include/media/v4l2-ctrls.h - pub/scm/linux/kernel/git/ebiederm/linux-namespace-control-devel - Git at Google

 /*
     V4L2 controls support header.

     Copyright (C) 2010  Hans Verkuil <hverkuil@xs4all.nl>

     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation; either version 2 of the License, or
     (at your option) any later version.

     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with this program; if not, write to the Free Software
     Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  */

 #ifndef _V4L2_CTRLS_H
 #define _V4L2_CTRLS_H

 #include <linux/list.h>
 #include <linux/device.h>
 #include <linux/videodev2.h>

 /* forward references */
 struct v4l2_ctrl_handler;
 struct v4l2_ctrl;
 struct video_device;
 struct v4l2_subdev;

 /** struct v4l2_ctrl_ops - The control operations that the driver has to provide.
   * @g_volatile_ctrl: Get a new value for this control. Generally only relevant
   *		for volatile (and usually read-only) controls such as a control
   *		that returns the current signal strength which changes
   *		continuously.
   *		If not set, then the currently cached value will be returned.
   * @try_ctrl:	Test whether the control's value is valid. Only relevant when
   *		the usual min/max/step checks are not sufficient.
   * @s_ctrl:	Actually set the new control value. s_ctrl is compulsory. The
   *		ctrl->handler->lock is held when these ops are called, so no
   *		one else can access controls owned by that handler.
   */
 struct v4l2_ctrl_ops {
 	int (*g_volatile_ctrl)(struct v4l2_ctrl *ctrl);
 	int (*try_ctrl)(struct v4l2_ctrl *ctrl);
 	int (*s_ctrl)(struct v4l2_ctrl *ctrl);
 };

 /** struct v4l2_ctrl - The control structure.
   * @node:	The list node.
   * @handler:	The handler that owns the control.
   * @cluster:	Point to start of cluster array.
   * @ncontrols:	Number of controls in cluster array.
   * @done:	Internal flag: set for each processed control.
   * @is_new:	Set when the user specified a new value for this control. It
   *		is also set when called from v4l2_ctrl_handler_setup. Drivers
   *		should never set this flag.
   * @is_private: If set, then this control is private to its handler and it
   *		will not be added to any other handlers. Drivers can set
   *		this flag.
   * @is_volatile: If set, then this control is volatile. This means that the
   *		control's current value cannot be cached and needs to be
   *		retrieved through the g_volatile_ctrl op. Drivers can set
   *		this flag.
   * @ops:	The control ops.
   * @id:	The control ID.
   * @name:	The control name.
   * @type:	The control type.
   * @minimum:	The control's minimum value.
   * @maximum:	The control's maximum value.
   * @default_value: The control's default value.
   * @step:	The control's step value for non-menu controls.
   * @menu_skip_mask: The control's skip mask for menu controls. This makes it
   *		easy to skip menu items that are not valid. If bit X is set,
   *		then menu item X is skipped. Of course, this only works for
   *		menus with <= 32 menu items. There are no menus that come
   *		close to that number, so this is OK. Should we ever need more,
   *		then this will have to be extended to a u64 or a bit array.
   * @qmenu:	A const char * array for all menu items. Array entries that are
   *		empty strings ("") correspond to non-existing menu items (this
   *		is in addition to the menu_skip_mask above). The last entry
   *		must be NULL.
   * @flags:	The control's flags.
   * @cur:	The control's current value.
   * @val:	The control's new s32 value.
   * @val64:	The control's new s64 value.
   * @string:	The control's new string value.
   * @priv:	The control's private pointer. For use by the driver. It is
   *		untouched by the control framework. Note that this pointer is
   *		not freed when the control is deleted. Should this be needed
   *		then a new internal bitfield can be added to tell the framework
   *		to free this pointer.
   */
 struct v4l2_ctrl {
 	/* Administrative fields */
 	struct list_head node;
 	struct v4l2_ctrl_handler *handler;
 	struct v4l2_ctrl **cluster;
 	unsigned ncontrols;
 	unsigned int done:1;

 	unsigned int is_new:1;
 	unsigned int is_private:1;
 	unsigned int is_volatile:1;

 	const struct v4l2_ctrl_ops *ops;
 	u32 id;
 	const char *name;
 	enum v4l2_ctrl_type type;
 	s32 minimum, maximum, default_value;
 	union {
 		u32 step;
 		u32 menu_skip_mask;
 	};
 	const char * const *qmenu;
 	unsigned long flags;
 	union {
 		s32 val;
 		s64 val64;
 		char *string;
 	} cur;
 	union {
 		s32 val;
 		s64 val64;
 		char *string;
 	};
 	void *priv;
 };

