[PATCH v2 4/7] drm/panfrost: Add the ability to create submit queues

[Boris Brezillon]

On Fri, 2 Jul 2021 09:58:06 -0400
Alyssa Rosenzweig <alyssa at collabora.com> wrote:

> > > My Vulkan knowledge is limited so I'm not sure whether this is the right
> > > approach or not. In particular is it correct that an application can
> > > create a high priority queue which could affect other (normal priority)
> > > applications?  
> > 
> > That's what msm does (with no extra CAPS check AFAICT), and the
> > freedreno driver can already create high priority queues if
> > PIPE_CONTEXT_HIGH_PRIORITY is passed. Not saying that's okay to allow
> > userspace to tweak the priority, but if that's a problem, other drivers
> > are in trouble too ;-).  
> 
> Speaking of, how will PIPE_CONTEXT_HIGH_PRIORITY be implemented with the
> new ioctl()? I envisioned something much simpler (for the old ioctl),
> just adding a "high priority?" flag to the submit and internally
> creating the two queues of normal/high priority for drm_sched to work
> out. Is this juggling now moved to userspace?

That's what freedreno does. I guess we could create 2 default queues
(one normal and one high prio) and extend the old submit ioctl() to do
what you suggest if you see a good reason to not switch to the new
ioctl() directly. I mean, we'll have to keep support for both anyway,
but switching to the new ioctl()) shouldn't be that hard (I can prepare
a MR transitioning the gallium driver to BATCH_SUBMIT if you want).