Re: [PATCH v2 4/6] mtd: nand: gpmi: correct bitflip for erased NAND page

[Boris Brezillon <boris.brezillon@free-electrons.com>]

On Fri, 10 Jun 2016 12:01:32 -0500
Han Xu <han.xu@nxp.com> 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.
> 
> Signed-off-by: Han Xu <han.xu@nxp.com>
> ---
>  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 | 27 ++++++++++++++++++++++++++-
>  3 files changed, 41 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/nand/gpmi-nand/bch-regs.h b/drivers/mtd/nand/gpmi-nand/bch-regs.h
> index 228142c..2c44b88 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 358ff5d..0b5666a 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);
> +
>  	/* 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 aedaff3..03bdb4d 100644
> --- a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
> +++ b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
> @@ -1043,6 +1043,7 @@ static int gpmi_ecc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
>  {
>  	struct gpmi_nand_data *this = nand_get_controller_data(chip);
>  	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;
> @@ -1051,6 +1052,8 @@ 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 bitflips = 0;
> +	int bitflip_flag = 0;

Hm, I would choose another name, but I'm not even sure this is really
needed (see below).

>  
>  	dev_dbg(this->dev, "page number is : %d\n", page);
>  	ret = read_page_prepare(this, buf, nfc_geo->payload_size,
> @@ -1088,8 +1091,20 @@ static int gpmi_ecc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
>  			   payload_virt, payload_phys);
>  
>  	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)) {
> +				bitflips = readl(bch_regs + HW_BCH_DEBUG1);

You could use ret here or define a flips variable locally to this code
(see what's done for the software correction).

BTW, why not memset-ing the data chunk here (as done for the SW
correction part). This way you wouldn't need the extra bitflips_flag
variable.

> +				if (bitflips) {
> +					bitflip_flag = 1;
> +					max_bitflips = max_t(unsigned int,
> +							     max_bitflips,
> +							     bitflips);
> +				}
> +			}
>  			continue;
> +		}
>  
>  		if (*status == STATUS_UNCORRECTABLE) {
>  			int eccbits = nfc_geo->ecc_strength * nfc_geo->gf_len;
> @@ -1098,6 +1113,10 @@ static int gpmi_ecc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
>  			int eccbytes;
>  			int flips;
>  
> +			/* shortcut for i.MX7 and i.MX6QP */
> +			if (GPMI_IS_MX6QP(this) || GPMI_IS_MX7(this))

You should increment mtd->ecc_stats.failed in this case.

> +				continue;
> +
>  			/* Read ECC bytes into our internal raw_buffer */
>  			offset = nfc_geo->metadata_size * 8;
>  			offset += ((8 * nfc_geo->ecc_chunk_size) + eccbits) * (i + 1);
> @@ -1182,6 +1201,12 @@ static int gpmi_ecc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
>  		chip->oob_poi[0] = ((uint8_t *) auxiliary_virt)[0];
>  	}
>  
> +	/* if bitflip occurred in erased page, change data to all 0xff */
> +	if (bitflip_flag) {
> +		memset(buf, ~0, nfc_geo->payload_size);
> +		memset(chip->oob_poi, ~0, mtd->oobsize);
> +	}
> +
>  	return max_bitflips;
>  }
>  



-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com