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Subject: media: v4l2-subdev: Provide const-aware subdev state accessors
Author: Laurent Pinchart <laurent.pinchart+rene...@ideasonboard.com>
Date: Thu May 9 00:40:43 2024 +0300
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+rene...@ideasonboard.com>
Reviewed-by: Sakari Ailus <sakari.ai...@linux.intel.com>
Reviewed-by: Tomi Valkeinen <tomi.valkei...@ideasonboard.com>
[Sakari Ailus: Drop the word "below" from the text.]
Signed-off-by: Sakari Ailus <sakari.ai...@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-ci...@xs4all.nl>
include/media/v4l2-subdev.h | 54 ++++++++++++++++++++++++++++++---------------
1 file changed, 36 insertions(+), 18 deletions(-)
---
diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
index ed339f0116bf..1b74e037e440 100644
--- a/include/media/v4l2-subdev.h
+++ b/include/media/v4l2-subdev.h
@@ -1337,6 +1337,16 @@ 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_ret(state, value)
\
+ _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
@@ -1352,15 +1362,20 @@ 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_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(),
v4l2_subdev_state_compose()
- * and v4l2_subdev_state_get_interval() below.
- */
-#define v4l2_subdev_state_get_format(state, pad, ...) \
- __v4l2_subdev_state_gen_call(format, ##__VA_ARGS__, , _pad) \
- (state, pad, ##__VA_ARGS__)
+ * macro 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. The
+ * __v4l2_subdev_state_constify_ret() macro constifies the returned pointer
+ * when the state is const, allowing the state accessors to guarantee
+ * const-correctness in all cases.
+ *
+ * A similar arrangement is used for v4l2_subdev_state_crop(),
+ * v4l2_subdev_state_compose() and v4l2_subdev_state_get_interval() below.
+ */
+#define v4l2_subdev_state_get_format(state, pad, ...)
\
+ __v4l2_subdev_state_constify_ret(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 *
@@ -1379,9 +1394,10 @@ __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_ret(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 *
@@ -1400,9 +1416,10 @@ __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_ret(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 *
@@ -1421,9 +1438,10 @@ __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_ret(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 *
