[PATCH] RFC: mmc: dw_mmc: Always go to STATE_DATA_BUSY from STATE_DATA_ERROR

Doug Anderson
2013-03-15T21:29:47Z

On a flaky piece of hardware that seems good at generating CRC errors,
we have found that often times the CRC errors don't get reported
properly when using CONFIG_MMC_DW_IDMAC (they get reported OK when
using pio).

The flow that happens is:
1. dw_mci_interrupt() fires and status=80b8, pending=8088 so that
we hit (pending & DW_MCI_DATA_ERROR_FLAGS). We store 8088 in
data_status and set EVENT_DATA_ERROR in host->pending_events
2. We schedule the tasklet and it runs.
3. We're in STATE_SENDING_DATA in the tasklet and see
EVENT_DATA_ERROR so we dw_mci_stop_dma().
4. dw_mci_stop_dma() calls dw_mci_idmac_stop_dma() and
dw_mci_dma_cleanup(). These stop dma but _don't_ set
EVENT_XFER_COMPLETE (since we're host->using_dma).
5. data->stop is NULL so we don't send a stop command.
6. We move onto STATE_DATA_ERROR and loop again in the tasklet.
7. We hit STATE_DATA_ERROR but the transfer isn't done, so the tasklet
stops.

We never seem to get any additional DMA interrupts that cause
EVENT_XFER_COMPLETE and restart the tasklet so we just hang. That
doesn't seem surprising given that we've stopped DMA.

We did put a print at the end of dw_mci_interrupt() to show the result
of the "mci_readl(host, IDSTS)" and saw 0xa000 in the case of the
above CRC error.

A proposed fix for this is to ignore (but still clear) the
EVENT_XFER_COMPLETE in STATE_DATA_ERROR in the tasklet.

Reported-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: Doug Anderson <dianders@chromium.org>
---
drivers/mmc/host/dw_mmc.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
index 9834221..696b3bb 100644
--- a/drivers/mmc/host/dw_mmc.c
+++ b/drivers/mmc/host/dw_mmc.c
@@ -1137,10 +1137,7 @@ static void dw_mci_tasklet_func(unsigned long priv)
goto unlock;

case STATE_DATA_ERROR:
- if (!test_and_clear_bit(EVENT_XFER_COMPLETE,
- &host->pending_events))
- break;
-
+ clear_bit(EVENT_XFER_COMPLETE, &host->pending_events);
state = STATE_DATA_BUSY;
break;
}
--
1.8.1.3