 /** struct v4l2_ctrl_ref - The control reference.
   * @node:	List node for the sorted list.
   * @next:	Single-link list node for the hash.
   * @ctrl:	The actual control information.
   *
   * Each control handler has a list of these refs. The list_head is used to
   * keep a sorted-by-control-ID list of all controls, while the next pointer
   * is used to link the control in the hash's bucket.
   */
 struct v4l2_ctrl_ref {
 	struct list_head node;
 	struct v4l2_ctrl_ref *next;
 	struct v4l2_ctrl *ctrl;
 };

 /** struct v4l2_ctrl_handler - The control handler keeps track of all the
   * controls: both the controls owned by the handler and those inherited
   * from other handlers.
   * @lock:	Lock to control access to this handler and its controls.
   * @ctrls:	The list of controls owned by this handler.
   * @ctrl_refs:	The list of control references.
   * @cached:	The last found control reference. It is common that the same
   *		control is needed multiple times, so this is a simple
   *		optimization.
   * @buckets:	Buckets for the hashing. Allows for quick control lookup.
   * @nr_of_buckets: Total number of buckets in the array.
   * @error:	The error code of the first failed control addition.
   */
 struct v4l2_ctrl_handler {
 	struct mutex lock;
 	struct list_head ctrls;
 	struct list_head ctrl_refs;
 	struct v4l2_ctrl_ref *cached;
 	struct v4l2_ctrl_ref **buckets;
 	u16 nr_of_buckets;
 	int error;
 };

 /** struct v4l2_ctrl_config - Control configuration structure.
   * @ops:	The control ops.
   * @id:	The control ID.
   * @name:	The control name.
   * @type:	The control type.
   * @min:	The control's minimum value.
   * @max:	The control's maximum value.
   * @step:	The control's step value for non-menu controls.
   * @def: 	The control's default value.
   * @flags:	The control's flags.
   * @menu_skip_mask: The control's skip mask for menu controls. This makes it
   *		easy to skip menu items that are not valid. If bit X is set,
   *		then menu item X is skipped. Of course, this only works for
   *		menus with <= 32 menu items. There are no menus that come
   *		close to that number, so this is OK. Should we ever need more,
   *		then this will have to be extended to a u64 or a bit array.
   * @qmenu:	A const char * array for all menu items. Array entries that are
   *		empty strings ("") correspond to non-existing menu items (this
   *		is in addition to the menu_skip_mask above). The last entry
   *		must be NULL.
   * @is_private: If set, then this control is private to its handler and it
   *		will not be added to any other handlers.
   * @is_volatile: If set, then this control is volatile. This means that the
   *		control's current value cannot be cached and needs to be
   *		retrieved through the g_volatile_ctrl op.
   */
 struct v4l2_ctrl_config {
 	const struct v4l2_ctrl_ops *ops;
 	u32 id;
 	const char *name;
 	enum v4l2_ctrl_type type;
 	s32 min;
 	s32 max;
 	u32 step;
 	s32 def;
 	u32 flags;
 	u32 menu_skip_mask;
 	const char * const *qmenu;
 	unsigned int is_private:1;
 	unsigned int is_volatile:1;
 };

 /** v4l2_ctrl_fill() - Fill in the control fields based on the control ID.
   *
   * This works for all standard V4L2 controls.
   * For non-standard controls it will only fill in the given arguments
   * and @name will be NULL.
   *
   * This function will overwrite the contents of @name, @type and @flags.
   * The contents of @min, @max, @step and @def may be modified depending on
   * the type.
   *
   * Do not use in drivers! It is used internally for backwards compatibility
   * control handling only. Once all drivers are converted to use the new
   * control framework this function will no longer be exported.
   */
 void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
 		    s32 *min, s32 *max, s32 *step, s32 *def, u32 *flags);


