linux-kernel - Re: [PATCH] drm/panthor: always set fence errors on CS

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Message-ID: <CAPaKu7TTR4prUqt=AL2Lh=od9B_RqQpH+5redvFb3FY749Ebgg@mail.gmail.com>
Date: Tue, 8 Jul 2025 14:40:06 -0700
From: Chia-I Wu <olvaffe@...il.com>
To: Boris Brezillon <boris.brezillon@...labora.com>
Cc: Steven Price <steven.price@....com>, Liviu Dudau <liviu.dudau@....com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panthor: always set fence errors on CS_FAULT

On Sun, Jun 22, 2025 at 11:32 PM Boris Brezillon
<boris.brezillon@...labora.com> wrote:
>
> On Wed, 18 Jun 2025 07:55:49 -0700
> Chia-I Wu <olvaffe@...il.com> wrote:
>
> > It is unclear why fence errors were set only for CS_INHERIT_FAULT.
> > Downstream driver also does not treat CS_INHERIT_FAULT specially.
> > Remove the check.
> >
> > Signed-off-by: Chia-I Wu <olvaffe@...il.com>
> > ---
> >  drivers/gpu/drm/panthor/panthor_sched.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> > index a2248f692a030..1a3b1c49f7d7b 100644
> > --- a/drivers/gpu/drm/panthor/panthor_sched.c
> > +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> > @@ -1399,7 +1399,7 @@ cs_slot_process_fault_event_locked(struct panthor_device *ptdev,
> >       fault = cs_iface->output->fault;
> >       info = cs_iface->output->fault_info;
> >
> > -     if (queue && CS_EXCEPTION_TYPE(fault) == DRM_PANTHOR_EXCEPTION_CS_INHERIT_FAULT) {
> > +     if (queue) {
> >               u64 cs_extract = queue->iface.output->extract;
> >               struct panthor_job *job;
> >
>
> Now that I look at the code, I think we should record the error when
> the ERROR_BARRIER is executed instead of flagging all in-flight jobs as
> faulty. One option would be to re-use the profiling buffer by adding an
> error field to panthor_job_profiling_data, but we're going to lose 4
> bytes per slot because of the 64-bit alignment we want for timestamps,
> so maybe just create a separate buffers with N entries of:
>
> struct panthor_job_status {
>    u32 error;
> };
The current error path uses cs_extract to mark exactly the offending
job faulty.  Innocent in-flight jobs do not seem to be affected.

I looked into emitting LOAD/STORE after SYNC_ADD64 to copy the error
to panthor_job_status.  Other than the extra instrs and storage,
because group_sync_upd_work can be called before LOAD/STORE, it will
need to check both panthor_job_status and panthor_syncobj_64b.  That
will be a bit ugly as well.