Quoting Imre Deak (2018-01-30 11:47:10)
> Currently we see sporadic timeouts during CDCLK changing both on BXT and
> GLK as reported by the Bugzilla: ticket. It's easy to reproduce this by
> changing the frequency in a tight loop after blanking the display. The
> upper bound for the completion time is 800us based on my tests, so
> increase it from the current 500us to 2ms; with that I couldn't trigger
> the problem either on BXT or GLK.
>
> Note that timeouts happened during both the change notification and the
> voltage level setting PCODE request. (For the latter one BSpec doesn't
> require us to wait for completion before further HW programming.)
>
> This issue is similar to
> 2c7d0602c815 ("drm/i915/gen9: Fix PCODE polling during CDCLK change
> notification")
> but there the PCODE request does complete (as shown by the mbox
> busy flag), only the reply we get from PCODE indicates a failure.
> So there we keep resending the request until a success reply, here we
> just have to increase the timeout for the one PCODE request we send.
>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v4.4+
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103326
> Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx>
Acked-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
-Chris