Re: [PATCHv2] mmc: block: Check for errors after write on SPI

[Ulf Hansson <ulf.hansson@linaro.org>]

On Wed, 23 Mar 2022 at 15:12, Christian Löhle <CLoehle@hyperstone.com> wrote:
>
> Introduce a SEND_STATUS check for writes through SPI to not mark
> an unsuccessful write as successful.
>
> Since SPI SD/MMC does not have states, after a write, the card will
> just hold the line LOW until it is ready again. The driver marks the
> write therefore as completed as soon as it reads something other than
> all zeroes.
> The driver does not distinguish from a card no longer signalling busy
> and it being disconnected (and the line being pulled-up by the host).
> This lead to writes being marked as successful when disconnecting
> a busy card.
> Now the card is ensured to be still connected by an additional CMD13,
> just like non-SPI is ensured to go back to TRAN state.
>
> While at it and since we already poll for the post-write status anyway,
> we might as well check for SPIs error bits (any of them).
>
> The disconnecting card problem is reproducable for me after continuous
> write activity and randomly disconnecting, around every 20-50 tries
> on SPI DS for some card.
>
> Fixes: 7213d175e3b6f ("MMC/SD card driver learns SPI")
> Cc: stable@vger.kernel.org
> Signed-off-by: Christian Loehle <cloehle@hyperstone.com>
> ---
> v2:
>   - Reorder err and status check for err to take precedence and look cleaner
>
>  drivers/mmc/core/block.c | 27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/core/block.c b/drivers/mmc/core/block.c
> index 4e67c1403cc9..54c2009f398f 100644
> --- a/drivers/mmc/core/block.c
> +++ b/drivers/mmc/core/block.c
> @@ -1903,9 +1903,34 @@ static int mmc_blk_card_busy(struct mmc_card *card, struct request *req)
>         struct mmc_blk_busy_data cb_data;
>         int err;
>
> -       if (mmc_host_is_spi(card->host) || rq_data_dir(req) == READ)
> +       if (rq_data_dir(req) == READ)
>                 return 0;
>
> +       /*
> +        * SPI does not have a TRAN state we have to wait on, instead the
> +        * card is ready again when it no longer holds the line LOW.
> +        * We still have to ensure two things here before we know the write
> +        * was successful:
> +        * 1. The card has not disconnected during busy and we actually read our
> +        * own pull-up, thinking it was still connected, so ensure it
> +        * still responds.
> +        * 2. Check for any error bits, in particular R1_SPI_IDLE to catch a
> +        * just reconnected card after being disconnected during busy.
> +        */
> +       if (mmc_host_is_spi(card->host)) {
> +               u32 status = 0;
> +
> +               err = __mmc_send_status(card, &status, 0);
> +               /* All R1 and R2 bits of SPI are errors in our case */
> +               if (err || status) {
> +                       mqrq->brq.data.bytes_xfered = 0;
> +                       if (err)
> +                               return err;
> +                       return -EIO;
> +               }
> +               return 0;
> +       }

Nitpick: Would you mind moving the above spi specific code into a
separate function instead?

> +
>         cb_data.card = card;
>         cb_data.status = 0;
>         err = __mmc_poll_for_busy(card->host, 0, MMC_BLK_TIMEOUT_MS,

Other than the above, this looks good to me.

Kind regards
Uffe