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

[Mario Kleiner]

On 01/22/2016 04:18 PM, Ville Syrjälä wrote:
> 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.
>

Fwiw, testing the HD-57570 single display with my patch that uses 
drm_vblank_off/on() in the DPMS OFF/ON path of radeon-kms does show 
hardware counter reset to zero as expected, but no jumps of software 
vblank counter. So with that vblank_off/on placement it seems to work 
nicely here.

-mario

>> 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
>