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

["Michel Dänzer" <michel@daenzer.net>]

On 21.01.2016 15:38, Michel Dänzer wrote:
> On 21.01.2016 14:31, Mario Kleiner wrote:
>> On 01/21/2016 04:43 AM, Michel Dänzer wrote:
>>> 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?
>>>
>>
>> The whole logic has changed and the software counter updates are now
>> driven all the time by the hw counter.
>>
>>>
>>> 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...
>>
>> I spent the last few hours reading through the drm and radeon code and i
>> think what should probably work is to replace the
>> drm_vblank_pre/post_modeset calls in radeon/amdgpu by drm_vblank_off/on
>> calls. These are apparently meant for drivers whose hw counters reset
>> during modeset, [...]
> 
> ... just like drm_vblank_pre/post_modeset. That those were broken is a
> regression which needs to be fixed anyway. I don't think switching to
> drm_vblank_on/off is suitable for stable trees.

Even more so since as I mentioned, there is (has been since at least
about half a year ago) a counter jumping bug with drm_vblank_on/off as well.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer