dma(this, NAND_READ_ID, 1);
> +
> +	return 0;
> +}
> +
> +/* sets up descriptors for NAND_CMD_RESET */
> +static int reset(struct qcom_nandc_data *this)
> +{
> +	set_nandc_reg(this, NAND_FLASH_CMD, RESET_DEVICE);
> +	set_nandc_reg(this, NAND_EXEC_CMD, 1);
> +
> +	write_reg_dma(this, NAND_FLASH_CMD, 1);
> +	write_reg_dma(this, NAND_EXEC_CMD, 1);
> +
> +	read_reg_dma(this, NAND_FLASH_STATUS, 1);
> +
> +	return 0;
> +}
> +
> +/* helpers to submit/free our list of dma descriptors */
> +static int submit_descs(struct qcom_nandc_data *this)
> +{
> +	struct desc_info *desc;
> +	dma_cookie_t cookie = 0;
> +
> +	list_for_each_entry(desc, &this->list, list)
> +		cookie = dmaengine_submit(desc->dma_desc);
> +
> +	if (dma_sync_wait(this->chan, cookie) != DMA_COMPLETE)
> +		return -ETIMEDOUT;
> +
> +	return 0;
> +}
> +
> +static void free_descs(struct qcom_nandc_data *this)
> +{
> +	struct desc_info *desc, *n;
> +
> +	list_for_each_entry_safe(desc, n, &this->list, list) {
> +		list_del(&desc->list);
> +		dma_unmap_sg(this->dev, &desc->sgl, 1, desc->dir);
> +		kfree(desc);
> +	}
> +}
> +
> +/* reset the register read buffer for next NAND operation */
> +static void clear_read_regs(struct qcom_nandc_data *this)
> +{
> +	this->reg_read_pos = 0;
> +	memset(this->reg_read_buf, 0, MAX_REG_RD * sizeof(*this->reg_read_buf));
> +}
> +
> +static void pre_command(struct qcom_nandc_data *this, int command)
> +{
> +	this->buf_count = 0;
> +	this->buf_start = 0;
> +	this->use_ecc = false;
> +	this->last_command = command;
> +
> +	clear_read_regs(this);
> +}
> +
> +/*
> + * this is called after NAND_CMD_PAGEPROG and NAND_CMD_ERASE1 to set our
> + * privately maintained status byte, this status byte can be read after
> + * NAND_CMD_STATUS is called
> + */
> +static void parse_erase_write_errors(struct qcom_nandc_data *this, int command)
> +{
> +	struct nand_chip *chip = &this->chip;
> +	struct nand_ecc_ctrl *ecc = &chip->ecc;
> +	int num_cw;
> +	int i;
> +
> +	num_cw = command == NAND_CMD_PAGEPROG ? ecc->steps : 1;
> +
> +	for (i = 0; i < num_cw; i++) {
> +		u32 flash_status = le32_to_cpu(this->reg_read_buf[i]);
> +
> +		if (flash_status & FS_MPU_ERR)
> +			this->status &= ~NAND_STATUS_WP;
> +
> +		if (flash_status & FS_OP_ERR || (i == (num_cw - 1) &&
> +				(flash_status & FS_DEVICE_STS_ERR)))
> +			this->status |= NAND_STATUS_FAIL;
> +	}
> +}
> +
> +static void post_command(struct qcom_nandc_data *this, int command)
> +{
> +	switch (command) {
> +	case NAND_CMD_READID:
> +		memcpy(this->data_buffer, this->reg_read_buf, this->buf_count);
> +		break;
> +	case NAND_CMD_PAGEPROG:
> +	case NAND_CMD_ERASE1:
> +		parse_erase_write_errors(this, command);
> +		break;
> +	default:
> +		break;
> +	}
> +}
> +
> +/*
> + * Implements chip->cmdfunc. It's  only used for a limited set of commands.
> + * The rest of the commands wouldn't be called by upper layers. For example,
> + * NAND_CMD_READOOB would never be called because we have our own versions
> + * of read_oob ops for nand_ecc_ctrl.
> + */
> +static void qcom_nandc_command(struct mtd_info *mtd, unsigned int command,
> +			 int column, int page_addr)
> +{
> +	struct nand_chip *chip = mtd->priv;
> +	struct nand_ecc_ctrl *ecc = &chip->ecc;
> +	struct qcom_nandc_data *this = chip->priv;
> +	bool wait = false;
> +	int r = 0;
> +
> +	pre_command(this, command);
> +
> +	switch (command) {
> +	case NAND_CMD_RESET:
> +		r = reset(this);
> +		wait = true;
> +		break;
> +
> +	case NAND_CMD_READID:
> +		this->buf_count = 4;
> +		r = read_id(this, column);
> +		wait = true;
> +		break;
> +
> +	case NAND_CMD_PARAM:
> +		r = nandc_param(this);
> +		wait = true;
> +		break;
> +
> +	case NAND_CMD_ERASE1:
> +		r = erase_block(this, page_addr);
> +		wait = true;
> +		break;
> +
> +	case NAND_CMD_READ0:
> +		/* we read the entire page for now */
> +		WARN_ON(column != 0);
> +
> +		this->use_ecc = true;
> +		set_address(this, 0, page_addr);
> +		update_rw_regs(this, ecc->steps, true);
> +		break;
> +
> +	case NAND_CMD_SEQIN:
> +		WARN_ON(column != 0);
> +		set_address(this, 0, page_addr);
> +		break;
> +
> +	case NAND_CMD_PAGEPROG:
> +	case NAND_CMD_STATUS:
> +	case NAND_CMD_NONE:
> +	default:
> +		break;
> +	}
> +
> +	if (r) {
> +		dev_err(this->dev, "failure executing command %d\n",
> +			command);
> +		free_descs(this);
> +		return;
> +	}
> +
> +	if (wait) {
> +		r = submit_descs(this);
> +		if (r)
> +			dev_err(this->dev,
> +				"failure submitting descs for command %d\n",
> +				command);
> +	}
> +
> +	free_descs(this);
> +
> +	post_command(this, command);
> +}
> +
> +/*
> + * when using RS ECC, the NAND controller flags an error when reading an
> + * erased page. however, there are special characters at certain offsets when
> + * we read the erased page. we check here if the page is really empty. if so,
> + * we replace the magic characters with 0xffs
> + */

What's the nature of this erased page flagging? Does it only detect
all-0xff pages? What about if the erased page experiences any bitflips?
A lot of drivers have been attempting to handle that case too (which is
becoming more common on modern MLC, and even on SLC), and most of the
times they do it poorly.

See nand_check_erased_ecc_chunk() (in linux-next.git) as an example of a
brute force helper to assist for cases where HW ECC is not sufficient.

> +static bool empty_page_fixup(struct qcom_nandc_data *this, u8 *data_buf)
> +{
> +	struct mtd_info *mtd = &this->mtd;
> +	struct nand_chip *chip = &this->chip;
> +	struct nand_ecc_ctrl *ecc = &chip->ecc;
> +	int cwperpage = ecc->steps;
> +	u8 orig1[MAX_NUM_STEPS], orig2[MAX_NUM_STEPS];
> +	int i, j;
> +
> +	/* if BCH is enabled, HW will take care of detecting erased pages */
> +	if (this->bch_enabled || !this->use_ecc)
> +		return false;
> +
> +	for (i = 0; i < cwperpage; i++) {
> +		u8 *empty1, *empty2;
> +		u32 flash_status = le32_to_cpu(this->reg_read_buf[3 * i]);
> +
> +		/*
> +		 * an erased page flags an error in NAND_FLASH_STATUS, check if
> +		 * the page is erased by looking for 0x54s at offsets 3 and 175
> +		 * from the beginning of each codeword
> +		 */
> +		if (!(flash_status & FS_OP_ERR))
> +			break;
> +
> +		empty1 = &data_buf[3 + i * this->cw_data];
> +		empty2 = &data_buf[175 + i * this->cw_data];
> +
> +		/*
> +		 * if the error wasn't because of an erased page, bail out and
> +		 * and let someone else do the error checking
> +		 */
> +		if ((*empty1 == 0x54 && *empty2 == 0xff) ||
> +				(*empty1 == 0xff && *empty2 == 0x54)) {
> +			orig1[i] = *empty1;
> +			orig2[i] = *empty2;
> +
> +			*empty1 = 0xff;
> +			*empty2 = 0xff;
> +		} else {
> +			break;
> +		}
> +	}
> +
> +	if (i < cwperpage || memchr_inv(data_buf, 0xff, mtd->writesize))
> +		goto not_empty;
> +
> +	/*
> +	 * tell the caller that the page was empty and is fixed up, so that
> +	 * parse_read_errors() doesn't think it's an error
> +	 */
> +	return true;
> +
> +not_empty:
> +	/* restore original values if not empty*/
> +	for (j = 0; j < i; j++) {
> +		data_buf[3 + j * this->cw_data] = orig1[j];
> +		data_buf[175 + j * this->cw_data] = orig2[j];
> +	}
> +
> +	return false;
> +}
> +
> +struct read_stats {
> +	__le32 flash;
> +	__le32 buffer;
> +	__le32 erased_cw;
> +};
> +
> +/*
> + * reads back status registers set by the controller to notify page read
> + * errors. this is equivalent to what 'ecc->correct()' would do.
> + */
> +static int parse_read_errors(struct qcom_nandc_data *this, bool erased_page)
> +{
> +	struct mtd_info *mtd = &this->mtd;
> +	struct nand_chip *chip = &this->chip;
> +	struct nand_ecc_ctrl *ecc = &chip->ecc;
> +	int cwperpage = ecc->steps;
> +	unsigned int max_bitflips = 0;
> +	int i;
> +	struct read_stats *buf;
> +
> +	buf = (struct read_stats *)this->reg_read_buf;
> +	for (i = 0; i < cwperpage; i++, buf++) {
> +		unsigned int stat;
> +		u32 flash, buffer, erased_cw;
> +
> +		flash = le32_to_cpu(buf->flash);
> +		buffer = le32_to_cpu(buf->buffer);
> +		erased_cw = le32_to_cpu(buf->erased_cw);
> +
> +		if (flash & (FS_OP_ERR | FS_MPU_ERR)) {
> +
> +			/* ignore erased codeword errors */
> +			if (this->bch_enabled) {
> +				if ((erased_cw & ERASED_CW) == ERASED_CW)
> +					continue;
> +			} else if (erased_page) {
> +				continue;
> +			}
> +
> +			if (buffer & BS_UNCORRECTABLE_BIT) {
> +				mtd->ecc_stats.failed++;
> +				continue;
> +			}
> +		}
> +
> +		stat = buffer & BS_CORRECTABLE_ERR_MSK;
> +		mtd->ecc_stats.corrected += stat;
> +
> +		max_bitflips = max(max_bitflips, stat);
> +	}
> +
> +	return max_bitflips;
> +}
> +
> +/*
> + * helper to perform the actual page read operation, used by ecc->read_page()
> + * and ecc->read_oob()
> + */
> +static int read_page_low(struct qcom_nandc_data *this, u8 *data_buf,
> +			 u8 *oob_buf)
> +{
> +	struct nand_chip *chip = &this->chip;
> +	struct nand_ecc_ctrl *ecc = &chip->ecc;
> +	int i, r;
> +
> +	/* queue cmd descs for each codeword */
> +	for (i = 0; i < ecc->steps; i++) {
> +		int data_size, oob_size;
> +
> +		if (i == (ecc->steps - 1)) {
> +			data_size = ecc->size - ((ecc->steps - 1) << 2);
> +			oob_size = (ecc->steps << 2) + ecc->bytes;
> +		} else {
> +			data_size = this->cw_data;
> +			oob_size = ecc->bytes;
> +		}
> +
> +		config_cw_read(this);
> +
> +		if (data_buf)
> +			read_data_dma(this, FLASH_BUF_ACC, data_buf, data_size);
> +
> +		if (oob_buf)
> +			read_data_dma(this, FLASH_BUF_ACC + data_size, oob_buf,
> +					oob_size);
> +
> +		if (data_buf)
> +			data_buf += data_size;
> +		if (oob_buf)
> +			oob_buf += oob_size;
> +	}
> +
> +	r = submit_descs(this);
> +	if (r)
> +		dev_err(this->dev, "failure to read page/oob\n");
> +
> +	free_descs(this);
> +
> +	return r;
> +}
> +
> +/*
> + * a helper that copies the last step/codeword of a page (containing free oob)
> + * into our local buffer
> + */
