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@chris-wilson.co.uk Cc: Ville Syrjälä ville.syrjala@linux.intel.com Cc: stable@vger.kernel.org # v4.4+ Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103326 Signed-off-by: Imre Deak imre.deak@intel.com
Acked-by: Chris Wilson chris@chris-wilson.co.uk -Chris