 /** v4l2_ctrl_handler_init() - Initialize the control handler.
   * @hdl:	The control handler.
   * @nr_of_controls_hint: A hint of how many controls this handler is
   *		expected to refer to. This is the total number, so including
   *		any inherited controls. It doesn't have to be precise, but if
   *		it is way off, then you either waste memory (too many buckets
   *		are allocated) or the control lookup becomes slower (not enough
   *		buckets are allocated, so there are more slow list lookups).
   *		It will always work, though.
   *
   * Returns an error if the buckets could not be allocated. This error will
   * also be stored in @hdl->error.
   */
 int v4l2_ctrl_handler_init(struct v4l2_ctrl_handler *hdl,
 			   unsigned nr_of_controls_hint);

 /** v4l2_ctrl_handler_free() - Free all controls owned by the handler and free
   * the control list.
   * @hdl:	The control handler.
   *
   * Does nothing if @hdl == NULL.
   */
 void v4l2_ctrl_handler_free(struct v4l2_ctrl_handler *hdl);

 /** v4l2_ctrl_handler_setup() - Call the s_ctrl op for all controls belonging
   * to the handler to initialize the hardware to the current control values.
   * @hdl:	The control handler.
   *
   * Button controls will be skipped, as are read-only controls.
   *
   * If @hdl == NULL, then this just returns 0.
   */
 int v4l2_ctrl_handler_setup(struct v4l2_ctrl_handler *hdl);

 /** v4l2_ctrl_handler_log_status() - Log all controls owned by the handler.
   * @hdl:	The control handler.
   * @prefix:	The prefix to use when logging the control values. If the
   *		prefix does not end with a space, then ": " will be added
   *		after the prefix. If @prefix == NULL, then no prefix will be
   *		used.
   *
   * For use with VIDIOC_LOG_STATUS.
   *
   * Does nothing if @hdl == NULL.
   */
 void v4l2_ctrl_handler_log_status(struct v4l2_ctrl_handler *hdl,
 				  const char *prefix);

 /** v4l2_ctrl_new_custom() - Allocate and initialize a new custom V4L2
   * control.
   * @hdl:	The control handler.
   * @cfg:	The control's configuration data.
   * @priv:	The control's driver-specific private data.
   *
   * If the &v4l2_ctrl struct could not be allocated then NULL is returned
   * and @hdl->error is set to the error code (if it wasn't set already).
   */
 struct v4l2_ctrl *v4l2_ctrl_new_custom(struct v4l2_ctrl_handler *hdl,
 			const struct v4l2_ctrl_config *cfg, void *priv);

 /** v4l2_ctrl_new_std() - Allocate and initialize a new standard V4L2 non-menu control.
   * @hdl:	The control handler.
   * @ops:	The control ops.
   * @id:	The control ID.
   * @min:	The control's minimum value.
   * @max:	The control's maximum value.
   * @step:	The control's step value
   * @def: 	The control's default value.
   *
   * If the &v4l2_ctrl struct could not be allocated, or the control
   * ID is not known, then NULL is returned and @hdl->error is set to the
   * appropriate error code (if it wasn't set already).
   *
   * If @id refers to a menu control, then this function will return NULL.
   *
   * Use v4l2_ctrl_new_std_menu() when adding menu controls.
   */
 struct v4l2_ctrl *v4l2_ctrl_new_std(struct v4l2_ctrl_handler *hdl,
 			const struct v4l2_ctrl_ops *ops,
 			u32 id, s32 min, s32 max, u32 step, s32 def);

 /** v4l2_ctrl_new_std_menu() - Allocate and initialize a new standard V4L2 menu control.
   * @hdl:	The control handler.
   * @ops:	The control ops.
   * @id:	The control ID.
   * @max:	The control's maximum value.
   * @mask: 	The control's skip mask for menu controls. This makes it
   *		easy to skip menu items that are not valid. If bit X is set,
   *		then menu item X is skipped. Of course, this only works for
   *		menus with <= 32 menu items. There are no menus that come
   *		close to that number, so this is OK. Should we ever need more,
   *		then this will have to be extended to a u64 or a bit array.
   * @def: 	The control's default value.
   *
   * Same as v4l2_ctrl_new_std(), but @min is set to 0 and the @mask value
   * determines which menu items are to be skipped.
   *
   * If @id refers to a non-menu control, then this function will return NULL.
   */
 struct v4l2_ctrl *v4l2_ctrl_new_std_menu(struct v4l2_ctrl_handler *hdl,
 			const struct v4l2_ctrl_ops *ops,
 			u32 id, s32 max, s32 mask, s32 def);

