On Fri, May 09, 2014, Sonny Rao wrote:
> On Thu, May 8, 2014 at 2:42 AM, Yuvaraj Kumar <yuvaraj.cd@xxxxxxxxx> 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@xxxxxxxxx> wrote:
> >> From: Doug Anderson <dianders@xxxxxxxxxxxx>
> >>
> >> 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@xxxxxxxxxxxx>
> >> Signed-off-by: Yuvaraj Kumar C D <yuvaraj.cd@xxxxxxxxx>
> >> ---
> >> 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
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