Re: [PATCH v8 6/7] mtd: nand: gpmi: correct bitflip for erased NAND page

From: Han Xu
Date: Wed Feb 17 2016 - 17:36:23 EST

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On Tue, Feb 2, 2016 at 7:28 AM, Markus Pargmann <mpa@xxxxxxxxxxxxxx> wrote:
> Hi,
>
> On Saturday, January 23, 2016 03:01:47 PM Brian Norris wrote:
>> + Markus Pargmann
>>
>> On Wed, Dec 02, 2015 at 04:47:45PM -0600, Han Xu wrote:
>> > i.MX6QP and i.MX7D BCH module integrated a new feature to detect the
>> > bitflip number for erased NAND page. So for these two platform, set the
>> > erase threshold to ecc_strength and if bitflip detected, GPMI driver will
>> > correct the data to all 0xFF.
>>
>> Looks like Marcus is also trying to add SW correction for the same
>> issue:
>>
>> http://patchwork.ozlabs.org/patch/559557/
>>
>> How do those 2 interact (if at all)?
>
> Thanks for CCing.
>
>>
>> Brian
>>
>> > Signed-off-by: Han Xu <b45815@xxxxxxxxxxxxx>
>> > ---
>> > drivers/mtd/nand/gpmi-nand/bch-regs.h | 10 ++++++++++
>> > drivers/mtd/nand/gpmi-nand/gpmi-lib.c | 5 +++++
>> > drivers/mtd/nand/gpmi-nand/gpmi-nand.c | 24 +++++++++++++++++++++++-
>> > drivers/mtd/nand/gpmi-nand/gpmi-nand.h | 5 ++++-
>> > 4 files changed, 42 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/drivers/mtd/nand/gpmi-nand/bch-regs.h b/drivers/mtd/nand/gpmi-nand/bch-regs.h
>> > index 53e58bc..a84d72b 100644
>> > --- a/drivers/mtd/nand/gpmi-nand/bch-regs.h
>> > +++ b/drivers/mtd/nand/gpmi-nand/bch-regs.h
>> > @@ -30,7 +30,13 @@
>> > #define BM_BCH_CTRL_COMPLETE_IRQ (1 << 0)
>> >
>> > #define HW_BCH_STATUS0 0x00000010
>> > +
>> > #define HW_BCH_MODE 0x00000020
>> > +#define BP_BCH_MODE_ERASE_THRESHOLD 0
>> > +#define BM_BCH_MODE_ERASE_THRESHOLD (0xff << BP_BCH_MODE_ERASE_THRESHOLD)
>> > +#define BF_BCH_MODE_ERASE_THRESHOLD(v) \
>> > + (((v) << BP_BCH_MODE_ERASE_THRESHOLD) & BM_BCH_MODE_ERASE_THRESHOLD)
>> > +
>> > #define HW_BCH_ENCODEPTR 0x00000030
>> > #define HW_BCH_DATAPTR 0x00000040
>> > #define HW_BCH_METAPTR 0x00000050
>> > @@ -125,4 +131,8 @@
>> > )
>> >
>> > #define HW_BCH_VERSION 0x00000160
>> > +#define HW_BCH_DEBUG1 0x00000170
>> > +#define BP_BCH_DEBUG1_ERASED_ZERO_COUNT 0
>> > +#define BM_BCH_DEBUG1_ERASED_ZERO_COUNT \
>> > + (0x1ff << BP_BCH_DEBUG1_ERASED_ZERO_COUNT)
>> > #endif
>> > diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-lib.c b/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
>> > index 1f26a79..0548d84 100644
>> > --- a/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
>> > +++ b/drivers/mtd/nand/gpmi-nand/gpmi-lib.c
>> > @@ -298,6 +298,11 @@ int bch_set_geometry(struct gpmi_nand_data *this)
>> > | BF_BCH_FLASH0LAYOUT1_DATAN_SIZE(block_size, this),
>> > r->bch_regs + HW_BCH_FLASH0LAYOUT1);
>> >
>> > + /* Set erase threshold to ecc_strength for mx6qp and mx7 */
>> > + if (GPMI_IS_MX6QP(this) || GPMI_IS_MX7(this))
>> > + writel(BF_BCH_MODE_ERASE_THRESHOLD(ecc_strength),
>> > + r->bch_regs + HW_BCH_MODE);
>
> This is probably different on imx6qp and imx7?!
> On the other imx6 processors, setting this will instruct the BCH engine
> to allow 'ecc_strength' number of bitflips in an erased area without a
> reported ECC error. Unfortunately it does not fix the bitflips.
>
> So what happens on imx6q,dl,s in this case:
> 1) BCH detects bitflips in the erased page, but ignores them due to the
> ERASE_THRESHOLD setting up to 'ecc_strength' bitflips.
> 2) The gpmi driver does not notice any errors as BCH did not set that
> there is any ECC error in the data. So the driver assumes correct data
> and does not fix the existing bitflips in the erased page.
> 3) UBI does not see any ECC errors and does not check the page.
> 4) UBIFS does check the content of erased pages at some points and
> breaks at this point. The filesystem can't be mounted anymore.
>
> This is why I added my patch a software check in case of an
> uncorrectable ECC error. The ERASE_THRESHOLD has to be 0 for this to
> work.
>
> As this patch only affects imx6qp and imx7, I assume that there is a
> better mechanism now.

IC team add this new feature in i.mx6qp and i.mx7 for bitflip, which
provide a easy way to fix the issue, while we still need some SW check
for other i.mx6 platforms. So these patches don't conflict with
others.