 /** v4l2_ctrl_add_ctrl() - Add a control from another handler to this handler.
   * @hdl:	The control handler.
   * @ctrl:	The control to add.
   *
   * It will return NULL if it was unable to add the control reference.
   * If the control already belonged to the handler, then it will do
   * nothing and just return @ctrl.
   */
 struct v4l2_ctrl *v4l2_ctrl_add_ctrl(struct v4l2_ctrl_handler *hdl,
 					  struct v4l2_ctrl *ctrl);

 /** v4l2_ctrl_add_handler() - Add all controls from handler @add to
   * handler @hdl.
   * @hdl:	The control handler.
   * @add:	The control handler whose controls you want to add to
   *		the @hdl control handler.
   *
   * Does nothing if either of the two is a NULL pointer.
   * In case of an error @hdl->error will be set to the error code (if it
   * wasn't set already).
   */
 int v4l2_ctrl_add_handler(struct v4l2_ctrl_handler *hdl,
 			  struct v4l2_ctrl_handler *add);


 /** v4l2_ctrl_cluster() - Mark all controls in the cluster as belonging to that cluster.
   * @ncontrols:	The number of controls in this cluster.
   * @controls: 	The cluster control array of size @ncontrols.
   */
 void v4l2_ctrl_cluster(unsigned ncontrols, struct v4l2_ctrl **controls);


 /** v4l2_ctrl_find() - Find a control with the given ID.
   * @hdl:	The control handler.
   * @id:	The control ID to find.
   *
   * If @hdl == NULL this will return NULL as well. Will lock the handler so
   * do not use from inside &v4l2_ctrl_ops.
   */
 struct v4l2_ctrl *v4l2_ctrl_find(struct v4l2_ctrl_handler *hdl, u32 id);

 /** v4l2_ctrl_activate() - Make the control active or inactive.
   * @ctrl:	The control to (de)activate.
   * @active:	True if the control should become active.
   *
   * This sets or clears the V4L2_CTRL_FLAG_INACTIVE flag atomically.
   * Does nothing if @ctrl == NULL.
   * This will usually be called from within the s_ctrl op.
   *
   * This function can be called regardless of whether the control handler
   * is locked or not.
   */
 void v4l2_ctrl_activate(struct v4l2_ctrl *ctrl, bool active);

 /** v4l2_ctrl_grab() - Mark the control as grabbed or not grabbed.
   * @ctrl:	The control to (de)activate.
   * @grabbed:	True if the control should become grabbed.
   *
   * This sets or clears the V4L2_CTRL_FLAG_GRABBED flag atomically.
   * Does nothing if @ctrl == NULL.
   * This will usually be called when starting or stopping streaming in the
   * driver.
   *
   * This function can be called regardless of whether the control handler
   * is locked or not.
   */
 void v4l2_ctrl_grab(struct v4l2_ctrl *ctrl, bool grabbed);

 /** v4l2_ctrl_lock() - Helper function to lock the handler
   * associated with the control.
   * @ctrl:	The control to lock.
   */
 static inline void v4l2_ctrl_lock(struct v4l2_ctrl *ctrl)
 {
 	mutex_lock(&ctrl->handler->lock);
 }

 /** v4l2_ctrl_lock() - Helper function to unlock the handler
   * associated with the control.
   * @ctrl:	The control to unlock.
   */
 static inline void v4l2_ctrl_unlock(struct v4l2_ctrl *ctrl)
 {
 	mutex_unlock(&ctrl->handler->lock);
 }

 /** v4l2_ctrl_g_ctrl() - Helper function to get the control's value from within a driver.
   * @ctrl:	The control.
   *
   * This returns the control's value safely by going through the control
   * framework. This function will lock the control's handler, so it cannot be
   * used from within the &v4l2_ctrl_ops functions.
   *
   * This function is for integer type controls only.
   */
 s32 v4l2_ctrl_g_ctrl(struct v4l2_ctrl *ctrl);

