linux-kernel - Re: [PATCH v3 4/9] media: subdev: Fix use of sd->enabled_streams in call_s

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Message-ID: <a808c81c-2006-410e-ba8c-74c5405acbdf@ideasonboard.com>
Date: Thu, 11 Apr 2024 10:46:33 +0530
From: Umang Jain <umang.jain@...asonboard.com>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>, Hans Verkuil
 <hverkuil@...all.nl>, Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/9] media: subdev: Fix use of sd->enabled_streams in
 call_s_stream()

Hi Tomi,

Thank you for the patch

On 10/04/24 6:05 pm, Tomi Valkeinen wrote:
> call_s_stream() uses sd->enabled_streams to track whether streaming has
> already been enabled. However,
> v4l2_subdev_enable/disable_streams_fallback(), which was the original
> user of this field, already uses it, and
> v4l2_subdev_enable/disable_streams_fallback() will call call_s_stream().
>
> This leads to a conflict as both functions set the field. Afaics, both
> functions set the field to the same value, so it won't cause a runtime
> bug, but it's still wrong and if we, e.g., change how
> v4l2_subdev_enable/disable_streams_fallback() operates we might easily
> cause bugs.
>
> Fix this by adding a new field, 'streaming_enabled', for
> call_s_stream().

Just a suggestion, as this is only used in call_s_stream(), maybe naming 
this field 's_stream_enabled' ?

Rest looks good to me,

Reviewed-by: Umang Jain <umang.jain@...asonboard.com>

>
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
> ---
>   drivers/media/v4l2-core/v4l2-subdev.c | 8 ++------
>   include/media/v4l2-subdev.h           | 3 +++
>   2 files changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> index 606a909cd778..6cd353d83dfc 100644
> --- a/drivers/media/v4l2-core/v4l2-subdev.c
> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> @@ -421,12 +421,8 @@ static int call_s_stream(struct v4l2_subdev *sd, int enable)
>   	 * The .s_stream() operation must never be called to start or stop an
>   	 * already started or stopped subdev. Catch offenders but don't return
>   	 * an error yet to avoid regressions.
> -	 *
> -	 * As .s_stream() is mutually exclusive with the .enable_streams() and
> -	 * .disable_streams() operation, we can use the enabled_streams field
> -	 * to store the subdev streaming state.
>   	 */
> -	if (WARN_ON(!!sd->enabled_streams == !!enable))
> +	if (WARN_ON(sd->streaming_enabled == !!enable))
>   		return 0;
>   
>   	ret = sd->ops->video->s_stream(sd, enable);
> @@ -437,7 +433,7 @@ static int call_s_stream(struct v4l2_subdev *sd, int enable)
>   	}
>   
>   	if (!ret) {
> -		sd->enabled_streams = enable ? BIT(0) : 0;
> +		sd->streaming_enabled = enable;
>   
>   		if (enable)
>   			v4l2_subdev_enable_privacy_led(sd);
> diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
> index a9e6b8146279..f55d03e0acc1 100644
> --- a/include/media/v4l2-subdev.h
> +++ b/include/media/v4l2-subdev.h
> @@ -1043,6 +1043,8 @@ struct v4l2_subdev_platform_data {
>    *		     v4l2_subdev_enable_streams() and
>    *		     v4l2_subdev_disable_streams() helper functions for fallback
>    *		     cases.
> + * @streaming_enabled: Tracks whether streaming has been enabled with s_stream.
> + *                     This is only for call_s_stream() internal use.
>    *
>    * Each instance of a subdev driver should create this struct, either
>    * stand-alone or embedded in a larger struct.
> @@ -1091,6 +1093,7 @@ struct v4l2_subdev {
>   	 */
>   	struct v4l2_subdev_state *active_state;
>   	u64 enabled_streams;
> +	bool streaming_enabled;
>   };
>   
>   
>