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

[Daniel Vetter]

On Mon, Nov 16, 2015 at 04:05:42PM +0000, Rodrigo Vivi wrote:
> 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?

It's still a mess. My opinion is still that we should move the hacks from
read_wake into a more suitable place:
a) either into drm_dp_dpcd_read in drm_dp_helper.c
b) or into intel_dp_aux_transfer in intel_dp.c

Option a) is the right one if this is a generic sink issue (and it seems
to be the case, at least for edp panels). Option b) if it's an issue with
our hw. Either way I think intel_dp_dpcd_read_wake should die.

On a personal gut level I'd go with option a).

Cheers, Daniel

> 
> 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
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> >

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch