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

[Sonny Rao]

On Thu, May 8, 2014 at 2:42 AM, Yuvaraj Kumar <yuvaraj.cd at gmail.com> wrote:
> Any comments on this patch?
>

I'll just add that without this fix, running the tuning loop for UHS
modes is not reliable on dw_mmc because errors will happen and you
will eventually hit this race and hang.  This can happen any time
there is tuning like during boot or during resume from suspend.

> 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
>>