[PATCH 1/2] media: v4l2-subdev: Provide const-aware subdev state accessors
Sakari Ailus
sakari.ailus at iki.fi
Mon May 6 14:53:18 PDT 2024
Hi Laurent,
Thanks for the patch.
On Mon, May 06, 2024 at 08:52:54PM +0300, Laurent Pinchart wrote:
> It would be useful to mark instances of v4l2_subdev_state structures as
> const when code needs to access them read-only. This isn't currently
> possible, as the v4l2_subdev_state_get_*() accessor functions take a
> non-const pointer to the state.
>
> Use _Generic() to provide two different versions of the accessors, for
> const and non-const states respectively. The former returns a const
> pointer to the requested format, rectangle or interval, implementing
> const-correctness. The latter returns a non-const pointer, preserving
> the current behaviour for drivers.
>
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas at ideasonboard.com>
> ---
> Bike-shedding about names and the 4 leading underscores is allowed (and
> expected).
> ---
> drivers/media/v4l2-core/v4l2-subdev.c | 24 +++++-----
> include/media/v4l2-subdev.h | 66 ++++++++++++++++++---------
> 2 files changed, 57 insertions(+), 33 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> index 83c6d1e36871..af1fbc28c8f0 100644
> --- a/drivers/media/v4l2-core/v4l2-subdev.c
> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> @@ -1616,8 +1616,8 @@ void v4l2_subdev_cleanup(struct v4l2_subdev *sd)
> EXPORT_SYMBOL_GPL(v4l2_subdev_cleanup);
>
> struct v4l2_mbus_framefmt *
> -__v4l2_subdev_state_get_format(struct v4l2_subdev_state *state,
> - unsigned int pad, u32 stream)
> +____v4l2_subdev_state_get_format(struct v4l2_subdev_state *state,
> + unsigned int pad, u32 stream)
> {
> struct v4l2_subdev_stream_configs *stream_configs;
> unsigned int i;
> @@ -1647,11 +1647,11 @@ __v4l2_subdev_state_get_format(struct v4l2_subdev_state *state,
>
> return NULL;
> }
> -EXPORT_SYMBOL_GPL(__v4l2_subdev_state_get_format);
> +EXPORT_SYMBOL_GPL(____v4l2_subdev_state_get_format);
>
> struct v4l2_rect *
> -__v4l2_subdev_state_get_crop(struct v4l2_subdev_state *state, unsigned int pad,
> - u32 stream)
> +____v4l2_subdev_state_get_crop(struct v4l2_subdev_state *state, unsigned int pad,
> + u32 stream)
> {
> struct v4l2_subdev_stream_configs *stream_configs;
> unsigned int i;
> @@ -1681,11 +1681,11 @@ __v4l2_subdev_state_get_crop(struct v4l2_subdev_state *state, unsigned int pad,
>
> return NULL;
> }
> -EXPORT_SYMBOL_GPL(__v4l2_subdev_state_get_crop);
> +EXPORT_SYMBOL_GPL(____v4l2_subdev_state_get_crop);
>
> struct v4l2_rect *
> -__v4l2_subdev_state_get_compose(struct v4l2_subdev_state *state,
> - unsigned int pad, u32 stream)
> +____v4l2_subdev_state_get_compose(struct v4l2_subdev_state *state,
> + unsigned int pad, u32 stream)
> {
> struct v4l2_subdev_stream_configs *stream_configs;
> unsigned int i;
> @@ -1715,11 +1715,11 @@ __v4l2_subdev_state_get_compose(struct v4l2_subdev_state *state,
>
> return NULL;
> }
> -EXPORT_SYMBOL_GPL(__v4l2_subdev_state_get_compose);
> +EXPORT_SYMBOL_GPL(____v4l2_subdev_state_get_compose);
>
> struct v4l2_fract *
> -__v4l2_subdev_state_get_interval(struct v4l2_subdev_state *state,
> - unsigned int pad, u32 stream)
> +____v4l2_subdev_state_get_interval(struct v4l2_subdev_state *state,
> + unsigned int pad, u32 stream)
> {
> struct v4l2_subdev_stream_configs *stream_configs;
> unsigned int i;
> @@ -1751,7 +1751,7 @@ __v4l2_subdev_state_get_interval(struct v4l2_subdev_state *state,
>
> return NULL;
> }
> -EXPORT_SYMBOL_GPL(__v4l2_subdev_state_get_interval);
> +EXPORT_SYMBOL_GPL(____v4l2_subdev_state_get_interval);
>
> #if defined(CONFIG_VIDEO_V4L2_SUBDEV_API)
>
> diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
> index e30c463d90e5..ba722ab501c1 100644
> --- a/include/media/v4l2-subdev.h
> +++ b/include/media/v4l2-subdev.h
> @@ -1340,21 +1340,27 @@ void v4l2_subdev_cleanup(struct v4l2_subdev *sd);
> */
> /*
> * Wrap v4l2_subdev_state_get_format(), allowing the function to be called with
> - * two or three arguments. The purpose of the __v4l2_subdev_state_get_format()
> + * two or three arguments. The purpose of the __v4l2_subdev_state_gen_call()
> * macro below is to come up with the name of the function or macro to call,
> * using the last two arguments (_stream and _pad). The selected function or
> * macro is then called using the arguments specified by the caller. A similar
> * arrangement is used for v4l2_subdev_state_crop() and
> * v4l2_subdev_state_compose() below.
> */
> -#define v4l2_subdev_state_get_format(state, pad, ...) \
> - __v4l2_subdev_state_gen_call(format, ##__VA_ARGS__, , _pad) \
> +#define v4l2_subdev_state_get_format(state, pad, ...) \
> + __v4l2_subdev_state_gen_call(format, ##__VA_ARGS__, , _pad) \
> (state, pad, ##__VA_ARGS__)
> -#define __v4l2_subdev_state_get_format_pad(state, pad) \
> +#define __v4l2_subdev_state_get_format_pad(state, pad) \
> __v4l2_subdev_state_get_format(state, pad, 0)
> +#define __v4l2_subdev_state_get_format(state, pad, stream) \
> + _Generic(state, \
> + const struct v4l2_subdev_state *: ((const struct v4l2_mbus_framefmt *) \
> + ____v4l2_subdev_state_get_format((struct v4l2_subdev_state *)state, pad, stream)), \
> + default: ____v4l2_subdev_state_get_format((struct v4l2_subdev_state *)state, pad, stream) \
> + )
> struct v4l2_mbus_framefmt *
> -__v4l2_subdev_state_get_format(struct v4l2_subdev_state *state,
> - unsigned int pad, u32 stream);
> +____v4l2_subdev_state_get_format(struct v4l2_subdev_state *state,
> + unsigned int pad, u32 stream);
>
> /**
> * v4l2_subdev_state_get_crop() - Get pointer to a stream crop rectangle
> @@ -1368,14 +1374,20 @@ __v4l2_subdev_state_get_format(struct v4l2_subdev_state *state,
> * For stream-unaware drivers the crop rectangle for the corresponding pad is
> * returned. If the pad does not exist, NULL is returned.
> */
> -#define v4l2_subdev_state_get_crop(state, pad, ...) \
> - __v4l2_subdev_state_gen_call(crop, ##__VA_ARGS__, , _pad) \
> +#define v4l2_subdev_state_get_crop(state, pad, ...) \
> + __v4l2_subdev_state_gen_call(crop, ##__VA_ARGS__, , _pad) \
> (state, pad, ##__VA_ARGS__)
> -#define __v4l2_subdev_state_get_crop_pad(state, pad) \
> +#define __v4l2_subdev_state_get_crop_pad(state, pad) \
> __v4l2_subdev_state_get_crop(state, pad, 0)
> +#define __v4l2_subdev_state_get_crop(state, pad, stream) \
> + _Generic(state, \
> + const struct v4l2_subdev_state *: ((const struct v4l2_rect *) \
> + ____v4l2_subdev_state_get_crop((struct v4l2_subdev_state *)state, pad, stream)), \
> + default: ____v4l2_subdev_state_get_crop((struct v4l2_subdev_state *)state, pad, stream) \
> + )
> struct v4l2_rect *
> -__v4l2_subdev_state_get_crop(struct v4l2_subdev_state *state, unsigned int pad,
> - u32 stream);
> +____v4l2_subdev_state_get_crop(struct v4l2_subdev_state *state, unsigned int pad,
> + u32 stream);
>
> /**
> * v4l2_subdev_state_get_compose() - Get pointer to a stream compose rectangle
> @@ -1389,14 +1401,20 @@ __v4l2_subdev_state_get_crop(struct v4l2_subdev_state *state, unsigned int pad,
> * For stream-unaware drivers the compose rectangle for the corresponding pad is
> * returned. If the pad does not exist, NULL is returned.
