[PATCH] staging: most: video: document the locks in struct most_video_dev

[PATCH] staging: most: video: document the locks in struct most_video_dev

[Godana Emiru]

Neither lock in struct most_video_dev carries a comment describing what
it protects.

list_lock protects the pending_mbos list. Buffers are added by the
component's rx_completion callback, comp_rx_data(), which is invoked
from the interface driver's completion path (a URB completion handler
in the case of the USB HDM), and are removed from process context by
comp_vdev_read() and comp_vdev_close(). Note that in the comment, since
it is what makes the irq-safe spinlock variants necessary here.

lock is never acquired by this driver directly. comp_register_videodev()
installs it as struct video_device::lock, where v4l2_ioctl_get_lock()
returns it and video_ioctl2() holds it across ioctl dispatch.

No functional change.

Signed-off-by: Godana Emiru <godanaemiru@gmail.com>
---
 drivers/staging/most/video/video.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/staging/most/video/video.c b/drivers/staging/most/video/video.c
index 88892b5db..c354d1820 100644
--- a/drivers/staging/most/video/video.c
+++ b/drivers/staging/most/video/video.c
@@ -33,6 +33,7 @@ struct most_video_dev {
 	bool mute;
 
 	struct list_head pending_mbos;
+	/* protects pending_mbos; taken from rx completion (softirq) */
 	spinlock_t list_lock;
 
 	struct v4l2_device v4l2_dev;
@@ -40,6 +41,7 @@ struct most_video_dev {
 	struct video_device *vdev;
 	unsigned int ctrl_input;
 
+	/* serializes V4L2 ioctls; used as struct video_device::lock */
 	struct mutex lock;
 
 	wait_queue_head_t wait_data;
-- 
2.53.0

Re: [PATCH] staging: most: video: document the locks in struct most_video_dev

[Greg KH]

On Tue, Sep 01, 2026 at 08:20:55PM +0300, Godana Emiru wrote:
> Neither lock in struct most_video_dev carries a comment describing what
> it protects.
> 
> list_lock protects the pending_mbos list. Buffers are added by the
> component's rx_completion callback, comp_rx_data(), which is invoked
> from the interface driver's completion path (a URB completion handler
> in the case of the USB HDM), and are removed from process context by
> comp_vdev_read() and comp_vdev_close(). Note that in the comment, since
> it is what makes the irq-safe spinlock variants necessary here.
> 
> lock is never acquired by this driver directly. comp_register_videodev()
> installs it as struct video_device::lock, where v4l2_ioctl_get_lock()
> returns it and video_ioctl2() holds it across ioctl dispatch.

What tool did you use to generate this changelog?

thanks,

greg k-h

Re: [PATCH] staging: most: video: document the locks in struct most_video_dev

[Godana Emiru]

Hi Greg,
I used an LLM (Claude) to help trace the locking and draft the changelog
for this patch. I reviewed it and sent it under my own Signed-off-by, but
I failed to add the "Assisted-by: LLM" tag required by
Documentation/process/coding-assistants.rst. The same applies to my
earlier rtl8723bs patch. I apologize for the omission.

I'm happy to resend with the correct tags if the patches are otherwise
useful, or drop them if you prefer.

thanks,
Godana