Re: [PATCH v5 3/5] mtd: Add support for HyperBus memory devices

[Sergei Shtylyov]

On 06/09/2019 01:32 PM, Vignesh Raghavendra wrote:

> Cypress' HyperBus is Low Signal Count, High Performance Double Data Rate
> Bus interface between a host system master and one or more slave
> interfaces. HyperBus is used to connect microprocessor, microcontroller,
> or ASIC devices with random access NOR flash memory (called HyperFlash)
> or self refresh DRAM (called HyperRAM).
> 
> Its a 8-bit data bus (DQ[7:0]) with  Read-Write Data Strobe (RWDS)
> signal and either Single-ended clock(3.0V parts) or Differential clock
> (1.8V parts). It uses ChipSelect lines to select b/w multiple slaves.
> At bus level, it follows a separate protocol described in HyperBus
> specification[1].
> 
> HyperFlash follows CFI AMD/Fujitsu Extended Command Set (0x0002) similar
> to that of existing parallel NORs. Since HyperBus is x8 DDR bus,
> its equivalent to x16 parallel NOR flash wrt bits per clock cycle. But
> HyperBus operates at >166MHz frequencies.
> HyperRAM provides direct random read/write access to flash memory
> array.
> 
> But, HyperBus memory controllers seem to abstract implementation details
> and expose a simple MMIO interface to access connected flash.
> 
> Add support for registering HyperFlash devices with MTD framework. MTD
> maps framework along with CFI chip support framework are used to support
> communicating with flash.
> 
> Framework is modelled along the lines of spi-nor framework. HyperBus
> memory controller (HBMC) drivers calls hyperbus_register_device() to
> register a single HyperFlash device. HyperFlash core parses MMIO access
> information from DT, sets up the map_info struct, probes CFI flash and
> registers it with MTD framework.
> 
> Some HBMC masters need calibration/training sequence[3] to be carried
> out, in order for DLL inside the controller to lock, by reading a known
> string/pattern. This is done by repeatedly reading CFI Query
> Identification String. Calibration needs to be done before trying to detect
> flash as part of CFI flash probe.
> 
> HyperRAM is not supported at the moment.
> 
> HyperBus specification can be found at[1]
> HyperFlash datasheet can be found at[2]
> 
> [1] https://www.cypress.com/file/213356/download
> [2] https://www.cypress.com/file/213346/download
> [3] http://www.ti.com/lit/ug/spruid7b/spruid7b.pdf
>     Table 12-5741. HyperFlash Access Sequence
> 
> Signed-off-by: Vignesh Raghavendra <vigneshr@xxxxxx>
[...]
> diff --git a/drivers/mtd/hyperbus/hyperbus-core.c b/drivers/mtd/hyperbus/hyperbus-core.c
> new file mode 100644
> index 000000000000..df1f75e10b1a
> --- /dev/null
> +++ b/drivers/mtd/hyperbus/hyperbus-core.c
> @@ -0,0 +1,191 @@
> +// SPDX-License-Identifier: GPL-2.0
> +//
> +// Copyright (C) 2019 Texas Instruments Incorporated - http://www.ti.com/
> +// Author: Vignesh Raghavendra <vigneshr@xxxxxx>
> +
> +#include <linux/err.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/mtd/hyperbus.h>
> +#include <linux/mtd/map.h>
> +#include <linux/mtd/mtd.h>
> +#include <linux/mtd/cfi.h>
> +#include <linux/of.h>
> +#include <linux/of_address.h>
> +#include <linux/types.h>
> +
> +#define HYPERBUS_CALIB_COUNT 25

   Mhm, I think I've already protested about this being #define'd here...

[...]
> +int hyperbus_register_device(struct hyperbus_device *hbdev)
> +{
> +	const struct hyperbus_ops *ops;
> +	struct hyperbus_ctlr *ctlr;
> +	struct device_node *np;
> +	struct map_info *map;
> +	struct resource res;
> +	struct device *dev;
> +	int ret;
> +
> +	if (!hbdev || !hbdev->np || !hbdev->ctlr || !hbdev->ctlr->dev) {
> +		pr_err("hyperbus: please fill all the necessary fields!\n");
> +		return -EINVAL;
> +	}
> +
> +	np = hbdev->np;
> +	ctlr = hbdev->ctlr;
> +	if (!of_device_is_compatible(np, "cypress,hyperflash"))
> +		return -ENODEV;
> +
> +	hbdev->memtype = HYPERFLASH;
> +
> +	if (of_address_to_resource(np, 0, &res))
> +		return -EINVAL;

   Why not just propagate the error upstream (yeah, I've noticed that
it only can be -EINVAL)?

[...]
> diff --git a/include/linux/mtd/hyperbus.h b/include/linux/mtd/hyperbus.h
> new file mode 100644
> index 000000000000..ee2eefd822c9
> --- /dev/null
> +++ b/include/linux/mtd/hyperbus.h
> @@ -0,0 +1,91 @@
> +/* SPDX-License-Identifier: GPL-2.0
> + *
> + * Copyright (C) 2019 Texas Instruments Incorporated - http://www.ti.com/
> + */
> +
> +#ifndef __LINUX_MTD_HYPERBUS_H__
> +#define __LINUX_MTD_HYPERBUS_H__
> +
> +#include <linux/mtd/map.h>
> +
> +enum hyperbus_memtype {
> +	HYPERFLASH,
> +	HYPERRAM,
> +};
> +
> +/**
> + * struct hyperbus_device - struct representing HyperBus slave device
> + * @map: map_info struct for accessing MMIO HyperBus flash memory
> + * @np:	pointer to HyperBus slave device node
          ^
   Space needed here, not tab.

> + * @mtd: pointer to MTD struct
> + * @ctlr: pointer to HyperBus controller struct
> + * @memtype: type of memory device: HyperFlash or HyperRAM
> + * @registered: flag to indicate whether device is registered with MTD core
> + */
> +
> +struct hyperbus_device {
> +	struct map_info map;
> +	struct device_node *np;
> +	struct mtd_info *mtd;
> +	struct hyperbus_ctlr *ctlr;
> +	enum hyperbus_memtype memtype;
> +	bool registered;
> +};
> +
> +/**
> + * struct hyperbus_ops - struct representing custom HyperBus operations
> + * @read16: read 16 bit of data, usually from register/ID-CFI space
> + * @write16: write 16 bit of data, usually to register/ID-CFI space

   Usually? How to differ the register/memory transfers if both are possible?

> + * @copy_from: copy data from flash memory
> + * @copy_to: copy data to flash memory
> + * @calibrate: calibrate HyperBus controller
> + */
> +
> +struct hyperbus_ops {
> +	u16 (*read16)(struct hyperbus_device *hbdev, unsigned long addr);
> +	void (*write16)(struct hyperbus_device *hbdev,
> +			unsigned long addr, u16 val);
> +	void (*copy_from)(struct hyperbus_device *hbdev, void *to,
> +			  unsigned long from, ssize_t len);
> +	void (*copy_to)(struct hyperbus_device *dev, unsigned long to,
> +			const void *from, ssize_t len);
> +	int (*calibrate)(struct hyperbus_device *dev);
> +};
> +
> +/**
> + * struct hyperbus_ctlr - struct representing HyperBus controller
> + * @calibrated: flag to indicate ctlr calibration sequence is complete
> + * @ops: HyperBus controller ops

   What about @dev?

> + */
> +struct hyperbus_ctlr {
> +	struct device *dev;
> +	bool calibrated;
> +
> +	const struct hyperbus_ops *ops;
> +};
[...]

MBR, Sergei