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.
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?
Yes correct. That at least sounds like the most likely explanation to me.
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...
It won't delay the other CRTCs because each CRTC has it's own kernel
thread, but it won't be optimal either.
Going to try to reproduce the bug with 3.16,
Christian.
_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
http://lists.freedesktop.org/mailman/listinfo/dri-devel