 /** v4l2_ctrl_s_ctrl() - Helper function to set the control's value from within a driver.
   * @ctrl:	The control.
   * @val:	The new value.
   *
   * This set the control's new value safely by going through the control
   * framework. This function will lock the control's handler, so it cannot be
   * used from within the &v4l2_ctrl_ops functions.
   *
   * This function is for integer type controls only.
   */
 int v4l2_ctrl_s_ctrl(struct v4l2_ctrl *ctrl, s32 val);


 /* Helpers for ioctl_ops. If hdl == NULL then they will all return -EINVAL. */
 int v4l2_queryctrl(struct v4l2_ctrl_handler *hdl, struct v4l2_queryctrl *qc);
 int v4l2_querymenu(struct v4l2_ctrl_handler *hdl, struct v4l2_querymenu *qm);
 int v4l2_g_ctrl(struct v4l2_ctrl_handler *hdl, struct v4l2_control *ctrl);
 int v4l2_s_ctrl(struct v4l2_ctrl_handler *hdl, struct v4l2_control *ctrl);
 int v4l2_g_ext_ctrls(struct v4l2_ctrl_handler *hdl, struct v4l2_ext_controls *c);
 int v4l2_try_ext_ctrls(struct v4l2_ctrl_handler *hdl, struct v4l2_ext_controls *c);
 int v4l2_s_ext_ctrls(struct v4l2_ctrl_handler *hdl, struct v4l2_ext_controls *c);

 /* Helpers for subdevices. If the associated ctrl_handler == NULL then they
    will all return -EINVAL. */
 int v4l2_subdev_queryctrl(struct v4l2_subdev *sd, struct v4l2_queryctrl *qc);
 int v4l2_subdev_querymenu(struct v4l2_subdev *sd, struct v4l2_querymenu *qm);
 int v4l2_subdev_g_ext_ctrls(struct v4l2_subdev *sd, struct v4l2_ext_controls *cs);
 int v4l2_subdev_try_ext_ctrls(struct v4l2_subdev *sd, struct v4l2_ext_controls *cs);
 int v4l2_subdev_s_ext_ctrls(struct v4l2_subdev *sd, struct v4l2_ext_controls *cs);
 int v4l2_subdev_g_ctrl(struct v4l2_subdev *sd, struct v4l2_control *ctrl);
 int v4l2_subdev_s_ctrl(struct v4l2_subdev *sd, struct v4l2_control *ctrl);

 #endif
	/*
	V4L2 controls support header.

	Copyright (C) 2010 Hans Verkuil <hverkuil@xs4all.nl>

	This program is free software; you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation; either version 2 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with this program; if not, write to the Free Software
	Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
	*/

	#ifndef _V4L2_CTRLS_H
	#define _V4L2_CTRLS_H

	#include <linux/list.h>
	#include <linux/device.h>
	#include <linux/videodev2.h>

	/* forward references */
	struct v4l2_ctrl_handler;
	struct v4l2_ctrl;
	struct video_device;
	struct v4l2_subdev;

	/** struct v4l2_ctrl_ops - The control operations that the driver has to provide.
	* @g_volatile_ctrl: Get a new value for this control. Generally only relevant
	* for volatile (and usually read-only) controls such as a control
	* that returns the current signal strength which changes
	* continuously.
	* If not set, then the currently cached value will be returned.
	* @try_ctrl: Test whether the control's value is valid. Only relevant when
	* the usual min/max/step checks are not sufficient.
	* @s_ctrl: Actually set the new control value. s_ctrl is compulsory. The
	* ctrl->handler->lock is held when these ops are called, so no
	* one else can access controls owned by that handler.
	*/
	struct v4l2_ctrl_ops {
	int (g_volatile_ctrl)(struct v4l2_ctrl ctrl);
	int (try_ctrl)(struct v4l2_ctrl ctrl);
	int (s_ctrl)(struct v4l2_ctrl ctrl);
	};