> +static int copy_last_cw(struct qcom_nandc_data *this, bool use_ecc, int page)
> +{
> +	struct nand_chip *chip = &this->chip;
> +	struct nand_ecc_ctrl *ecc = &chip->ecc;
> +	int size;
> +	int r;
> +
> +	clear_read_regs(this);
> +
> +	size = use_ecc ? this->cw_data : this->cw_size;
> +
> +	/* prepare a clean read buffer */
> +	memset(this->data_buffer, 0xff, size);
> +
> +	this->use_ecc = use_ecc;
> +	set_address(this, this->cw_size * (ecc->steps - 1), page);
> +	update_rw_regs(this, 1, true);
> +
> +	config_cw_read(this);
> +
> +	read_data_dma(this, FLASH_BUF_ACC, this->data_buffer, size);
> +
> +	r = submit_descs(this);
> +	if (r)
> +		dev_err(this->dev, "failed to copy last codeword\n");
> +
> +	free_descs(this);
> +
> +	return r;
> +}
> +
> +/* implements ecc->read_page() */
> +static int qcom_nandc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
> +				uint8_t *buf, int oob_required, int page)
> +{
> +	struct qcom_nandc_data *this = chip->priv;
> +	u8 *data_buf, *oob_buf = NULL;
> +	bool erased_page;
> +	int r;
> +
> +	data_buf = buf;
> +	oob_buf = oob_required ? chip->oob_poi : NULL;
> +
> +	r = read_page_low(this, data_buf, oob_buf);
> +	if (r) {
> +		dev_err(this->dev, "failure to read page\n");
> +		return r;
> +	}
> +
> +	erased_page = empty_page_fixup(this, data_buf);
> +
> +	return parse_read_errors(this, erased_page);
> +}
> +
> +/* implements ecc->read_oob() */
> +static int qcom_nandc_read_oob(struct mtd_info *mtd, struct nand_chip *chip,
> +			       int page)
> +{
> +	struct qcom_nandc_data *this = chip->priv;
> +	struct nand_ecc_ctrl *ecc = &chip->ecc;
> +	int r;
> +
> +	clear_read_regs(this);
> +
> +	this->use_ecc = true;
> +	set_address(this, 0, page);
> +	update_rw_regs(this, ecc->steps, true);
> +
> +	r = read_page_low(this, NULL, chip->oob_poi);
> +	if (r)
> +		dev_err(this->dev, "failure to read oob\n");
> +
> +	return r;
> +}
> +
> +/* implements ecc->read_oob_raw(), used to read the bad block marker flag */
> +static int qcom_nandc_read_oob_raw(struct mtd_info *mtd, struct nand_chip *chip,
> +				   int page)
> +{
> +	struct qcom_nandc_data *this = chip->priv;
> +	struct nand_ecc_ctrl *ecc = &chip->ecc;
> +	uint8_t *oob = chip->oob_poi;
> +	int start, length;
> +	int r;
> +
> +	/*
> +	 * configure registers for a raw page read, the address is set to the
> +	 * beginning of the last codeword, we don't care about reading ecc
> +	 * portion of oob, just the free stuff
> +	 */
> +	r = copy_last_cw(this, false, page);
> +	if (r)
> +		return r;
> +
> +	/*
> +	 * reading raw oob has 2 parts, first the bad block byte, then the
> +	 * actual free oob region. perform a memcpy in two steps
> +	 */
> +	start = mtd->writesize - (this->cw_size * (ecc->steps - 1));
> +	length = chip->options & NAND_BUSWIDTH_16 ? 2 : 1;
> +
> +	memcpy(oob, this->data_buffer + start, length);
> +
> +	oob += length;
> +
> +	start = this->cw_data - (ecc->steps << 2) + 1;
> +	length = ecc->steps << 2;
> +
> +	memcpy(oob, this->data_buffer + start, length);
> +
> +	return 0;
> +}
> +
> +/* implements ecc->write_page() */
> +static int qcom_nandc_write_page(struct mtd_info *mtd, struct nand_chip *chip,
> +				 const uint8_t *buf, int oob_required)
> +{
> +	struct qcom_nandc_data *this = chip->priv;
> +	struct nand_ecc_ctrl *ecc = &chip->ecc;
> +	u8 *data_buf, *oob_buf;
> +	int i, r = 0;
> +
> +	clear_read_regs(this);
> +
> +	data_buf = (u8 *) buf;
> +	oob_buf = chip->oob_poi;
> +
> +	this->use_ecc = true;
> +	update_rw_regs(this, ecc->steps, false);
> +
> +	for (i = 0; i < ecc->steps; i++) {
> +		int data_size, oob_size;
> +
> +		if (i == (ecc->steps - 1)) {
> +			data_size = ecc->size - ((ecc->steps - 1) << 2);
> +			oob_size = (ecc->steps << 2) + ecc->bytes;
> +		} else {
> +			data_size = this->cw_data;
> +			oob_size = ecc->bytes;
> +		}
> +
> +		config_cw_write_pre(this);
> +		write_data_dma(this, FLASH_BUF_ACC, data_buf, data_size);
> +
> +		/*
> +		 * we don't really need to write anything to oob for the
> +		 * first n - 1 codewords since these oob regions just
> +		 * contain ecc that's written by the controller itself
> +		 */
> +		if (i == (ecc->steps - 1))
> +			write_data_dma(this, FLASH_BUF_ACC + data_size,
> +					oob_buf, oob_size);
> +		config_cw_write_post(this);
> +
> +		data_buf += data_size;
> +		oob_buf += oob_size;
> +	}
> +
> +	r = submit_descs(this);
> +	if (r)
> +		dev_err(this->dev, "failure to write page\n");
> +
> +	free_descs(this);
> +
> +	return r;
> +}
> +
> +/*
> + * implements ecc->write_oob()
> + *
> + * the NAND controller cannot write only data or only oob within a codeword,
> + * since ecc is calculated for the combined codeword. we first copy the
> + * entire contents for the last codeword(data + oob), replace the old oob
> + * with the new one in chip->oob_poi, and then write the entire codeword.
