Re: [RESEND PATCH v2 1/1] mmc: dw_mmc: Wait for data transfer after response errors.

[Enric Balletbo Serra]

Hi Jaehoon,

2016-06-20 12:14 GMT+02:00 Jaehoon Chung <jh80.chung@xxxxxxxxxxx>:
> Hi Enric,
>
> On 04/26/2016 05:03 PM, Enric Balletbo i Serra wrote:
>> From: Doug Anderson <dianders@xxxxxxxxxxxx>
>>
>> According to the DesignWare state machine description, after we get a
>> "response error" or "response CRC error" we move into data transfer
>> mode. That means that we don't necessarily need to special case
>> trying to deal with the failure right away. We can wait until we are
>> notified that the data transfer is complete (with or without errors)
>> and then we can deal with the failure.
>>
>> It may sound strange to defer dealing with a command that we know will
>> fail anyway, but this appears to fix a bug. During tuning (CMD19) on
>> a specific card on an rk3288-based system, we found that we could get
>> a "response CRC error". Sending the stop command after the "response
>> CRC error" would then throw the system into a confused state causing
>> all future tuning phases to report failure.
>
> I understood this patch what purpose has.
> Does it need to consider for other tuning cases?
>

Not sure, to be honest I only saw this during UHS tuning sequence on
this brand of cards I never reproduced the issue on other tuning
cases.

> Best Regards,
> Jaehoon Chung
>
>>
>> When in the confused state, the controller would show these (hex codes
>> are interrupt status register):
>>  CMD ERR: 0x00000046 (cmd=19)
>>  CMD ERR: 0x0000004e (cmd=12)
>>  DATA ERR: 0x00000208
>>  DATA ERR: 0x0000020c
>>  CMD ERR: 0x00000104 (cmd=19)
>>  CMD ERR: 0x00000104 (cmd=12)
>>  DATA ERR: 0x00000208
>>  DATA ERR: 0x0000020c
>>  ...
>>  ...
>>
>> It is inherently difficult to deal with the complexity of trying to
>> correctly send a stop command while a data transfer is taking place
>> since you need to deal with different corner cases caused by the fact
>> that the data transfer could complete (with errors or without errors)
>> during various places in sending the stop command (dw_mci_stop_dma,
>> send_stop_abort, etc)
>>
>> Instead of adding a bunch of extra complexity to deal with this, it
>> seems much simpler to just use the more straightforward (and less
>> error-prone) path of letting the data transfer finish. There
>> shouldn't be any huge benefit to sending the stop command slightly
>> earlier, anyway.
>>
>> Signed-off-by: Doug Anderson <dianders@xxxxxxxxxxxx>
>> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@xxxxxxxxxxxxx>
>> Cc: Alim Akhtar <alim.akhtar@xxxxxxxxx>
>> ---
>> Changelog since v1:
>> - Fix the issue found by Alim with exynos letting the data transfer
>>   take place only when MMC_SEND_TUNING_BLOCK is issued.
>>
>>  drivers/mmc/host/dw_mmc.c | 27 +++++++++++++++++++++++++++
>>  1 file changed, 27 insertions(+)
>>
>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
>> index 242f9a0..2ebeea8 100644
>> --- a/drivers/mmc/host/dw_mmc.c
>> +++ b/drivers/mmc/host/dw_mmc.c
>> @@ -1761,6 +1761,33 @@ static void dw_mci_tasklet_func(unsigned long priv)
>>                       }
>>
>>                       if (cmd->data && err) {
>> +                             /*
>> +                              * During UHS tuning sequence, sending the stop
>> +                              * command after the response CRC error would
>> +                              * throw the system into a confused state
>> +                              * causing all future tuning phases to report
>> +                              * failure.
>> +                              *
>> +                              * In such case controller will move into a data
>> +                              * transfer state after a response error or
>> +                              * response CRC error. Let's let that finish
>> +                              * before trying to send a stop, so we'll go to
>> +                              * STATE_SENDING_DATA.
>> +                              *
>> +                              * Although letting the data transfer take place
>> +                              * will waste a bit of time (we already know
>> +                              * the command was bad), it can't cause any
>> +                              * errors since it's possible it would have
>> +                              * taken place anyway if this tasklet got
>> +                              * delayed. Allowing the transfer to take place
>> +                              * avoids races and keeps things simple.
>> +                              */
>> +                             if ((err != -ETIMEDOUT) &&
>> +                                 (cmd->opcode == MMC_SEND_TUNING_BLOCK)) {
>> +                                     state = STATE_SENDING_DATA;
>> +                                     continue;
>> +                             }
>> +
>>                               dw_mci_stop_dma(host);
>>                               send_stop_abort(host, data);
>>                               state = STATE_SENDING_STOP;
>>
>
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