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

[Vlastimil Babka]

On 01/21/2016 09:28 AM, Mario Kleiner wrote:
>> ... 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.
>>
>> Looking at Vlastimil's original post again, I'd say the most likely
>> culprit is 4dfd6486 ("drm: Use vblank timestamps to guesstimate how many
>> vblanks were missed").
>>

Yeah, this is what I bisected to.

> Yes, i think reverting that one alone would likely fix it by reverting
> to the old vblank update logic.

Yep I said in the original mail that reverting on top of 4.4 fixed it. 
Well not just this single commit, but also some patches on top (e.g. 
radeon and amdgpu adaptations to that commit, IIRC it wouldn't have 
compiled otherwise).

>>
>>> Once drm_vblank_off is called, drm_vblank_get will no-op and return an
>>> error, so clients can't enable vblank irqs during the modeset - pageflip
>>> ioctl and waitvblank ioctl would fail while a modeset happens -
>>> hopefully userspace handles this correctly everywhere.
>>
>> We've fixed xf86-video-ati for this.
>>
>>
>>> I'll hack up a patch for demonstration now.
>>
>> You're a bit late to that party. :)
>>
>> http://lists.freedesktop.org/archives/dri-devel/2015-May/083614.html
>> http://lists.freedesktop.org/archives/dri-devel/2015-July/086451.html
>>
>>
>
> Oops. Just sent out my little (so far untested) creations. Yes, they are
> essentially the same as Daniel's patches. The only addition is to also
> fix that other potential small race i describe by slightly moving the
> xxx_pm_compute_clocks() calls around. And a fix for drm_vblank_get/put
> imbalance in radeon_pm if vblank_on/off would be used.

Thanks, I'll test.

>
> -mario
>