[PATCH] mmc: dw_mmc: Make sure we don't get stuck when we get an error

[Yuvaraj Kumar]

Any comments on this patch?

On Thu, Mar 27, 2014 at 11:48 AM, Yuvaraj Kumar C D
<yuvaraj.cd at gmail.com> wrote:
> From: Doug Anderson <dianders at chromium.org>
>
> If we happened to get a data error at just the wrong time the dw_mmc
> driver could get into a state where it would never complete its
> request.  That would leave the caller just hanging there.
>
> We fix this two ways and both of the two fixes on their own appear to
> fix the problems we've seen:
>
> 1. Fix a race in the tasklet where the interrupt setting the data
>    error happens _just after_ we check for it, then we get a
>    EVENT_XFER_COMPLETE.  We fix this by repeating a bit of code.
> 2. Fix it so that if we detect that we've got an error in the "data
>    busy" state and we're not going to do anything else we end the
>    request and unblock anyone waiting.
>
> Signed-off-by: Doug Anderson <dianders at chromium.org>
> Signed-off-by: Yuvaraj Kumar C D <yuvaraj.cd at gmail.com>
> ---
>  drivers/mmc/host/dw_mmc.c |   47 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 47 insertions(+)
>
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index 1d77431..4c589f1 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -1300,6 +1300,14 @@ static void dw_mci_tasklet_func(unsigned long priv)
>                         /* fall through */
>
>                 case STATE_SENDING_DATA:
> +                       /*
> +                        * We could get a data error and never a transfer
> +                        * complete so we'd better check for it here.
> +                        *
> +                        * Note that we don't really care if we also got a
> +                        * transfer complete; stopping the DMA and sending an
> +                        * abort won't hurt.
> +                        */
>                         if (test_and_clear_bit(EVENT_DATA_ERROR,
>                                                &host->pending_events)) {
>                                 dw_mci_stop_dma(host);
> @@ -1313,7 +1321,29 @@ static void dw_mci_tasklet_func(unsigned long priv)
>                                 break;
>
>                         set_bit(EVENT_XFER_COMPLETE, &host->completed_events);
> +
> +                       /*
> +                        * Handle an EVENT_DATA_ERROR that might have shown up
> +                        * before the transfer completed.  This might not have
> +                        * been caught by the check above because the interrupt
> +                        * could have gone off between the previous check and
> +                        * the check for transfer complete.
> +                        *
> +                        * Technically this ought not be needed assuming we
> +                        * get a DATA_COMPLETE eventually (we'll notice the
> +                        * error and end the request), but it shouldn't hurt.
> +                        *
> +                        * This has the advantage of sending the stop command.
> +                        */
> +                       if (test_and_clear_bit(EVENT_DATA_ERROR,
> +                                              &host->pending_events)) {
> +                               dw_mci_stop_dma(host);
> +                               send_stop_abort(host, data);
> +                               state = STATE_DATA_ERROR;
> +                               break;
> +                       }
>                         prev_state = state = STATE_DATA_BUSY;
> +
>                         /* fall through */
>
>                 case STATE_DATA_BUSY:
> @@ -1336,6 +1366,23 @@ static void dw_mci_tasklet_func(unsigned long priv)
>                                 /* stop command for open-ended transfer*/
>                                 if (data->stop)
>                                         send_stop_abort(host, data);
> +                       } else {
> +                               /*
> +                                * If we don't have a command complete now we'll
> +                                * never get one since we just reset everything;
> +                                * better end the request.
> +                                *
> +                                * If we do have a command complete we'll fall
> +                                * through to the SENDING_STOP command and
> +                                * everything will be peachy keen.
> +                                *
> +                                * TODO: I guess we shouldn't send a stop?
> +                                */
> +                               if (!test_bit(EVENT_CMD_COMPLETE,
> +                                             &host->pending_events)) {
> +                                       dw_mci_request_end(host, mrq);
> +                                       goto unlock;
> +                               }
>                         }
>
>                         /*
> --
> 1.7.10.4
>