Re: [PATCH v5 4/4] drm/fence: add out-fences support

From	Ville Syrjälä <ville.syrjala@linux.intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v5 4/4] drm/fence: add out-fences support
Date	2016-10-20 18:40 +0200
Message-ID	<suoxP-1Cz-11@gated-at.bofh.it> (permalink)
References	<sumZ3-wo-3@gated-at.bofh.it> <sumZ3-wo-21@gated-at.bofh.it> <sunBL-ZF-1@gated-at.bofh.it> <sunV7-161-29@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Thu, Oct 20, 2016 at 01:55:38PM -0200, Gustavo Padovan wrote:
> 2016-10-20 Ville Syrjälä <ville.syrjala@linux.intel.com>:
> 
> > On Thu, Oct 20, 2016 at 12:50:05PM -0200, Gustavo Padovan wrote:
> > > From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > > 
> > > Support DRM out-fences by creating a sync_file with a fence for each CRTC
> > > that sets the OUT_FENCE_PTR property.
> > 
> > I still maintain the out fence should also be per fb (well, per plane
> > since we can't add it to fbs). Otherwise it's not going to be at all
> > useful if you do fps>vrefresh and don't include the same set of planes
> > in every atomic ioctl, eg. if you only ever include ones that are
> > somehow dirty.
> 
> How would the kernel signal these dirty planes then? Right now we signal
> at the vblank.

So if I think about it in terms of the previous fbs something like this
comes to mind:

 starting point:
 plane a, fb 0
 plane b, fb 1

 ioctl:
 plane a, fb 2, fence A
 plane b, fb 3, fence B

 ioctl:
 plane a, fb 4, fence C
 -> fb 2 can be reused, so fence C should signal immediately?

 vblank:
 -> fb 0,1 can be reused, so fence A,B signal?

It feels a bit wonky since the fence is effectively associated with the
previous fb after the previous fb was already submitted to the kernel.
One might assume fence A to be the one signalled early, but that would
give the impression that fb 0 would be free for reuse when it's not.

-- 
Ville Syrjälä
Intel OTC

Thread

[PATCH v5 0/4] drm: add explicit fencing Gustavo Padovan <gustavo@padovan.org> - 2016-10-20 17:00 +0200
  [PATCH v5 4/4] drm/fence: add out-fences support Gustavo Padovan <gustavo@padovan.org> - 2016-10-20 17:00 +0200
    Re: [PATCH v5 4/4] drm/fence: add out-fences support Ville Syrjälä <ville.syrjala@linux.intel.com> - 2016-10-20 17:40 +0200
      Re: [PATCH v5 4/4] drm/fence: add out-fences support Gustavo Padovan <gustavo.padovan@collabora.com> - 2016-10-20 18:00 +0200
        Re: [PATCH v5 4/4] drm/fence: add out-fences support Ville Syrjälä <ville.syrjala@linux.intel.com> - 2016-10-20 18:40 +0200
          Re: [PATCH v5 4/4] drm/fence: add out-fences support Ville Syrjälä <ville.syrjala@linux.intel.com> - 2016-10-20 21:20 +0200
            Re: [PATCH v5 4/4] drm/fence: add out-fences support Daniel Vetter <daniel@ffwll.ch> - 2016-10-21 15:00 +0200
              Re: [PATCH v5 4/4] drm/fence: add out-fences support Gustavo Padovan <gustavo@padovan.org> - 2016-10-21 15:10 +0200
    Re: [PATCH v5 4/4] drm/fence: add out-fences support Brian Starkey <brian.starkey@arm.com> - 2016-10-20 19:50 +0200
      Re: [PATCH v5 4/4] drm/fence: add out-fences support Gustavo Padovan <gustavo@padovan.org> - 2016-10-20 22:40 +0200
        Re: [PATCH v5 4/4] drm/fence: add out-fences support Brian Starkey <brian.starkey@arm.com> - 2016-10-21 13:00 +0200
          Re: [PATCH v5 4/4] drm/fence: add out-fences support Daniel Vetter <daniel@ffwll.ch> - 2016-10-21 15:10 +0200
    Re: [PATCH v5 4/4] drm/fence: add out-fences support Brian Starkey <brian.starkey@arm.com> - 2016-10-21 17:50 +0200
  Re: [PATCH v5 0/4] drm: add explicit fencing Daniel Vetter <daniel@ffwll.ch> - 2016-10-21 15:10 +0200

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