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

[Seungwon Jeon <tgih.jun@samsung.com>]

On Fri, May 09, 2014, Sonny Rao wrote:
> On Thu, May 8, 2014 at 2:42 AM, Yuvaraj Kumar <yuvaraj.cd@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@gmail.com> wrote:
> >> From: Doug Anderson <dianders@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.
I think repeating is not good approach to fix race.
In your case, XFER_COMPLETE preceded data error and DTO didn't come?
It seems strange case.
I want to know actual error value if you can reproduce.

> >> 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@chromium.org>
> >> Signed-off-by: Yuvaraj Kumar C D <yuvaraj.cd@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;
> >> +                               }
Can you explain what happens above?
What is it for?

Thanks,
Seungwon Jeon