Re: [PATCH 2/4] media: subdev: Fix use of sd->enabled_streams in call_s_stream()

Laurent Pinchart
2024-04-04T13:00:36Z

Hi Tomi,

Thank you for the patch.

On Thu, Apr 04, 2024 at 01:50:01PM +0300, 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().
>
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
> ---
> drivers/media/v4l2-core/v4l2-subdev.c | 8 ++------
> include/media/v4l2-subdev.h | 2 ++
> 2 files changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> index b90b5185e87f..3b3310bce5d4 100644
> --- a/drivers/media/v4l2-core/v4l2-subdev.c
> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> @@ -404,12 +404,8 @@ 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;
>
> #if IS_REACHABLE(CONFIG_LEDS_CLASS)
> @@ -429,7 +425,7 @@ static int call_s_stream(struct v4l2_subdev *sd, int enable)
> }
>
> if (!ret)
> - sd->enabled_streams = enable ? BIT(0) : 0;
> + sd->streaming_enabled = !!enable;
>
> return ret;
> }
> diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
> index a9e6b8146279..8bd1e3c96d2b 100644
> --- a/include/media/v4l2-subdev.h
> +++ b/include/media/v4l2-subdev.h
> @@ -1043,6 +1043,7 @@ 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.

Could you extend this to indicate this field can't be used by anything
else than call_s_stream() ?

I'm also getting a bit concerned about having multiple fields with
similar purposes. Another option would be to call the .s_stream()
operation directly from the fallback handlers, instead of going through
call_s_stream(). That may be considered as a bit of a hack though.

> *
> * Each instance of a subdev driver should create this struct, either
> * stand-alone or embedded in a larger struct.
> @@ -1091,6 +1092,7 @@ struct v4l2_subdev {
> */
> struct v4l2_subdev_state *active_state;
> u64 enabled_streams;
> + bool streaming_enabled;
> };
>
>

--
Regards,

Laurent Pinchart