[PATCH v3 1/2] media: v4l2-subdev: Provide const-aware subdev state accessors

[Sakari Ailus]

Hi Laurent,

Thanks for the update.

This is starting to look very nice. A few comments below...

On Tue, May 07, 2024 at 07:19:06PM +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>
> ---
> Changes since v2:
> 
> - Specify types explicitly in _Generic() expression
> - Fix cast of value to const pointer
> 
> Changes since v1:
> 
> - Wrap the accessors with _Generic() using a single macro instead of
>   adding a _Generic() statement in each of them.
> ---
>  include/media/v4l2-subdev.h | 40 +++++++++++++++++++++++++------------
>  1 file changed, 27 insertions(+), 13 deletions(-)
> 
> diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
> index e30c463d90e5..cd3e9e2ebe4d 100644
> --- a/include/media/v4l2-subdev.h
> +++ b/include/media/v4l2-subdev.h
> @@ -1326,6 +1326,16 @@ void v4l2_subdev_cleanup(struct v4l2_subdev *sd);
>  #define __v4l2_subdev_state_gen_call(NAME, _1, ARG, ...)	\
>  	__v4l2_subdev_state_get_ ## NAME ## ARG
>  
> +/*
> + * A macro to constify the return value of the state accessors when the state
> + * parameter is const.
> + */
> +#define __v4l2_subdev_state_constify_call(state, value)				\

This function just changes the return value constness. How about calling it
e.g. __v4l2_subdev_state_constify_ret instead?

Either way,

Reviewed-by: Sakari Ailus <sakari.ailus at linux.intel.com>

> +	_Generic(state,								\
> +		const struct v4l2_subdev_state *: (const typeof(*(value)) *)(value), \
> +		struct v4l2_subdev_state *: (value)				\
> +	)
> +
>  /**
>   * v4l2_subdev_state_get_format() - Get pointer to a stream format
>   * @state: subdevice state
> @@ -1340,16 +1350,17 @@ 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.

These function names are missing _get after the prefix.

Could you also add the interval function here, too?

The would fit well for a separate patch.

>   */
> -#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(state, pad, ...)				\
> +	__v4l2_subdev_state_constify_call(state,				\
> +		__v4l2_subdev_state_gen_call(format, ##__VA_ARGS__, , _pad)	\
> +			((struct v4l2_subdev_state *)state, pad, ##__VA_ARGS__))
>  #define __v4l2_subdev_state_get_format_pad(state, pad)	\
>  	__v4l2_subdev_state_get_format(state, pad, 0)
>  struct v4l2_mbus_framefmt *
> @@ -1368,9 +1379,10 @@ __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)	\
> -		(state, pad, ##__VA_ARGS__)
> +#define v4l2_subdev_state_get_crop(state, pad, ...)				\
> +	__v4l2_subdev_state_constify_call(state,				\
> +		__v4l2_subdev_state_gen_call(crop, ##__VA_ARGS__, , _pad)	\
> +			((struct v4l2_subdev_state *)state, pad, ##__VA_ARGS__))
>  #define __v4l2_subdev_state_get_crop_pad(state, pad)	\
>  	__v4l2_subdev_state_get_crop(state, pad, 0)
>  struct v4l2_rect *
> @@ -1389,9 +1401,10 @@ __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)	\
> -		(state, pad, ##__VA_ARGS__)
> +#define v4l2_subdev_state_get_compose(state, pad, ...)				\
> +	__v4l2_subdev_state_constify_call(state,				\
> +		__v4l2_subdev_state_gen_call(compose, ##__VA_ARGS__, , _pad)	\
> +			((struct v4l2_subdev_state *)state, pad, ##__VA_ARGS__))
>  #define __v4l2_subdev_state_get_compose_pad(state, pad)	\
>  	__v4l2_subdev_state_get_compose(state, pad, 0)
>  struct v4l2_rect *
> @@ -1410,9 +1423,10 @@ __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)	\
> -		(state, pad, ##__VA_ARGS__)
> +#define v4l2_subdev_state_get_interval(state, pad, ...)				\
> +	__v4l2_subdev_state_constify_call(state,				\
> +		__v4l2_subdev_state_gen_call(interval, ##__VA_ARGS__, , _pad)	\
> +			((struct v4l2_subdev_state *)state, pad, ##__VA_ARGS__))
>  #define __v4l2_subdev_state_get_interval_pad(state, pad)	\
>  	__v4l2_subdev_state_get_interval(state, pad, 0)
>  struct v4l2_fract *

-- 
Kind regards,

Sakari Ailus