[Mesa-dev] [PATCH 8/8] panfrost: Add backend targeting the DRM driver

[Dave Airlie]

On Tue, 5 Mar 2019 at 12:20, Kristian Høgsberg <hoegsberg at gmail.com> wrote:
>
> On Mon, Mar 4, 2019 at 6:11 PM Alyssa Rosenzweig <alyssa at rosenzweig.io> wrote:
> >
> > > Why aren't we using regular dma-buf fences here? The submit ioctl
> > > should be able to take a number of in fences to wait on and return an
> > > out fence if requested.
> >
> > Ah-ha, that sounds like the "proper" approach for mainline. Much of this
> > was (incorrectly) inherited from the Arm driver. Thank you for the
> > pointer.
>
> I'm not sure - I mean, the submit should take in/out fences, but the
> atom mechanism here sounds more like it's for declaring the
> dependencies between multiple batches in a renderpass/frame to allow
> the kernel to shcedule them? The sync fd may be a little to heavy
> handed for that, and if you want to express that kind of dependency to
> allow the kernel to reschedule, maybe we need both?

You should more likely be using syncobjects, not fences.

You can convert syncobjs to fences, but fences consume an fd which you
only really want if inter-device.

Dave.