Re: [V3, 2/2] mtd: brcmnand: Detect sticky ucorr ecc error on dma reads

[Brian Norris <computersforpeace@gmail.com>]

Hi,

Looking through Boris's pull request, I noticed an issue:

On Thu, Jun 09, 2016 at 05:17:55PM -0400, Kamal Dasu wrote:
> This change provides a fix for controller bug where nand
> controller could have a possible sticky error after a PIO
> followed by a DMA read. The fix retries a read if we see
> a uncorr_ecc after read to detect such sticky errors.
> The fix applies to only controller version 7.0 and 7.1.
> 
> Signed-off-by: Kamal Dasu <kdasu.kdev@gmail.com>
> ---
> V3 changes 
>  none
> V2 Changes 
>  Restrict controller bug workaround to version 7.0 and 7.1
> ---
>  drivers/mtd/nand/brcmnand/brcmnand.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/mtd/nand/brcmnand/brcmnand.c b/drivers/mtd/nand/brcmnand/brcmnand.c
> index 7ee9617..1156495 100644
> --- a/drivers/mtd/nand/brcmnand/brcmnand.c
> +++ b/drivers/mtd/nand/brcmnand/brcmnand.c
> @@ -1602,9 +1602,11 @@ static int brcmnand_read(struct mtd_info *mtd, struct nand_chip *chip,
>  	struct brcmnand_controller *ctrl = host->ctrl;
>  	u64 err_addr = 0;
>  	int err;
> +	static bool retry = true;

Is this intentionally static? That means your retry will only be
performed exactly once *ever*. Probably not what you expected?

Boris, if this is indeed unintended, would you rather fix this up in the
original patch and send me a new pull request? Or have my apply the
trivial fixup (i.e., s/static//) as a separate patch on top?

Brian

>  
>  	dev_dbg(ctrl->dev, "read %llx -> %p\n", (unsigned long long)addr, buf);
>  
> +try_dmaread:
>  	brcmnand_write_reg(ctrl, BRCMNAND_UNCORR_COUNT, 0);
>  
>  	if (has_flash_dma(ctrl) && !oob && flash_dma_buf_ok(buf)) {
> @@ -1626,6 +1628,22 @@ static int brcmnand_read(struct mtd_info *mtd, struct nand_chip *chip,
>  
>  	if (mtd_is_eccerr(err)) {
>  		/*
> +		 * On controller version and 7.0, 7.1 , DMA read after a
> +		 * prior PIO read that reported uncorrectable error,
> +		 * the DMA engine captures this error following DMA read
> +		 * cleared only on subsequent DMA read, so just retry once
> +		 * to clear a possible false error reported for current DMA
> +		 * read
> +		 */
> +		if ((ctrl->nand_version == 0x0700) ||
> +		    (ctrl->nand_version == 0x0701)) {
> +			if (retry) {
> +				retry = false;
> +				goto try_dmaread;
> +			}
> +		}
> +
> +		/*
>  		 * Controller version 7.2 has hw encoder to detect erased page
>  		 * bitflips, apply sw verification for older controllers only
>  		 */
> -- 
> 1.9.1
>