linux-4.4 bisected: kwin5 stuck on kde5 loading screen with radeon

Michel Dänzer michel at
Wed Jan 20 19:43:10 PST 2016

On 21.01.2016 05:32, Mario Kleiner wrote:
> So the problem is that AMDs hardware frame counters reset to
> zero during a modeset. The old DRM code dealt with drivers doing that by
> keeping vblank irqs enabled during modesets and incrementing vblank
> count by one during each vblank irq, i think that's what
> drm_vblank_pre_modeset() and drm_vblank_post_modeset() were meant for.

Right, looks like there's been a regression breaking this. I suspect the
problem is that vblank->last isn't getting updated from
drm_vblank_post_modeset. Not sure which change broke that though, or how
to fix it. Ville?

BTW, I'm seeing a similar issue with drm_vblank_on/off as well, which
exposed the bug fixed by 209e4dbc ("drm/vblank: Use u32 consistently for
vblank counters"). I've been meaning to track that down since then; one
of these days hopefully, but if anybody has any ideas offhand...

Earthling Michel Dänzer               |     
Libre software enthusiast             |             Mesa and X developer

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