On 12.08.2026 11:45, Boris Brezillon wrote:
> On Tue, 11 Aug 2026 22:42:18 +0100
> Adrián Larumbe <[email protected]> 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 <[email protected]>
> > ---
> > 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
