Re: [PATCH v7 1/2] drm/panthor: Make the timeout per-queue instead of per-job

[Boris Brezillon <boris.brezillon@collabora.com>]

On Thu, 13 Nov 2025 11:56:03 +0100
Philipp Stanner <pstanner@redhat.com> wrote:

> On Wed, 2025-11-12 at 15:12 +0100, Boris Brezillon wrote:
> > On Wed, 12 Nov 2025 14:48:51 +0100
> > Philipp Stanner <pstanner@redhat.com> wrote:
> >   
> > >   
> 
> […]
> 
> > > >     
> > > > > 
> > > > > You could write a proper drm_sched API function which serves your
> > > > > usecase.    
> > > > 
> > > > It's not really lack of support for our usecase that drives this
> > > > change, but more the fact the current helpers are racy for drivers that
> > > > have a 1:1 entity:sched relationship with queues that can be scheduled
> > > > out behind drm_gpu_scheduler's back.    
> > > 
> > > And you also can't stop drm_sched to prevent races?  
> > 
> > That's the thing, I don't want to stop the drm_gpu_scheduler attached
> > to a panthor_queue, I want new jobs to be queued to the ring buffer
> > until this ring buffer is full (which is controller with the
> > ::credit_limit property), even if the group this queue belongs to is
> > not currently active on the FW side. Those jobs will get executed at
> > some later point when the group gets picked by the panthor scheduler.  
> 
> Ah, OK! Understood.
> 
> > > 
> > > As you know I only learned a few weeks ago about your group scheduler
> > > on top of drm_sched. I wish I had heard about it when it was
> > > implemented; we might have come up with the idea for drm_jobqueue
> > > sooner.  
> > 
> > Might have simplified things, I guess, but that's life, and I'm happy
> > to transition to drm_jobqueue when it's deemed ready.  
> 
> JQ is in Rust, potentially one day with a C ABI. So that could only
> happen if your driver's users are OK with relying on LLVM for building
> the kernel.
> 
> BTW would be interesting for me to know to what degree that's a problem
> for common distributions and users.

That's a good question. I must admit I never thought of this because I
usually build my kernels on a full-blown distro with both llvm and gcc
installed, so I can easily pick the one I need for the task. For distro
builds that should be okay, but for {yocto,buildroot,custom}-based
build systems the transition might be painful/annoying, but I'd expect
people to move to llvm if they have to. I mean, the ultimate goal is
for Tyr to replace Panthor so we don't have to maintain two drivers, so
if that's going to be a problem, I'd rather know it now :-).