	/** struct v4l2_ctrl - The control structure.
	* @node: The list node.
	* @handler: The handler that owns the control.
	* @cluster: Point to start of cluster array.
	* @ncontrols: Number of controls in cluster array.
	* @done: Internal flag: set for each processed control.
	* @is_new: Set when the user specified a new value for this control. It
	* is also set when called from v4l2_ctrl_handler_setup. Drivers
	* should never set this flag.
	* @is_private: If set, then this control is private to its handler and it
	* will not be added to any other handlers. Drivers can set
	* this flag.
	* @is_volatile: If set, then this control is volatile. This means that the
	* control's current value cannot be cached and needs to be
	* retrieved through the g_volatile_ctrl op. Drivers can set
	* this flag.
	* @ops: The control ops.
	* @id: The control ID.
	* @name: The control name.
	* @type: The control type.
	* @minimum: The control's minimum value.
	* @maximum: The control's maximum value.
	* @default_value: The control's default value.
	* @step: The control's step value for non-menu controls.
	* @menu_skip_mask: The control's skip mask for menu controls. This makes it
	* easy to skip menu items that are not valid. If bit X is set,
	* then menu item X is skipped. Of course, this only works for
	* menus with <= 32 menu items. There are no menus that come
	* close to that number, so this is OK. Should we ever need more,
	* then this will have to be extended to a u64 or a bit array.
	* @qmenu: A const char * array for all menu items. Array entries that are
	* empty strings ("") correspond to non-existing menu items (this
	* is in addition to the menu_skip_mask above). The last entry
	* must be NULL.
	* @flags: The control's flags.
	* @cur: The control's current value.
	* @val: The control's new s32 value.
	* @val64: The control's new s64 value.
	* @string: The control's new string value.
	* @priv: The control's private pointer. For use by the driver. It is
	* untouched by the control framework. Note that this pointer is
	* not freed when the control is deleted. Should this be needed
	* then a new internal bitfield can be added to tell the framework
	* to free this pointer.
	*/
	struct v4l2_ctrl {
	/* Administrative fields */
	struct list_head node;
	struct v4l2_ctrl_handler *handler;
	struct v4l2_ctrl **cluster;
	unsigned ncontrols;
	unsigned int done:1;

	unsigned int is_new:1;
	unsigned int is_private:1;
	unsigned int is_volatile:1;

	const struct v4l2_ctrl_ops *ops;
	u32 id;
	const char *name;
	enum v4l2_ctrl_type type;
	s32 minimum, maximum, default_value;
	union {
	u32 step;
	u32 menu_skip_mask;
	};
	const char * const *qmenu;
	unsigned long flags;
	union {
	s32 val;
	s64 val64;
	char *string;
	} cur;
	union {
	s32 val;
	s64 val64;
	char *string;
	};
	void *priv;
	};

	/** struct v4l2_ctrl_ref - The control reference.
	* @node: List node for the sorted list.
	* @next: Single-link list node for the hash.
	* @ctrl: The actual control information.
	*
	* Each control handler has a list of these refs. The list_head is used to
	* keep a sorted-by-control-ID list of all controls, while the next pointer
	* is used to link the control in the hash's bucket.
	*/
	struct v4l2_ctrl_ref {
	struct list_head node;
	struct v4l2_ctrl_ref *next;
	struct v4l2_ctrl *ctrl;
	};

	/** struct v4l2_ctrl_handler - The control handler keeps track of all the
	* controls: both the controls owned by the handler and those inherited
	* from other handlers.
	* @lock: Lock to control access to this handler and its controls.
	* @ctrls: The list of controls owned by this handler.
	* @ctrl_refs: The list of control references.
	* @cached: The last found control reference. It is common that the same
	* control is needed multiple times, so this is a simple
	* optimization.
	* @buckets: Buckets for the hashing. Allows for quick control lookup.
	* @nr_of_buckets: Total number of buckets in the array.
	* @error: The error code of the first failed control addition.
	*/
	struct v4l2_ctrl_handler {
	struct mutex lock;
	struct list_head ctrls;
	struct list_head ctrl_refs;
	struct v4l2_ctrl_ref *cached;
	struct v4l2_ctrl_ref **buckets;
	u16 nr_of_buckets;
	int error;
	};

	/** struct v4l2_ctrl_config - Control configuration structure.
	* @ops: The control ops.
	* @id: The control ID.
	* @name: The control name.
	* @type: The control type.
	* @min: The control's minimum value.
	* @max: The control's maximum value.
	* @step: The control's step value for non-menu controls.
	* @def: The control's default value.
	* @flags: The control's flags.
	* @menu_skip_mask: The control's skip mask for menu controls. This makes it
	* easy to skip menu items that are not valid. If bit X is set,
	* then menu item X is skipped. