[PATCH v15 14/15] drm/panfrost: Introduce a reset lock

[Adrián Larumbe]

In order 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 timestamp.

Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>
Reviewed-by: Steven Price <steven.price@xxxxxxx>
Signed-off-by: Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx>
---
 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 b3dae6ce3eb0..5718e8185427 100644
--- a/drivers/gpu/drm/panfrost/panfrost_device.c
+++ b/drivers/gpu/drm/panfrost/panfrost_device.c
@@ -509,6 +509,8 @@ bool panfrost_exception_needs_reset(const struct panfrost_device *pfdev,
 
 void panfrost_device_reset(struct panfrost_device *pfdev, bool enable_job_int)
 {
+	guard(rwsem_write)(&pfdev->reset.lock);
+
 	panfrost_gpu_soft_reset(pfdev);
 
 	panfrost_gpu_power_on(pfdev);
diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
index a0b9a2145fc9..63452febb1cf 100644
--- a/drivers/gpu/drm/panfrost/panfrost_device.h
+++ b/drivers/gpu/drm/panfrost/panfrost_device.h
@@ -165,6 +165,7 @@ 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 da10eee85ca2..a141a41e224b 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 ab65786bf63b..4ddf4b722ddf 100644
--- a/drivers/gpu/drm/panfrost/panfrost_job.c
+++ b/drivers/gpu/drm/panfrost/panfrost_job.c
@@ -877,6 +877,7 @@ int panfrost_jm_init(struct panfrost_device *pfdev)
 	INIT_WORK(&pfdev->reset.work, panfrost_reset_work);
 	spin_lock_init(&js->job_lock);
 	mutex_init(&pfdev->sched_lock);
+	init_rwsem(&pfdev->reset.lock);
 
 	js->irq = platform_get_irq_byname(to_platform_device(pfdev->base.dev), "job");
 	if (js->irq < 0)

-- 
2.55.0