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

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

On Fri, 29 Apr 2016 16:21:25 -0400
Kamal Dasu <kdasu.kdev@gmail.com> 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.
> 
> Signed-off-by: Kamal Dasu <kdasu.kdev@gmail.com>
> ---
>  drivers/mtd/nand/brcmnand/brcmnand.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/nand/brcmnand/brcmnand.c b/drivers/mtd/nand/brcmnand/brcmnand.c
> index 29a9abd..13c7784 100644
> --- a/drivers/mtd/nand/brcmnand/brcmnand.c
> +++ b/drivers/mtd/nand/brcmnand/brcmnand.c
> @@ -1555,9 +1555,11 @@ static int brcmnand_read(struct mtd_info *mtd, struct nand_chip *chip,
>  	struct brcmnand_controller *ctrl = host->ctrl;
>  	u64 err_addr = 0;
>  	int err;
> +	bool retry = true;
>  
>  	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)) {
> @@ -1579,7 +1581,18 @@ static int brcmnand_read(struct mtd_info *mtd, struct nand_chip *chip,
>  
>  	if (mtd_is_eccerr(err)) {
>  		int ret;
> -
> +		/*
> +		 * On controller version >=7.0 if we are doing a 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
> +		 */

Hm, shouldn't this BRCMNAND_UNCORR_COUNT bit be cleared just after
doing the PIO/DMA read instead of doing it before executing a new read?
This would solve your problem without the need for this extra retry, or
am I missing something?

> +		if ((ctrl->nand_version >= 0x0700) && retry) {
> +			retry = false;
> +			goto try_dmaread;
> +		}
>  		ret = brcmstb_nand_verify_erased_page(mtd, chip, buf, addr);
>  		if (ret < 0) {
>  			dev_dbg(ctrl->dev, "uncorrectable error at 0x%llx\n",



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