Han Xu

>
> Best Regards,
>
> Markus
>
>> > +
>> > /* Set *all* chip selects to use layout 0. */
>> > writel(0, r->bch_regs + HW_BCH_LAYOUTSELECT);
>> >
>> > diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
>> > index 9f67f0f..9dea56e 100644
>> > --- a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
>> > +++ b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
>> > @@ -71,6 +71,12 @@ static const struct gpmi_devdata gpmi_devdata_imx6q = {
>> > .max_chain_delay = 12,
>> > };
>> >
>> > +static const struct gpmi_devdata gpmi_devdata_imx6qp = {
>> > + .type = IS_MX6QP,
>> > + .bch_max_ecc_strength = 40,
>> > + .max_chain_delay = 12,
>> > +};
>> > +
>> > static const struct gpmi_devdata gpmi_devdata_imx6sx = {
>> > .type = IS_MX6SX,
>> > .bch_max_ecc_strength = 62,
>> > @@ -1010,6 +1016,7 @@ static int gpmi_ecc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
>> > {
>> > struct gpmi_nand_data *this = chip->priv;
>> > struct bch_geometry *nfc_geo = &this->bch_geometry;
>> > + void __iomem *bch_regs = this->resources.bch_regs;
>> > void *payload_virt;
>> > dma_addr_t payload_phys;
>> > void *auxiliary_virt;
>> > @@ -1018,6 +1025,7 @@ static int gpmi_ecc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
>> > unsigned char *status;
>> > unsigned int max_bitflips = 0;
>> > int ret;
>> > + int flag = 0;
>> >
>> > dev_dbg(this->dev, "page number is : %d\n", page);
>> > ret = read_page_prepare(this, buf, nfc_geo->payload_size,
>> > @@ -1050,9 +1058,16 @@ static int gpmi_ecc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
>> > status = auxiliary_virt + nfc_geo->auxiliary_status_offset;
>> >
>> > for (i = 0; i < nfc_geo->ecc_chunk_count; i++, status++) {
>> > - if ((*status == STATUS_GOOD) || (*status == STATUS_ERASED))
>> > + if (*status == STATUS_GOOD)
>> > continue;
>> >
>> > + if (*status == STATUS_ERASED) {
>> > + if (GPMI_IS_MX6QP(this) || GPMI_IS_MX7(this))
>> > + if (readl(bch_regs + HW_BCH_DEBUG1))
>> > + flag = 1;
>> > + continue;
>> > + }
>> > +
>> > if (*status == STATUS_UNCORRECTABLE) {
>> > mtd->ecc_stats.failed++;
>> > continue;
>> > @@ -1081,6 +1096,10 @@ static int gpmi_ecc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
>> > nfc_geo->payload_size,
>> > payload_virt, payload_phys);
>> >
>> > + /* if bitflip occurred in erased page, change data to all 0xff */
>> > + if (flag)
>> > + memset(buf, 0xff, nfc_geo->payload_size);
>> > +
>> > return max_bitflips;
>> > }
>> >
>> > @@ -1990,6 +2009,9 @@ static const struct of_device_id gpmi_nand_id_table[] = {
>> > .compatible = "fsl,imx6q-gpmi-nand",
>> > .data = &gpmi_devdata_imx6q,
>> > }, {
>> > + .compatible = "fsl,imx6qp-gpmi-nand",
>> > + .data = (void *)&gpmi_devdata_imx6qp,
>> > + }, {
>> > .compatible = "fsl,imx6sx-gpmi-nand",
>> > .data = &gpmi_devdata_imx6sx,
>> > }, {
>> > diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-nand.h b/drivers/mtd/nand/gpmi-nand/gpmi-nand.h
>> > index 58b3d69..149a442 100644
>> > --- a/drivers/mtd/nand/gpmi-nand/gpmi-nand.h
>> > +++ b/drivers/mtd/nand/gpmi-nand/gpmi-nand.h
>> > @@ -123,6 +123,7 @@ enum gpmi_type {
>> > IS_MX23,
>> > IS_MX28,
>> > IS_MX6Q,
>> > + IS_MX6QP,
>> > IS_MX6SX,
>> > IS_MX7D,
>> > };
>> > @@ -306,9 +307,11 @@ void gpmi_copy_bits(u8 *dst, size_t dst_bit_off,
>> > #define GPMI_IS_MX23(x) ((x)->devdata->type == IS_MX23)
>> > #define GPMI_IS_MX28(x) ((x)->devdata->type == IS_MX28)
>> > #define GPMI_IS_MX6Q(x) ((x)->devdata->type == IS_MX6Q)
>> > +#define GPMI_IS_MX6QP(x) ((x)->devdata->type == IS_MX6QP)
>> > #define GPMI_IS_MX6SX(x) ((x)->devdata->type == IS_MX6SX)
>> > #define GPMI_IS_MX7D(x) ((x)->devdata->type == IS_MX7D)
>> >
>> > -#define GPMI_IS_MX6(x) (GPMI_IS_MX6Q(x) || GPMI_IS_MX6SX(x))
>> > +#define GPMI_IS_MX6(x) (GPMI_IS_MX6Q(x) || GPMI_IS_MX6QP(x)\
>> > + || GPMI_IS_MX6SX(x))
>> > #define GPMI_IS_MX7(x) (GPMI_IS_MX7D(x))
>> > #endif
>>
>
> --
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>
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>

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