On 07/11/17 07:26 AM, Dhinakaran Pandiyan wrote: > Some HW vblank counters reset due to power management events, which messes > up the vblank counting logic. This leads to screen freezes with user space > waiting on vblank events that may not occur if the counter keeps resetting. > > For e.g., After the HW vblank counter resets > [ 9.007359] [drm:drm_update_vblank_count [drm]] updating vblank count > on crtc 0: current=297, diff=4294965389, hw=5 hw_last=1912 > > So, fall back to the SW counter, computed using vblank timestamps > and frame duration, when the HW counter value deviates by 50% of the SW > computed value. > > I have tested this patch on my SKL laptop with i915.enable_psr=1 and it > *seems* to solve the screen freeze issue seen with PSR when DMC is loaded. > > Known issues: > 1) The 50% deviation margin is arbitrary. > 2) "Redundant vblirq ignored" messages are more frequent. > > I am sending this as an RFC to get feedback on whether the fall back > approach is sane and if it should be implemented in the core. Is there no way for the driver to know under which circumstances the reset to 0 might happen? If there is, maybe it could be solved by calling drm_crtc_vblank_off() before it might happen and drm_crtc_vblank_on() after it might have happened. Otherwise, might it be better not to use the HW counter at all when it's known not to be reliable? -- Earthling Michel Dänzer | http://www.amd.com Libre software enthusiast | Mesa and X developer _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
