Question about implicit fence sync in display DRM drivers

[Qiang Yu]

OK, meson has fix from Koen and Neil. I'll send the fix for sun4i.
But rockchip and exynos need the help from Simon and Heiko because I
don't have a device.

Regards,
Qiang
On Wed, Nov 21, 2018 at 5:45 PM Daniel Vetter <daniel at ffwll.ch> wrote:
>
> On Sun, Nov 18, 2018 at 08:44:57PM +0800, Qiang Yu wrote:
> >  add ".prepare_fb = drm_gem_fb_prepare_fb," in "drm_plane_helper_funcs"
> > solve my flicker problem on Allwinner A64.
>
> Yeah, some drivers fail to set this. Would be great if you could submit
> this bugfix.
>
> Thanks, Daniel
>
> >
> > Thanks,
> > Qiang
> > On Sun, Nov 18, 2018 at 8:14 PM Qiang Yu <yuq825 at gmail.com> wrote:
> > >
> > > I find the reservation object will be created when: dma_buf_export
> > > if no reservation object created when buffer object creation.
> > >
> > > And the implicit fence can be synced before display in: drm_gem_fb_prepare_fb
> > > but seems most display driver doesn't call this function.
> > >
> > > Regards,
> > > Qiang
> > > On Sun, Nov 18, 2018 at 10:43 AM Qiang Yu <yuq825 at gmail.com> wrote:
> > > >
> > > > Hi Eric and Wladimir,
> > > >
> > > > GPU driver like VC4, Etnaviv and Lima only do rendering and left display
> > > > to other DRM display drivers. So there should be a render/display sync
> > > > problem for these drivers.
> > > >
> > > > As I know, there are two ways: implicit and explicit described here:
> > > > https://www.collabora.com/news-and-blog/blog/2016/09/13/mainline-explicit-fencing-part-1/
> > > >
> > > > The implicit way need the display DRM driver wait on the reservation object
> > > > associated with that framebuffer before display it, the reservation
> > > > object contains
> > > > fence which is added by render DRM driver to indicate render finish:
> > > > https://www.phoronix.com/scan.php?page=news_item&px=AMDGPU-Intel-4.9-PRIME-Ex-Patch
> > > >
> > > > I investigate a bit into these DRM display drivers using CMA GEM helpers,
> > > > seems there's no reservation object at all, so it should be impossible to
> > > > support implicit sync.
> > > >
> > > > Although explicit way is better, there are still some apps not support it like
> > > > kodi-gbm. So how do VC4+PL111 and Etnaviv+IMX solve this sync problem,
> > > > and do these drivers support implicit sync?
> > > >
> > > > Thanks,
> > > > Qiang
> > _______________________________________________
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> > dri-devel at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch