[Intel-gfx] [PATCH] drm/i915: Use dpcd read wake for sink crc calls.

Thulasimani, Sivakumar sivakumar.thulasimani at intel.com
Wed Oct 21 20:26:48 PDT 2015

On 10/22/2015 1:44 AM, Damien Lespiau wrote:
> On Thu, Oct 22, 2015 at 12:01:21AM +0530, Thulasimani, Sivakumar wrote:
>> On 8/25/2015 2:50 AM, Vivi, Rodrigo wrote:
>>> On Mon, 2015-08-24 at 19:54 +0000, Zanoni, Paulo R wrote:
>>>> Em Qui, 2015-08-20 às 16:23 -0700, Rodrigo Vivi escreveu:
>>>>> Let's use a native read with retry as suggested per spec to
>>>>> fix Sink CRC on SKL when PSR is enabled.
>>>>> With PSR enabled panel is probably taking more time to wake
>>>>> and dpcd read is faling.
>>>> Does this commit actually fix any known problem with Sink CRC? Or is
>>>> it
>>>> just a try? It would be nice to have this clarified in the commit
>>>> message.
>>> It was just a try but that made sink crc working on my SKL when PSR is
>>> enabled. nothing much to add...
>> SKL has new register AUX_MUTEX which should be used when accessing dpcd
>> on edp. just searched the nightly code and could not find it. it might be
>> the reason
>> for random dpcd failures reported in the other thread.
> We had patches for that back in December 2013 :)
> The feedback from Art was:
>      The non-software aux users are PSR/SRD and GTC.
>      Better leave out the mutex for now. Hardware is going to try do the
>      arbitration itself. I expect you will then need to increase any software
>      timeout you may have.
> Do you know if anything has changed since then?
Not sure, it is in the bspec sequence to use AUX hence forwarded. Art 
might be the
right person to contact :). it might be due to some minor DPCD access 
issues we
observed in BDW when PSR was enabled.


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