linux-kernel - Re: [PATCH v6 5/5] media: uvcvideo: Flush the control cache when we get an event

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Message-ID: <02a89566-a6f7-4feb-84c3-079795c98a46@redhat.com>
Date: Mon, 9 Dec 2024 12:03:50 +0100
From: Hans de Goede <hdegoede@...hat.com>
To: Ricardo Ribalda <ribalda@...omium.org>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>,
 Guennadi Liakhovetski <guennadi.liakhovetski@...el.com>
Cc: Hans Verkuil <hverkuil@...all.nl>,
 Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
 linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 5/5] media: uvcvideo: Flush the control cache when we
 get an event

Hi Ricardo,

On 3-Dec-24 10:20 PM, Ricardo Ribalda wrote:
> Asynchronous controls trigger an event when they have completed their
> operation.
> 
> This can make that the control cached value does not match the value in
> the device.
> 
> Let's flush the cache to be on the safe side.
> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>

Thank you for your patch.

It seems that you have missed Laurent's reply asking to improve the commit message:

"Conceptually this change looks fine, but the commit message needs to
explain why this is safe to do without protecting ctrl->loaded with a
lock."

https://lore.kernel.org/linux-media/20241203203748.GD5196@pendragon.ideasonboard.com/

Or maybe the posting of this v6 and that reply have crossed each other.

Either way please post a new version addressing this comment.

Thanks & Regards,

Hans



> ---
>  drivers/media/usb/uvc/uvc_ctrl.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> index 3dc9b7a49f64..db29e0e8bfd4 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -1622,6 +1622,9 @@ void uvc_ctrl_status_event(struct uvc_video_chain *chain,
>  
>  	mutex_lock(&chain->ctrl_mutex);
>  
> +	/* Flush the control cache, the data might have changed. */
> +	ctrl->loaded = 0;
> +
>  	handle = ctrl->handle;
>  	if (handle)
>  		uvc_ctrl_set_handle(handle, ctrl, NULL);
>