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

[Tomi Valkeinen]

On 08/05/2024 21:44, Sakari Ailus wrote:
> 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>

I tested this today on my branches, but apparently forgot to send the 
R-b. So here's mine also:

Reviewed-by: Tomi Valkeinen <tomi.valkeinen at ideasonboard.com>

  Tomi

>> +	_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 *
>