[PATCH 3/4] media: uvcvideo: synchronize imported DMA-BUFs for CPU access

[Karl Mehltretter]

uvcvideo writes USB payloads into imported DMA-BUFs with the CPU without
cache synchronization, leaving physical RAM stale.

Set uses_cpu_access to bracket the driver's CPU access.

On a Pi 400, 12 eight-frame captures each had stale data before this
change. All 96 frames matched RAM with it.

Fixes: ccc4c539c05f ("[media] v4l: uvc: add support for DMABUF importing")
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <kmehltretter@xxxxxxxxx>
---
 drivers/media/usb/uvc/uvc_queue.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/media/usb/uvc/uvc_queue.c b/drivers/media/usb/uvc/uvc_queue.c
index 3c002c8f442fb..1f92ee96e0710 100644
--- a/drivers/media/usb/uvc/uvc_queue.c
+++ b/drivers/media/usb/uvc/uvc_queue.c
@@ -247,6 +247,7 @@ int uvc_queue_init(struct uvc_streaming *stream, struct uvc_video_queue *queue,
 	queue->queue.drv_priv = queue;
 	queue->queue.buf_struct_size = sizeof(struct uvc_buffer);
 	queue->queue.mem_ops = &vb2_vmalloc_memops;
+	queue->queue.uses_cpu_access = true;
 	queue->queue.timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC
 		| V4L2_BUF_FLAG_TSTAMP_SRC_SOE;
 	queue->queue.lock = &queue->mutex;
-- 
2.47.3