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

[Rodrigo Vivi]

Ok, so after trying it we saw that we really cannot trust on aux mutex.At
least not on all SKL/KBL
It worked in a KBL but failed on a SKL that I have here...

So without aux mutex option we still need to get sink_crc more reliable and
I see only 2 quick ways here:
- This read wake
- Return -EBUSY to force the drm retries on message size = 0.

Daniel, what do you believe?

Please let me know witch way and if necessary I rebase the patch and
re-send.

Thanks,
Rodrigo.




On Wed, Oct 21, 2015 at 8:27 PM Thulasimani, Sivakumar <
sivakumar.thulasimani at intel.com> wrote:

>
>
> 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.
>
> regards,
> Sivakumar
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