> */
> -#define v4l2_subdev_state_get_compose(state, pad, ...) \
> - __v4l2_subdev_state_gen_call(compose, ##__VA_ARGS__, , _pad) \
> +#define v4l2_subdev_state_get_compose(state, pad, ...) \
> + __v4l2_subdev_state_gen_call(compose, ##__VA_ARGS__, , _pad) \
> (state, pad, ##__VA_ARGS__)
> -#define __v4l2_subdev_state_get_compose_pad(state, pad) \
> +#define __v4l2_subdev_state_get_compose_pad(state, pad) \
> __v4l2_subdev_state_get_compose(state, pad, 0)
> +#define __v4l2_subdev_state_get_compose(state, pad, stream) \
> + _Generic(state, \
> + const struct v4l2_subdev_state *: ((const struct v4l2_rect *) \
> + ____v4l2_subdev_state_get_compose((struct v4l2_subdev_state *)state, pad, stream)), \
> + default: ____v4l2_subdev_state_get_compose((struct v4l2_subdev_state *)state, pad, stream) \
> + )
> struct v4l2_rect *
> -__v4l2_subdev_state_get_compose(struct v4l2_subdev_state *state,
> - unsigned int pad, u32 stream);
> +____v4l2_subdev_state_get_compose(struct v4l2_subdev_state *state,
> + unsigned int pad, u32 stream);
>
> /**
> * v4l2_subdev_state_get_interval() - Get pointer to a stream frame interval
> @@ -1410,14 +1428,20 @@ __v4l2_subdev_state_get_compose(struct v4l2_subdev_state *state,
> * For stream-unaware drivers the frame interval for the corresponding pad is
> * returned. If the pad does not exist, NULL is returned.
> */
> -#define v4l2_subdev_state_get_interval(state, pad, ...) \
> - __v4l2_subdev_state_gen_call(interval, ##__VA_ARGS__, , _pad) \
> +#define v4l2_subdev_state_get_interval(state, pad, ...) \
> + __v4l2_subdev_state_gen_call(interval, ##__VA_ARGS__, , _pad) \
> (state, pad, ##__VA_ARGS__)
> -#define __v4l2_subdev_state_get_interval_pad(state, pad) \
> +#define __v4l2_subdev_state_get_interval_pad(state, pad) \
> __v4l2_subdev_state_get_interval(state, pad, 0)
> +#define __v4l2_subdev_state_get_interval(state, pad, stream) \
> + _Generic(state, \
> + const struct v4l2_subdev_state *: ((const struct v4l2_frac *) \
> + ____v4l2_subdev_state_get_interval((struct v4l2_subdev_state *)state, pad, stream)), \
> + default: ____v4l2_subdev_state_get_interval((struct v4l2_subdev_state *)state, pad, stream) \
Is the cast necessary in the latter case? It would seem like we lose most
of the type safety checks as a result.
Could this be implemented using a similar arrangement than the gen_call
macro above, so that we wouldn't have three very similar sets of macros
here?
> + )
> struct v4l2_fract *
> -__v4l2_subdev_state_get_interval(struct v4l2_subdev_state *state,
> - unsigned int pad, u32 stream);
> +____v4l2_subdev_state_get_interval(struct v4l2_subdev_state *state,
> + unsigned int pad, u32 stream);
>
> #if defined(CONFIG_VIDEO_V4L2_SUBDEV_API)
>
--
Kind regards,
Sakari Ailus
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