linux-kernel - Re: [PATCH v4 2/2] media: uvcvideo: Do power management granularly

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Date:   Tue, 6 Dec 2022 10:51:45 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Ricardo Ribalda <ribalda@...omium.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, Yunke Cao <yunkec@...omium.org>,
        Max Staudt <mstaudt@...omium.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Alan Stern <stern@...land.harvard.edu>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] media: uvcvideo: Do power management granularly

On (22/12/02 18:19), Ricardo Ribalda wrote:
>  /* ------------------------------------------------------------------------
>   * UVC ioctls
>   */
> @@ -249,6 +289,9 @@ static int uvc_v4l2_try_format(struct uvc_streaming *stream,
>  	 * developers test their webcams with the Linux driver as well as with
>  	 * the Windows driver).
>  	 */
> +	ret = uvc_pm_get(stream);
> +	if (ret)
> +		return ret;
>  	mutex_lock(&stream->mutex);

So here we acquire stream->dev->lock outside of stream->mutex scope

>  	if (stream->dev->quirks & UVC_QUIRK_PROBE_EXTRAFIELDS)
>  		probe->dwMaxVideoFrameSize =
> @@ -257,6 +300,7 @@ static int uvc_v4l2_try_format(struct uvc_streaming *stream,
>  	/* Probe the device. */
>  	ret = uvc_probe_video(stream, probe);
>  	mutex_unlock(&stream->mutex);
> +	uvc_pm_put(stream);
>  	if (ret < 0)
>  		return ret;

[..]

> @@ -468,7 +512,13 @@ static int uvc_v4l2_set_streamparm(struct uvc_streaming *stream,
>  	}
>  
>  	/* Probe the device with the new settings. */
> +	ret = uvc_pm_get(stream);
> +	if (ret) {
> +		mutex_unlock(&stream->mutex);
> +		return ret;
> +	}
>  	ret = uvc_probe_video(stream, &probe);
> +	uvc_pm_put(stream);
>  	if (ret < 0) {
>  		mutex_unlock(&stream->mutex);
>  		return ret;

But here we nest and grab stream->dev->lock under stream->mutex.
Is this nesting intentional?