[RFC] NAND: Optimize NAND_ECC_HW_OOB_FIRST read

[Boris Brezillon]

Hi PrasannaKumar,

On Sat, 28 Oct 2017 13:13:51 +0530
PrasannaKumar Muralidharan <prasannatsmkumar at gmail.com> wrote:

> From: Lars-Peter Clausen <lars at metafoo.de>
> 
> Avoid sending unnecessary READ commands to the chip.
> 
> Signed-off-by: Lars-Peter Clausen <lars at metafoo.de>
> Signed-off-by: PrasannaKumar Muralidharan <prasannatsmkumar at gmail.com>
> ---
> This patch is taken from git://projects.qi-hardware.com/qi-kernel.git
> branch jz-3.16. From [1] and [2] it can be seen that the patch author
> thinks this can be sent upstream but it never happened so far. This
> patch is used in OpenWRT as seen from [3].

Sounds reasonable, but it's likely to conflict with something I'd like
to queue for 4.16 [1]. I'll rebase this patch on nand/next once the
->exec_op() series is merged. Don't hesitate to ping me if I forget.

Regards,

Boris

[1]http://patchwork.ozlabs.org/project/linux-mtd/list/?series=8923

> 
> I have only compile tested the patch.
> 
> 1. https://www.mail-archive.com/discussion@lists.en.qi-hardware.com/msg04635.html
> 2. https://www.mail-archive.com/discussion@lists.en.qi-hardware.com/msg04639.html
> 3. https://git.lede-project.org/?p=source.git;a=blob;f=target/linux/xburst/patches-3.18/002-NAND-Optimize-NAND_ECC_HW_OOB_FIRST-read.patch;h=046da51912de3cd4444779df5de13d2c1999719a;hb=c03d4317a6bc891cb4a5e89cbdd77f37c23aff86
> 
>  drivers/mtd/nand/nand_base.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> index 12edaae..4bf3bdb 100644
> --- a/drivers/mtd/nand/nand_base.c
> +++ b/drivers/mtd/nand/nand_base.c
> @@ -1680,9 +1680,15 @@ static int nand_read_page_hwecc_oob_first(struct mtd_info *mtd,
>  	unsigned int max_bitflips = 0;
>  
>  	/* Read the OOB area first */
> -	chip->cmdfunc(mtd, NAND_CMD_READOOB, 0, page);
> -	chip->read_buf(mtd, chip->oob_poi, mtd->oobsize);
> -	chip->cmdfunc(mtd, NAND_CMD_READ0, 0, page);
> +	if (mtd->writesize > 512) {
> +		chip->cmdfunc(mtd, NAND_CMD_READ0, mtd->writesize, page);
> +		chip->read_buf(mtd, chip->oob_poi, mtd->oobsize);
> +		chip->cmdfunc(mtd, NAND_CMD_RNDOUT, 0, -1);
> +	} else {
> +		chip->cmdfunc(mtd, NAND_CMD_READOOB, 0, page);
> +		chip->read_buf(mtd, chip->oob_poi, mtd->oobsize);
> +		chip->cmdfunc(mtd, NAND_CMD_READ0, 0, page);
> +	}
>  
>  	ret = mtd_ooblayout_get_eccbytes(mtd, ecc_code, chip->oob_poi, 0,
>  					 chip->ecc.total);
> @@ -1902,8 +1908,10 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
>  						 __func__, buf);
>  
>  read_retry:
> -			if (nand_standard_page_accessors(&chip->ecc))
> +			if (nand_standard_page_accessors(&chip->ecc) &&
> +			    chip->ecc.mode != NAND_ECC_HW_OOB_FIRST) {
>  				chip->cmdfunc(mtd, NAND_CMD_READ0, 0x00, page);
> +			}
>  
>  			/*
>  			 * Now read the page into the buffer.  Absent an error,