> + * this read-copy-write operation results in a slight perormance loss.
> + */
> +static int qcom_nandc_write_oob(struct mtd_info *mtd, struct nand_chip *chip,
> +				int page)
> +{
> +	struct qcom_nandc_data *this = chip->priv;
> +	struct nand_ecc_ctrl *ecc = &chip->ecc;
> +	uint8_t *oob = chip->oob_poi;
> +	int free_boff;
> +	int data_size, oob_size;
> +	int r, status = 0;
> +
> +	r = copy_last_cw(this, true, page);
> +	if (r)
> +		return r;
> +
> +	clear_read_regs(this);
> +
> +	/* calculate the data and oob size for the last codeword/step */
> +	data_size = ecc->size - ((ecc->steps - 1) << 2);
> +	oob_size = (ecc->steps << 2) + ecc->bytes;
> +
> +	/*
> +	 * the location of spare data in the oob buffer, we could also use
> +	 * ecc->layout.oobfree here
> +	 */
> +	free_boff = ecc->bytes * (ecc->steps - 1);
> +
> +	/* override new oob content to last codeword */
> +	memcpy(this->data_buffer + data_size, oob + free_boff, oob_size);
> +
> +	this->use_ecc = true;
> +	set_address(this, this->cw_size * (ecc->steps - 1), page);
> +	update_rw_regs(this, 1, false);
> +
> +	config_cw_write_pre(this);
> +	write_data_dma(this, FLASH_BUF_ACC, this->data_buffer,
> +		data_size + oob_size);
> +	config_cw_write_post(this);
> +
> +	r = submit_descs(this);
> +
> +	free_descs(this);
> +
> +	if (r) {
> +		dev_err(this->dev, "failure to write oob\n");
> +		return -EIO;
> +	}
> +
> +	chip->cmdfunc(mtd, NAND_CMD_PAGEPROG, -1, -1);
> +
> +	status = chip->waitfunc(mtd, chip);
> +
> +	return status & NAND_STATUS_FAIL ? -EIO : 0;
> +}
> +
> +/* implements ecc->write_oob_raw(), used to write bad block marker flag */
> +static int qcom_nandc_write_oob_raw(struct mtd_info *mtd,
> +				    struct nand_chip *chip, int page)
> +{
> +	struct qcom_nandc_data *this = chip->priv;
> +	struct nand_ecc_ctrl *ecc = &chip->ecc;
> +	uint8_t *oob = chip->oob_poi;
> +	int start, length;
> +	int r, status = 0;
> +
> +	r = copy_last_cw(this, false, page);
> +	if (r)
> +		return r;
> +
> +	clear_read_regs(this);
> +
> +	/*
> +	 * writing raw oob has 2 parts, first the bad block region, then the
> +	 * actual free region
> +	 */
> +	start = mtd->writesize - (this->cw_size * (ecc->steps - 1));
> +	length = chip->options & NAND_BUSWIDTH_16 ? 2 : 1;
> +
> +	memcpy(this->data_buffer + start, oob, length);
> +
> +	oob += length;
> +
> +	start = this->cw_data - (ecc->steps << 2) + 1;
> +	length = ecc->steps << 2;
> +
> +	memcpy(this->data_buffer + start, oob, length);
> +
> +	/* prepare write */
> +	this->use_ecc = false;
> +	set_address(this, this->cw_size * (ecc->steps - 1), page);
> +	update_rw_regs(this, 1, false);
> +
> +	config_cw_write_pre(this);
> +	write_data_dma(this, FLASH_BUF_ACC, this->data_buffer, this->cw_size);
> +	config_cw_write_post(this);
> +
> +	r = submit_descs(this);
> +
> +	free_descs(this);
> +
> +	if (r) {
> +		dev_err(this->dev, "failure to write updated oob\n");
> +		return -EIO;
> +	}
> +
> +	chip->cmdfunc(mtd, NAND_CMD_PAGEPROG, -1, -1);
> +
> +	status = chip->waitfunc(mtd, chip);
> +
> +	return status & NAND_STATUS_FAIL ? -EIO : 0;
> +}
> +
> +/*
> + * the three functions below implement chip->read_byte(), chip->read_buf()
> + * and chip->write_buf() respectively. these aren't used for
> + * reading/writing page data, they are used for smaller data like reading
> + * id, status etc
> + */
