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

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Date:	Fri, 22 Jan 2016 17:18:35 +0200
From:	Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:	Michel Dänzer <michel@...nzer.net>
Cc:	Mario Kleiner <mario.kleiner.de@...il.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	LKML <linux-kernel@...r.kernel.org>,
	dri-devel@...ts.freedesktop.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 Fri, Jan 22, 2016 at 12:06:00PM +0900, Michel Dänzer wrote:
> 
> [ Trimming KDE folks from Cc ]
> 
> On 21.01.2016 19:09, Daniel Vetter wrote:
> > On Thu, Jan 21, 2016 at 05:36:46PM +0900, Michel Dänzer wrote:
> >> On 21.01.2016 16:58, Daniel Vetter wrote:
> >>> 
> >>> Can you please point me at the vblank on/off jump bug please?
> >>
> >> AFAIR I originally reported it in response to
> >> http://lists.freedesktop.org/archives/dri-devel/2015-August/087841.html
> >> , but I can't find that in the archives, so maybe that was just on IRC.
> >> See
> >> http://lists.freedesktop.org/archives/dri-devel/2016-January/099122.html
> >> . Basically, I ran into the bug fixed by your patch because the counter
> >> jumped forward on every DPMS off, so it hit the 32-bit boundary after
> >> just a few days.
> > 
> > Ok, so just uncovered the overflow bug.
> 
> Not sure what you mean by "just", but to be clear: The drm_vblank_on/off
> counter jumping bug (similar to the bug this thread is about), which
> exposed the overflow bug, is still alive and kicking in 4.5. It seems
> to happen when turning off the CRTC:
> 
> [drm:drm_update_vblank_count] updating vblank count on crtc 0: current=218104694, diff=0, hw=916 hw_last=916
> [drm:radeon_get_vblank_counter_kms] crtc 0: dist from vblank start 3
> [drm:drm_calc_vbltimestamp_from_scanoutpos] crtc 0 : v 0x7 p(2199,-45)@ 7304.307354 -> 7304.308006 [e 0 us, 0 rep]
> [drm:radeon_get_vblank_counter_kms] crtc 0: dist from vblank start 3
> [drm:drm_update_vblank_count] updating vblank count on crtc 0: current=218104694, diff=16776301, hw=1 hw_last=916

Not sure what bug we're talking about here, but here the hw counter
clearly jumps backwards.

> [drm:radeon_get_vblank_counter_kms] Query failed! stat 3
> [drm:radeon_get_vblank_counter_kms] Query failed! stat 3
> [drm:drm_update_vblank_count] updating vblank count on crtc 1: current=0, diff=0, hw=0 hw_last=0
> [drm:radeon_get_vblank_counter_kms] Query failed! stat 3
> [drm:radeon_get_vblank_counter_kms] Query failed! stat 3
> [drm:drm_update_vblank_count] updating vblank count on crtc 2: current=0, diff=0, hw=0 hw_last=0
> [drm:radeon_get_vblank_counter_kms] Query failed! stat 3
> [drm:radeon_get_vblank_counter_kms] Query failed! stat 3
> [drm:drm_update_vblank_count] updating vblank count on crtc 3: current=0, diff=0, hw=0 hw_last=0
> [drm:radeon_get_vblank_counter_kms] Query failed! stat 1
> [drm:drm_calc_vbltimestamp_from_scanoutpos] crtc 0 : v 0x1 p(0,0)@ 7304.317140 -> 7304.317140 [e 0 us, 0 rep]
> [drm:radeon_get_vblank_counter_kms] Query failed! stat 1
> [drm:drm_update_vblank_count] updating vblank count on crtc 0: current=234880995, diff=16777215, hw=0 hw_last=1

Same here.

These things just don't happen on i915 because drm_vblank_off() and
drm_vblank_on() are always called around the times when the hw counter
might get reset. Or at least that's how it should be.

> dev->max_vblank_count = 0xffffffff, which makes the wraparound code in
> drm_update_vblank_count a no-op. Maybe you can reproduce it if you
> artificially set a lower max_vblank_count in the driver.
> 
> 
> -- 
> Earthling Michel Dänzer               |               http://www.amd.com
> Libre software enthusiast             |             Mesa and X developer

-- 
Ville Syrjälä
Intel OTC