Re: [PATCH v5 09/11] drm/panfrost: Introduce a reset lock

["Adrián Larumbe" <adrian.larumbe@collabora.com>]

On 12.08.2026 11:45, Boris Brezillon wrote:
> On Tue, 11 Aug 2026 22:42:18 +0100
> Adrián Larumbe <adrian.larumbe@collabora.com> wrote:
> 
> > So as to avoid accessing HW register while a reset is ongoing, a read/write
> > semaphore that envelopes the reset sequence will help driver entry points
> > avoid racing with it. For now, the only such racy entry point is the ioctl
> > that returns the current GPU timestmap.
> > 
> > Signed-off-by: Adrián Larumbe <adrian.larumbe@collabora.com>
> > ---
> >  drivers/gpu/drm/panfrost/panfrost_device.c | 2 ++
> >  drivers/gpu/drm/panfrost/panfrost_device.h | 1 +
> >  drivers/gpu/drm/panfrost/panfrost_drv.c    | 9 ++++++---
> >  drivers/gpu/drm/panfrost/panfrost_job.c    | 1 +
> >  4 files changed, 10 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
> > index 5b66173c75b9..e0390b6c0d22 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_device.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_device.c
> > @@ -602,6 +602,8 @@ bool panfrost_exception_needs_reset(const struct panfrost_device *pfdev,
> >  
> >  void panfrost_device_reset(struct panfrost_device *pfdev, bool enable_job_int)
> >  {
> > +	guard(rwsem_read)(&pfdev->reset.lock);
> 
> Oops, s/rwsem_read/rwsem_write/. This is actually fixed in the next
> patch.

Sorry about this, I seemed to have botched the final interactive rebase.

> > +
> >  	panfrost_gpu_soft_reset(pfdev);
> >  	panfrost_gpu_power_on(pfdev);
> >  	panfrost_mmu_reset(pfdev);
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
> > index 4bbaaaf827a5..a2a68e042225 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_device.h
> > +++ b/drivers/gpu/drm/panfrost/panfrost_device.h
> > @@ -166,6 +166,7 @@ struct panfrost_device {
> >  	struct {
> >  		struct workqueue_struct *wq;
> >  		struct work_struct work;
> > +		struct rw_semaphore lock;
> >  		atomic_t pending;
> >  	} reset;
> >  
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
> > index 958f1d36ab10..ff23b1a979bb 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_drv.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c
> > @@ -41,9 +41,12 @@ static int panfrost_ioctl_query_timestamp(struct panfrost_device *pfdev,
> >  	if (ret)
> >  		return ret;
> >  
> > -	panfrost_cycle_counter_get(pfdev);
> > -	*arg = panfrost_timestamp_read(pfdev);
> > -	panfrost_cycle_counter_put(pfdev);
> > +	/* We should not read timestamp register while the GPU  is being reset */
> > +	scoped_guard(rwsem_read, &pfdev->reset.lock) {
> > +		panfrost_cycle_counter_get(pfdev);
> > +		*arg = panfrost_timestamp_read(pfdev);
> > +		panfrost_cycle_counter_put(pfdev);
> > +	}
> >  
> >  	pm_runtime_put(pfdev->base.dev);
> >  	return 0;
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
> > index c761379851da..9d7dafa29f19 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> > +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> > @@ -874,6 +874,7 @@ int panfrost_jm_init(struct panfrost_device *pfdev)
> >  
> >  	INIT_WORK(&pfdev->reset.work, panfrost_reset_work);
> >  	spin_lock_init(&js->job_lock);
> > +	init_rwsem(&pfdev->reset.lock);
> >  
> >  	js->irq = platform_get_irq_byname(to_platform_device(pfdev->base.dev), "job");
> >  	if (js->irq < 0)
> > 

Adrian Larumbe