Re: [PATCH v3 4/9] media: subdev: Fix use of sd->enabled_streams in call_s_stream()

[Tomi Valkeinen]

On 11/04/2024 08:16, Umang Jain wrote:
> 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' ?

Yes, I think that's a good idea.

 Tomi

> Rest looks good to me,
>
> Reviewed-by: Umang Jain <umang.jain@xxxxxxxxxxxxxxxx>
>
> > Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
> > ---
> >   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;
> >   };