> +static uint8_t qcom_nandc_read_byte(struct mtd_info *mtd)
> +{
> +	struct nand_chip *chip = mtd->priv;
> +	struct qcom_nandc_data *this = chip->priv;
> +	uint8_t *buf = this->data_buffer;
> +	uint8_t ret = 0x0;
> +
> +	if (this->last_command == NAND_CMD_STATUS) {
> +		ret = this->status;
> +
> +		this->status = NAND_STATUS_READY | NAND_STATUS_WP;
> +
> +		return ret;
> +	}
> +
> +	if (this->buf_start < this->buf_count)
> +		ret = buf[this->buf_start++];
> +
> +	return ret;
> +}
> +
> +static void qcom_nandc_read_buf(struct mtd_info *mtd, uint8_t *buf, int len)
> +{
> +	struct nand_chip *chip = mtd->priv;
> +	struct qcom_nandc_data *this = chip->priv;
> +	int real_len = min_t(size_t, len, this->buf_count - this->buf_start);
> +
> +	memcpy(buf, this->data_buffer + this->buf_start, real_len);
> +	this->buf_start += real_len;
> +}
> +
> +static void qcom_nandc_write_buf(struct mtd_info *mtd, const uint8_t *buf,
> +		int len)
> +{
> +	struct nand_chip *chip = mtd->priv;
> +	struct qcom_nandc_data *this = chip->priv;
> +	int real_len = min_t(size_t, len, this->buf_count - this->buf_start);
> +
> +	memcpy(this->data_buffer + this->buf_start, buf, real_len);
> +
> +	this->buf_start += real_len;
> +}
> +
> +/* we support only one external chip for now */
> +static void qcom_nandc_select_chip(struct mtd_info *mtd, int chipnr)
> +{
> +	struct nand_chip *chip = mtd->priv;
> +	struct qcom_nandc_data *this = chip->priv;
> +
> +	if (chipnr <= 0)
> +		return;
> +
> +	dev_warn(this->dev, "invalid chip select\n");
> +}
> +
> +/*
> + * NAND controller page layout info
> + *
> + * |-----------------------|	  |---------------------------------|
> + * |		xx.......xx|	  |		*********xx.......xx|
> + * |	DATA	xx..ECC..xx|	  |	DATA	**SPARE**xx..ECC..xx|
> + * |   (516)	xx.......xx|	  |  (516-n*4)	**(n*4)**xx.......xx|
> + * |		xx.......xx|	  |		*********xx.......xx|
> + * |-----------------------|	  |---------------------------------|
> + *     codeword 1,2..n-1			codeword n
> + *  <---(528/532 Bytes)---->	   <-------(528/532 Bytes)---------->
> + *
> + * n = number of codewords in the page
> + * . = ECC bytes
> + * * = spare bytes
> + * x = unused/reserved bytes
> + *
> + * 2K page: n = 4, spare = 16 bytes
> + * 4K page: n = 8, spare = 32 bytes
> + * 8K page: n = 16, spare = 64 bytes
> + *
> + * the qcom nand controller operates at a sub page/codeword level. each
> + * codeword is 528 and 532 bytes for 4 bit and 8 bit ECC modes respectively.
> + * the number of ECC bytes vary based on the ECC strength and the bus width.
> + *
> + * the first n - 1 codewords contains 516 bytes of user data, the remaining
> + * 12/16 bytes consist of ECC and reserved data. The nth codeword contains
> + * both user data and spare(oobavail) bytes that sum up to 516 bytes.
> + *
> + * the layout described above is used by the controller when the ECC block is
> + * enabled. When we read a page with ECC enabled, the unused/reserved bytes are
> + * skipped and not copied to our internal buffer. therefore, the nand_ecclayout
> + * layouts defined below doesn't consider the positions occupied by the reserved
> + * bytes
> + *
> + * when the ECC block is disabled, one unused byte (or two for 16 bit bus width)
> + * in the last codeword is the position of bad block marker. the bad block
> + * marker cannot be accessed when ECC is enabled.
