[Intel-gfx] [PATCH 03/11] drm/i915: Add a delay in Displayport AUX transactions for compliance testing

[Todd Previte]

Fixed the commit message. That will be in V5 of the patch set to be 
posted today.

On 4/7/2015 6:57 AM, Paulo Zanoni wrote:
> 2015-04-06 23:09 GMT-03:00 Todd Previte <tprevite at gmail.com>:
>> The Displayport Link Layer Compliance Testing Specification 1.2 rev 1.1
>> specifies that repeated AUX transactions after a failure (no response /
>> invalid response) must have a minimum delay of 400us before the resend can
>> occur. Tests 4.2.1.1 and 4.2.1.2 are two tests that require this specifically.
>>
>> Also, the check for DP_AUX_CH_CTL_TIME_OUT_ERROR has been moved out into a
>> separate case. As of now, the only action taken is to log the error, since
>> the HW will have already waited the required amount of time for the
>> transaction to complete.
> As of V6, this paragraph is no longer true. We could just remove it
> while applying.
>
> With that: Reviewed-by: Paulo Zanoni <paulo.r.zanoni at intel.com>.
>
>> V2:
>> - Changed udelay() to usleep_range()
>> V3:
>> - Removed extraneous check for timeout
>> - Updated comment to reflect this change
>> V4:
>> - Reformatted a comment
>> V5:
>> - Added separate check for HW timeout on AUX transactions. A message
>>    is logged upon detection of this case.
>> V6:
>> - Add continue statement to HW timeout detect case
>> - Remove the log message indicating a timeout has been
>>    detected (review feedback)
>>
>> Signed-off-by: Todd Previte <tprevite at gmail.com>
>> ---
>>   drivers/gpu/drm/i915/intel_dp.c | 13 +++++++++++--
>>   1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
>> index ed2f60c..8b59458 100644
>> --- a/drivers/gpu/drm/i915/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/intel_dp.c
>> @@ -877,9 +877,18 @@ intel_dp_aux_ch(struct intel_dp *intel_dp,
>>                                     DP_AUX_CH_CTL_TIME_OUT_ERROR |
>>                                     DP_AUX_CH_CTL_RECEIVE_ERROR);
>>
>> -                       if (status & (DP_AUX_CH_CTL_TIME_OUT_ERROR |
>> -                                     DP_AUX_CH_CTL_RECEIVE_ERROR))
>> +                       if (status & DP_AUX_CH_CTL_TIME_OUT_ERROR)
>>                                  continue;
>> +
>> +                       /* DP CTS 1.2 Core Rev 1.1, 4.2.1.1 & 4.2.1.2
>> +                        *   400us delay required for errors and timeouts
>> +                        *   Timeout errors from the HW already meet this
>> +                        *   requirement so skip to next iteration
>> +                        */
>> +                       if (status & DP_AUX_CH_CTL_RECEIVE_ERROR) {
>> +                               usleep_range(400, 500);
>> +                               continue;
>> +                       }
>>                          if (status & DP_AUX_CH_CTL_DONE)
>>                                  break;
>>                  }
>> --
>> 1.9.1
>>
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>
>