[PATCH 1/2] Revert "drm/radeon: remove drm_vblank_get|put from pflip handling"

[Dieter Nützel]

Am 23.06.2014 11:34, schrieb Michel Dänzer:
> On 18.06.2014 18:14, Christian König wrote:
>> Am 18.06.2014 07:53, schrieb Michel Dänzer:
>>> 
>>> Looking into these issues has got me thinking about the use of the 
>>> page
>>> flip interrupt: If the page flip interrupt arrives before the
>>> corresponding
>>> vertical blank interrupt, the DRM vblank counter will be lower than
>>> expected by 1 in drm_send_vblank_event(). I suspect this is the cause 
>>> of
>>> 
>>>   (WW) RADEON(0): radeon_dri2_flip_event_handler: Pageflip completion
>>> event has impossible msc [x-1] < target_msc [x]
>>> 
>>> messages in the X log file which have been popping up in bug reports
>>> lately.
>>> This also results in 0s being returned to the client for the MSC and
>>> timestamp of the swap completion, which could cause all kinds of bad
>>> behaviour.
>> First of all thanks for looking into it. Are you getting this on 3.16 
>> or
>> 3.15?
> 
> I haven't actually run into this myself yet. I thought I'd seen it in
> several bug reports, but right now I can only find
> https://bugs.freedesktop.org/show_bug.cgi?id=80029#c17 , which seems to
> include the page flipping changes from 3.16.

With 3.16-rc2 I get it now on my RV730 AGP as in the above bug report.
But only the lines in Xorg.0.log.
NO signs of any damage/error in use.

Since 3.15 and 3.16 (rc2 only) my system is rock solid.

I've tried 3.15-rc7 + Christian's pflip rework (did some little 
handwork), too.
It was solid but I saw the reported flip/black distortion in the below 
part during Kwin 4.13 cube screen effect (rotation). Your fix for 
3.16-rc1 fixed that.

Before 3.15/3.16-rcX I got some hangs from time to time during system 
boot.
Nothing in the logs but SSD RAID1 rebuild. Maybe it was MD related an 
NOT r600/DRM.

3.16-rcX (3.15-rc7+pflip patches) seems to be more responsive that 3.15, 
for me.

First and latest attchments from bug #80141
https://bugs.freedesktop.org/attachment.cgi?id=101605
show same.

Where should I add/send my Xorg.0.log?

Cheers,
   Dieter

>> I don't think that the pflip irq is thrown earlier than the vblank, 
>> but
>> on 3.16 it might actually be that we program the flip so fast into the
>> hardware that we do it one frame earlier than planned.
> 
> So userspace is notified of the previous vertical blank period and 
> calls
> the page flip ioctl in response, which then manages to program the
> scanout address update into the hardware before the scanout address
> update is latched during the previous vertical blank period?
> 
> To avoid that scenario, one possibility might be to check if we're in
> vertical blank before calling radeon_page_flip(), and if so sleep for
> 1ms or so before trying again? That might unnecessarily delay flips on
> other CRTCs though...