> + *
> + */
> +
> +/*
> + * Layouts for different page sizes and ecc modes. We skip the eccpos field
> + * since it isn't needed for this driver
> + */
> +
> +/* 2K page, 4 bit ECC */
> +static struct nand_ecclayout layout_oob_64 = {
> +	.eccbytes	= 40,
> +	.oobfree	= {
> +				{ 30, 16 },
> +			  },
> +};
> +
> +/* 4K page, 4 bit ECC, 8/16 bit bus width */
> +static struct nand_ecclayout layout_oob_128 = {
> +	.eccbytes	= 80,
> +	.oobfree	= {
> +				{ 70, 32 },
> +			  },
> +};
> +
> +/* 4K page, 8 bit ECC, 8 bit bus width */
> +static struct nand_ecclayout layout_oob_224_x8 = {
> +	.eccbytes	= 104,
> +	.oobfree	= {
> +				{ 91, 32 },
> +			  },
> +};
> +
> +/* 4K page, 8 bit ECC, 16 bit bus width */
> +static struct nand_ecclayout layout_oob_224_x16 = {
> +	.eccbytes	= 112,
> +	.oobfree	= {
> +				{ 98, 32 },
> +			  },
> +};
> +
> +/* 8K page, 4 bit ECC, 8/16 bit bus width */
> +static struct nand_ecclayout layout_oob_256 = {
> +	.eccbytes	= 160,
> +	.oobfree	= {
> +				{ 151, 64 },
> +			  },
> +};
> +
> +/*
> + * this is called before scan_ident, we do some minimal configurations so
> + * that reading ID and ONFI params work
> + */
> +static void qcom_nandc_pre_init(struct qcom_nandc_data *this)
> +{
> +	/* kill onenand */
> +	nandc_write(this, SFLASHC_BURST_CFG, 0);
> +
> +	/* enable ADM DMA */
> +	nandc_write(this, NAND_FLASH_CHIP_SELECT, DM_EN);
> +
> +	/* save the original values of these registers */
> +	this->cmd1 = nandc_read(this, NAND_DEV_CMD1);
> +	this->vld = nandc_read(this, NAND_DEV_CMD_VLD);
> +
> +	/* initial status value */
> +	this->status = NAND_STATUS_READY | NAND_STATUS_WP;
> +}
> +
> +static int qcom_nandc_ecc_init(struct qcom_nandc_data *this)
> +{
> +	struct mtd_info *mtd = &this->mtd;
> +	struct nand_chip *chip = &this->chip;
> +	struct nand_ecc_ctrl *ecc = &chip->ecc;
> +	int cwperpage;
> +	bool wide_bus;
> +
> +	/* the nand controller fetches codewords/chunks of 512 bytes */
> +	cwperpage = mtd->writesize >> 9;
> +
> +	ecc->strength = this->ecc_strength;
> +
> +	wide_bus = chip->options & NAND_BUSWIDTH_16 ? true : false;
> +
> +	if (ecc->strength >= 8) {
> +		/* 8 bit ECC defaults to BCH ECC on all platforms */
> +		ecc->bytes = wide_bus ? 14 : 13;
> +	} else {
> +		/*
> +		 * if the controller supports BCH for 4 bit ECC, the controller
> +		 * uses lesser bytes for ECC. If RS is used, the ECC bytes is
> +		 * always 10 bytes
> +		 */
> +		if (this->ecc_modes & ECC_BCH_4BIT)
> +			ecc->bytes = wide_bus ? 8 : 7;
> +		else
> +			ecc->bytes = 10;
> +	}
> +
> +	/* each step consists of 512 bytes of data */
> +	ecc->size = NANDC_STEP_SIZE;
> +
> +	ecc->read_page		= qcom_nandc_read_page;
> +	ecc->read_oob		= qcom_nandc_read_oob;
> +	ecc->write_page		= qcom_nandc_write_page;
> +	ecc->write_oob		= qcom_nandc_write_oob;
> +
> +	/*
> +	 * the bad block marker is readable only when we read the page with ECC
> +	 * disabled. all the ops above run with ECC enabled. We need raw read
> +	 * and write function for oob in order to access bad block marker.
> +	 */
> +	ecc->read_oob_raw	= qcom_nandc_read_oob_raw;
> +	ecc->write_oob_raw	= qcom_nandc_write_oob_raw;
> +
> +	switch (mtd->oobsize) {
> +	case 64:
> +		ecc->layout = &layout_oob_64;
> +		break;
> +	case 128:
> +		ecc->layout = &layout_oob_128;
> +		break;
> +	case 224:
> +		if (wide_bus)
> +			ecc->layout = &layout_oob_224_x16;
> +		else
> +			ecc->layout = &layout_oob_224_x8;
> +		break;
> +	case 256:
> +		ecc->layout = &layout_oob_256;
> +		break;
> +	default:
> +		dev_err(this->dev, "unsupported NAND device, oobsize %d\n",
> +			mtd->oobsize);
> +		return -ENODEV;
> +	}
> +
> +	ecc->mode = NAND_ECC_HW;
> +
> +	/* enable ecc by default */
> +	this->use_ecc = true;
> +
> +	return 0;
> +}
> +
> +static void qcom_nandc_hw_post_init(struct qcom_nandc_data *this)
> +{
> +	struct mtd_info *mtd = &this->mtd;
> +	struct nand_chip *chip = &this->chip;
> +	struct nand_ecc_ctrl *ecc = &chip->ecc;
> +	int cwperpage = mtd->writesize / ecc->size;
> +	int spare_bytes, bad_block_byte;
> +	bool wide_bus;
> +	int ecc_mode = 0;
> +
> +	wide_bus = chip->options & NAND_BUSWIDTH_16 ? true : false;
> +
> +	if (ecc->strength >= 8) {
> +		this->cw_size = 532;
> +
> +		spare_bytes = wide_bus ? 0 : 2;
> +
> +		this->bch_enabled = true;
> +		ecc_mode = 1;
> +	} else {
> +		this->cw_size = 528;
> +
> +		if (this->ecc_modes & ECC_BCH_4BIT) {
> +			spare_bytes = wide_bus ? 2 : 4;
> +
> +			this->bch_enabled = true;
> +			ecc_mode = 0;
> +		} else {
> +			spare_bytes = wide_bus ? 0 : 1;
> +		}
> +	}
> +
> +	/*
> +	 * DATA_UD_BYTES varies based on whether the read/write command protects
> +	 * spare data with ECC too. We protect spare data by default, so we set
> +	 * it to main + spare data, which are 512 and 4 bytes respectively.
> +	 */
> +	this->cw_data = 516;
> +
> +	bad_block_byte = mtd->writesize - this->cw_size * (cwperpage - 1) + 1;
> +
> +	this->cfg0 = (cwperpage - 1) << CW_PER_PAGE
> +				| this->cw_data << UD_SIZE_BYTES
> +				| 0 << DISABLE_STATUS_AFTER_WRITE
> +				| 5 << NUM_ADDR_CYCLES
> +				| ecc->bytes << ECC_PARITY_SIZE_BYTES_RS
> +				| 0 << STATUS_BFR_READ
> +				| 1 << SET_RD_MODE_AFTER_STATUS
> +				| spare_bytes << SPARE_SIZE_BYTES;
> +
> +	this->cfg1 = 7 << NAND_RECOVERY_CYCLES
> +				| 0 <<  CS_ACTIVE_BSY
> +				| bad_block_byte << BAD_BLOCK_BYTE_NUM
> +				| 0 << BAD_BLOCK_IN_SPARE_AREA
> +				| 2 << WR_RD_BSY_GAP
> +				| wide_bus << WIDE_FLASH
> +				| this->bch_enabled << ENABLE_BCH_ECC;
> +
> +	this->cfg0_raw = (cwperpage - 1) << CW_PER_PAGE
> +				| this->cw_size << UD_SIZE_BYTES
> +				| 5 << NUM_ADDR_CYCLES
> +				| 0 << SPARE_SIZE_BYTES;
> +
> +	this->cfg1_raw = 7 << NAND_RECOVERY_CYCLES
> +				| 0 << CS_ACTIVE_BSY
> +				| 17 << BAD_BLOCK_BYTE_NUM
> +				| 1 << BAD_BLOCK_IN_SPARE_AREA
> +				| 2 << WR_RD_BSY_GAP
> +				| wide_bus << WIDE_FLASH
> +				| 1 << DEV0_CFG1_ECC_DISABLE;
> +
> +	this->ecc_bch_cfg = this->bch_enabled << ECC_CFG_ECC_DISABLE
> +				| 0 << ECC_SW_RESET
> +				| this->cw_data << ECC_NUM_DATA_BYTES
> +				| 1 << ECC_FORCE_CLK_OPEN
> +				| ecc_mode << ECC_MODE
> +				| ecc->bytes << ECC_PARITY_SIZE_BYTES_BCH;
> +
> +	this->ecc_buf_cfg = 0x203 << NUM_STEPS;
> +
> +	this->clrflashstatus = FS_READY_BSY_N;
> +	this->clrreadstatus = 0xc0;
> +
> +	dev_dbg(this->dev,
> +		"cfg0 %x cfg1 %x ecc_buf_cfg %x ecc_bch cfg %x cw_size %d cw_data %d strength %d parity_bytes %d steps %d\n",
> +		this->cfg0, this->cfg1, this->ecc_buf_cfg,
> +		this->ecc_bch_cfg, this->cw_size, this->cw_data,
> +		ecc->strength, ecc->bytes, cwperpage);
> +}
> +
> +static int qcom_nandc_alloc(struct qcom_nandc_data *this)
> +{
> +	int r;
> +
> +	r = dma_set_coherent_mask(this->dev, DMA_BIT_MASK(32));
> +	if (r) {
> +		dev_err(this->dev, "failed to set DMA mask\n");
> +		return r;
> +	}
> +
> +	/*
> +	 * we use the internal buffer for reading ONFI params, reading small
> +	 * data like ID and status, and preforming read-copy-write operations
> +	 * when writing to a codeword partially. 532 is the maximum possible
> +	 * size of a codeword for our nand controller
> +	 */
> +	this->buf_size = 532;
> +
> +	this->data_buffer = devm_kzalloc(this->dev, this->buf_size, GFP_KERNEL);
> +	if (!this->data_buffer)
> +		return -ENOMEM;
> +
> +	this->regs = devm_kzalloc(this->dev, sizeof(*this->regs), GFP_KERNEL);
> +	if (!this->regs)
> +		return -ENOMEM;
> +
> +	this->reg_read_buf = devm_kzalloc(this->dev,
> +				MAX_REG_RD * sizeof(*this->reg_read_buf),
> +				GFP_KERNEL);
> +	if (!this->reg_read_buf)
> +		return -ENOMEM;
> +
> +	INIT_LIST_HEAD(&this->list);
> +
> +	this->chan = dma_request_slave_channel(this->dev, "rxtx");
> +	if (!this->chan) {
> +		dev_err(this->dev, "failed to request slave channel\n");
> +		return -ENODEV;
> +	}
> +
> +	return 0;
> +}
> +
> +static void qcom_nandc_unalloc(struct qcom_nandc_data *this)
> +{
> +	dma_release_channel(this->chan);
> +}
> +
> +static int qcom_nandc_init(struct qcom_nandc_data *this)
> +{
> +	struct mtd_info *mtd = &this->mtd;
> +	struct nand_chip *chip = &this->chip;
> +	struct device_node *np = this->dev->of_node;
> +	struct mtd_part_parser_data ppdata = { .of_node = np };
> +	int r;
> +
> +	mtd->priv = chip;
> +	mtd->name = "qcom-nandc";
> +	mtd->owner = THIS_MODULE;
> +
> +	chip->priv = this;
> +
> +	chip->cmdfunc		= qcom_nandc_command;
> +	chip->select_chip	= qcom_nandc_select_chip;
> +	chip->read_byte		= qcom_nandc_read_byte;
> +	chip->read_buf		= qcom_nandc_read_buf;
> +	chip->write_buf		= qcom_nandc_write_buf;
> +
> +	chip->options |= NAND_NO_SUBPAGE_WRITE | NAND_USE_BOUNCE_BUFFER;
> +	if (this->bus_width == 16)
> +		chip->options |= NAND_BUSWIDTH_16;
> +
> +	chip->bbt_options = NAND_BBT_ACCESS_BBM_RAW;
> +	if (of_get_nand_on_flash_bbt(np))

Can you use nand_dt_init()? i.e., fill out chip->flash_node and let
nand_scan_ident() take care of most of the common DT parsing. You can
then clean up afterward with something like:

	if (chip->bbt_options & NAND_BBT_USE_FLASH)
		chip->bbt_options |= NAND_BBT_NO_OOB;

Similar for the bus width, ECC strength, and ECC step size parameters.

> +		chip->bbt_options = NAND_BBT_USE_FLASH | NAND_BBT_NO_OOB;
> +
> +	qcom_nandc_pre_init(this);
> +
> +	r = nand_scan_ident(mtd, 1, NULL);
> +	if (r)
> +		return r;
> +
> +	r = qcom_nandc_ecc_init(this);
> +	if (r)
> +		return r;
> +
> +	qcom_nandc_hw_post_init(this);
> +
> +	r = nand_scan_tail(mtd);
> +	if (r)
> +		return r;
> +
> +	return mtd_device_parse_register(mtd, NULL, &ppdata, NULL, 0);
> +}
> +
> +static int qcom_nandc_parse_dt(struct platform_device *pdev)
> +{
> +	struct qcom_nandc_data *this = platform_get_drvdata(pdev);
> +	struct device_node *np = this->dev->of_node;
> +	int r;
> +
> +	this->ecc_strength = of_get_nand_ecc_strength(np);
> +	if (this->ecc_strength < 0) {
> +		dev_warn(this->dev,
> +			"incorrect ecc strength, setting to 4 bits/step\n");
> +		this->ecc_strength = 4;
> +	}
> +
> +	this->bus_width = of_get_nand_bus_width(np);
> +	if (this->bus_width < 0) {
> +		dev_warn(this->dev, "incorrect bus width, setting to 8\n");
> +		this->bus_width = 8;
> +	}
> +
> +	r = of_property_read_u32(np, "qcom,cmd-crci", &this->cmd_crci);
> +	if (r) {
> +		dev_err(this->dev, "command CRCI unspecified\n");
> +		return r;
> +	}
> +
> +	r = of_property_read_u32(np, "qcom,data-crci", &this->data_crci);
> +	if (r) {
> +		dev_err(this->dev, "data CRCI unspecified\n");
> +		return r;
> +	}
> +
> +	return 0;
> +}
> +
> +static int qcom_nandc_probe(struct platform_device *pdev)
> +{
> +	struct qcom_nandc_data *this;
> +	const void *dev_data;
> +	int r;
> +
> +	this = devm_kzalloc(&pdev->dev, sizeof(*this), GFP_KERNEL);
> +	if (!this)
> +		return -ENOMEM;
> +
> +	platform_set_drvdata(pdev, this);
> +
> +	this->pdev = pdev;
> +	this->dev  = &pdev->dev;
> +
> +	dev_data = of_device_get_match_data(&pdev->dev);
> +	if (!dev_data) {
> +		dev_err(&pdev->dev, "failed to get device data\n");
> +		return -ENODEV;
> +	}
> +
> +	this->ecc_modes = (unsigned long)dev_data;
> +
> +	this->res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	this->base = devm_ioremap_resource(&pdev->dev, this->res);
> +	if (IS_ERR(this->base))
> +		return PTR_ERR(this->base);
> +
> +	this->core_clk = devm_clk_get(&pdev->dev, "core");
> +	if (IS_ERR(this->core_clk))
> +		return PTR_ERR(this->core_clk);
> +
> +	this->aon_clk = devm_clk_get(&pdev->dev, "aon");
> +	if (IS_ERR(this->aon_clk))
> +		return PTR_ERR(this->aon_clk);
> +
> +	r = qcom_nandc_parse_dt(pdev);
> +	if (r)
> +		return r;
> +
> +	r = qcom_nandc_alloc(this);
> +	if (r)
> +		return r;
> +
> +	r = clk_prepare_enable(this->core_clk);
> +	if (r)
> +		goto err_core_clk;
> +
> +	r = clk_prepare_enable(this->aon_clk);
> +	if (r)
> +		goto err_aon_clk;
> +
> +	r = qcom_nandc_init(this);
> +	if (r)
> +		goto err_init;
> +
> +	return 0;
> +
> +err_init:
> +	clk_disable_unprepare(this->aon_clk);
> +err_aon_clk:
> +	clk_disable_unprepare(this->core_clk);
> +err_core_clk:
> +	qcom_nandc_unalloc(this);
> +
> +	return r;
> +}
> +
> +static int qcom_nandc_remove(struct platform_device *pdev)
> +{
> +	struct qcom_nandc_data *this = platform_get_drvdata(pdev);
> +
> +	qcom_nandc_unalloc(this);
> +
> +	clk_disable_unprepare(this->aon_clk);
> +	clk_disable_unprepare(this->core_clk);
> +
> +	return 0;
> +}
> +
> +#define EBI2_NANDC_ECC_MODES	(ECC_RS_4BIT | ECC_BCH_8BIT)
> +
> +/*
> + * data will hold a struct pointer containing more differences once we support
> + * more IPs
> + */
> +static const struct of_device_id qcom_nandc_of_match[] = {
> +	{	.compatible = "qcom,ebi2-nandc",
> +		.data = (void *) EBI2_NANDC_ECC_MODES,
> +	},
> +	{}
> +};
> +MODULE_DEVICE_TABLE(of, qcom_nandc_of_match);
> +
> +static struct platform_driver qcom_nandc_driver = {
> +	.driver = {
> +		.name = "qcom-nandc",
> +		.of_match_table = qcom_nandc_of_match,
> +	},
> +	.probe   = qcom_nandc_probe,
> +	.remove  = qcom_nandc_remove,
> +};
> +module_platform_driver(qcom_nandc_driver);
> +
> +MODULE_AUTHOR("Archit Taneja <architt@xxxxxxxxxxxxxx>");
> +MODULE_DESCRIPTION("Qualcomm NAND Controller driver");
> +MODULE_LICENSE("GPL v2");

Brian
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