[PATCH v2] drm/panthor: Serialize GPU cache flush operations

[Karunika Choo]

In certain scenarios, it is possible for multiple cache flushes to be
requested before the previous one completes. This patch introduces the
cache_flush_lock mutex to serialize these operations and ensure that
any requested cache flushes are completed instead of dropped.

Reviewed-by: Liviu Dudau <liviu.dudau at arm.com>
Co-developed-by: Dennis Tsiang <dennis.tsiang at arm.com>
Signed-off-by: Dennis Tsiang <dennis.tsiang at arm.com>
Signed-off-by: Karunika Choo <karunika.choo at arm.com>
---
v2:
- Added missing 'Signed-off-by' for Dennis.
- Picked up R-b from Liviu.
- Link to v1: https://lore.kernel.org/all/20250730174338.1650212-1-karunika.choo@arm.com/

 drivers/gpu/drm/panthor/panthor_gpu.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/panthor/panthor_gpu.c b/drivers/gpu/drm/panthor/panthor_gpu.c
index cb7a335e07d7..030409371037 100644
--- a/drivers/gpu/drm/panthor/panthor_gpu.c
+++ b/drivers/gpu/drm/panthor/panthor_gpu.c
@@ -35,6 +35,9 @@ struct panthor_gpu {
 
 	/** @reqs_acked: GPU request wait queue. */
 	wait_queue_head_t reqs_acked;
+
+	/** @cache_flush_lock: Lock to serialize cache flushes */
+	struct mutex cache_flush_lock;
 };
 
 /**
@@ -204,6 +207,7 @@ int panthor_gpu_init(struct panthor_device *ptdev)
 
 	spin_lock_init(&gpu->reqs_lock);
 	init_waitqueue_head(&gpu->reqs_acked);
+	mutex_init(&gpu->cache_flush_lock);
 	ptdev->gpu = gpu;
 	panthor_gpu_init_info(ptdev);
 
@@ -353,6 +357,9 @@ int panthor_gpu_flush_caches(struct panthor_device *ptdev,
 	bool timedout = false;
 	unsigned long flags;
 
+	/* Serialize cache flush operations. */
+	guard(mutex)(&ptdev->gpu->cache_flush_lock);
+
 	spin_lock_irqsave(&ptdev->gpu->reqs_lock, flags);
 	if (!drm_WARN_ON(&ptdev->base,
 			 ptdev->gpu->pending_reqs & GPU_IRQ_CLEAN_CACHES_COMPLETED)) {
-- 
2.49.0