RE: [PATCH v2] mmc: dw_mmc: Make sure we don't get stuck when we get an error

Seungwon Jeon
2014-05-21T09:08:30Z

On Wed, May 21, 2014, Doug Anderson wrote:
> 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@chromium.org>
> Signed-off-by: Yuvaraj Kumar C D <yuvaraj.cd@gmail.com>

It will be applied after "mmc: dw_mmc: change to use recommended reset procedure"

Acked-by: Seungwon Jeon <tgih.jun@samsung.com>

Thanks,
Seungwon Jeon

> ---
> Changes in v2:
> - Removed TODO
> - Set cmd to NULL before calling dw_mci_request_end()
>
> drivers/mmc/host/dw_mmc.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 46 insertions(+)
>
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index cced599..54ec8b0 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -1318,6 +1318,14 @@ 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);
> @@ -1331,7 +1339,29 @@ 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:
> @@ -1354,6 +1384,22 @@ 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.
> + */
> + if (!test_bit(EVENT_CMD_COMPLETE,
> + &host->pending_events)) {
> + host->cmd = NULL;
> + dw_mci_request_end(host, mrq);
> + goto unlock;
> + }
> }
>
> /*
> --
> 1.9.1.423.g4596e3a