drm/panthor: Serialize GPU cache flush operations

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@arm.com>
Co-developed-by: Dennis Tsiang <dennis.tsiang@arm.com>
Signed-off-by: Dennis Tsiang <dennis.tsiang@arm.com>
Signed-off-by: Karunika Choo <karunika.choo@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://lore.kernel.org/r/20250807162633.3666310-6-karunika.choo@arm.com

diff --git a/drivers/gpu/drm/panthor/panthor_gpu.c b/drivers/gpu/drm/panthor/panthor_gpu.c
index 5e2c3173ae27f13d31fb4b5c101e3585dfe8a038..db69449a5be0994bdc39c8e32fa9694360805dc3 100644 (file)
--- 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;
 };
 
 #define GPU_INTERRUPTS_MASK    \
@@ -110,6 +113,7 @@ 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;
 
        dma_set_max_seg_size(ptdev->base.dev, UINT_MAX);
@@ -258,6 +262,9 @@ 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)) {