[PATCH v3 11/13] drm/panfrost: Introduce a reset lock

[Adrián Larumbe]

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@xxxxxxxxxxxxx>
---
 drivers/gpu/drm/panfrost/panfrost_device.c | 5 +++++
 drivers/gpu/drm/panfrost/panfrost_device.h | 1 +
 drivers/gpu/drm/panfrost/panfrost_drv.c    | 9 ++++++---
 drivers/gpu/drm/panfrost/panfrost_job.c    | 2 ++
 4 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_device.c b/drivers/gpu/drm/panfrost/panfrost_device.c
index 80746e375410..46c6e911e562 100644
--- a/drivers/gpu/drm/panfrost/panfrost_device.c
+++ b/drivers/gpu/drm/panfrost/panfrost_device.c
@@ -617,6 +617,10 @@ void panfrost_device_reset(struct panfrost_device *pfdev, bool enable_job_int)
 {
 	int ret;
 
+	/* Pre-reset */
+	if (panfrost_device_is_initialized(pfdev))
+		down_write(&pfdev->reset.lock);
+
 	/* Do the actual device reset */
 	ret = panfrost_gpu_soft_reset(pfdev);
 	panfrost_gpu_power_on(pfdev);
@@ -630,6 +634,7 @@ void panfrost_device_reset(struct panfrost_device *pfdev, bool enable_job_int)
 		panfrost_jm_reset_interrupts(pfdev);
 		if (enable_job_int)
 			panfrost_jm_enable_interrupts(pfdev);
+		up_write(&pfdev->reset.lock);
 	}
 }
 
diff --git a/drivers/gpu/drm/panfrost/panfrost_device.h b/drivers/gpu/drm/panfrost/panfrost_device.h
index 855ee4d0fb40..7f5202ff6469 100644
--- a/drivers/gpu/drm/panfrost/panfrost_device.h
+++ b/drivers/gpu/drm/panfrost/panfrost_device.h
@@ -167,6 +167,7 @@ struct panfrost_device {
 	struct {
 		struct workqueue_struct *wq;
 		struct work_struct work;
+		struct rw_semaphore lock;
 		wait_queue_head_t wait;
 		atomic_t pending;
 	} reset;
diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c b/drivers/gpu/drm/panfrost/panfrost_drv.c
index 2490e9785057..e04eb416ea0f 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 c2a1670a74e8..c1d0b111dde1 100644
--- a/drivers/gpu/drm/panfrost/panfrost_job.c
+++ b/drivers/gpu/drm/panfrost/panfrost_job.c
@@ -895,7 +895,9 @@ int panfrost_jm_init(struct panfrost_device *pfdev)
 	if (!pfdev->reset.wq)
 		return -ENOMEM;
 	args.timeout_wq = pfdev->reset.wq;
+
 	init_waitqueue_head(&pfdev->reset.wait);
+	init_rwsem(&pfdev->reset.lock);
 
 	for (j = 0; j < NUM_JOB_SLOTS; j++) {
 		js->queue[j].fence_context = dma_fence_context_alloc(1);

-- 
2.55.0