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

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Message-ID: <56A053CE.7000500@daenzer.net>
Date:	Thu, 21 Jan 2016 12:43:10 +0900
From:	Michel Dänzer <michel@...nzer.net>
To:	Mario Kleiner <mario.kleiner.de@...il.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:	Daniel Vetter <daniel.vetter@...ll.ch>,
	LKML <linux-kernel@...r.kernel.org>,
	dri-devel@...ts.freedesktop.org, mgraesslin@....org, kwin@....org,
	Alex Deucher <alexander.deucher@....com>,
	Christian König <christian.koenig@....com>
Subject: Re: linux-4.4 bisected: kwin5 stuck on kde5 loading screen with
 radeon

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               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer