linux-kernel - Re: [PATCH v3 1/6] media: uvcvideo: Keep streaming state in the file handle

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Message-ID: <20250223154617.GB27463@pendragon.ideasonboard.com>
Date: Sun, 23 Feb 2025 17:46:17 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Ricardo Ribalda <ribalda@...omium.org>
Cc: Hans de Goede <hdegoede@...hat.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Guennadi Liakhovetski <guennadi.liakhovetski@...el.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab+samsung@...nel.org>
Subject: Re: [PATCH v3 1/6] media: uvcvideo: Keep streaming state in the file
 handle

Hi Ricardo,

Thank you for the patch.

On Thu, Feb 06, 2025 at 07:47:00PM +0000, Ricardo Ribalda wrote:
> Add a variable in the file handle state to figure out if a camera is in
> the streaming state or not.

s/\n/ / (and reflow) or s/$/\n/ depending on what you meant.

> This variable will be used in the future for power management policies.
> 
> Now that we are at it, make use of guards to simplify the code.
> 
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
>  drivers/media/usb/uvc/uvc_v4l2.c | 15 +++++++++++----
>  drivers/media/usb/uvc/uvcvideo.h |  1 +
>  2 files changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> index 93c6cdb23881..856eaa23e703 100644
> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> @@ -835,11 +835,17 @@ static int uvc_ioctl_streamon(struct file *file, void *fh,
>  	if (!uvc_has_privileges(handle))
>  		return -EBUSY;
>  
> -	mutex_lock(&stream->mutex);
> +	guard(mutex)(&stream->mutex);
> +
> +	if (handle->is_streaming)
> +		return 0;
> +
>  	ret = uvc_queue_streamon(&stream->queue, type);
> -	mutex_unlock(&stream->mutex);
> +	if (!ret)
> +		handle->is_streaming = true;
>  
>  	return ret;

Now that you use a mutex guard, you can write

	if (ret)
		return ret;

	handle->is_streaming = true;
	return 0;

apart from that,

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> +
>  }
>  
>  static int uvc_ioctl_streamoff(struct file *file, void *fh,
> @@ -851,9 +857,10 @@ static int uvc_ioctl_streamoff(struct file *file, void *fh,
>  	if (!uvc_has_privileges(handle))
>  		return -EBUSY;
>  
> -	mutex_lock(&stream->mutex);
> +	guard(mutex)(&stream->mutex);
> +
>  	uvc_queue_streamoff(&stream->queue, type);
> -	mutex_unlock(&stream->mutex);
> +	handle->is_streaming = false;
>  
>  	return 0;
>  }
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index 5e388f05f3fc..bc87e1f2c669 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -618,6 +618,7 @@ struct uvc_fh {
>  	struct uvc_streaming *stream;
>  	enum uvc_handle_state state;
>  	unsigned int pending_async_ctrls;
> +	bool is_streaming;
>  };
>  
>  struct uvc_driver {

-- 
Regards,

Laurent Pinchart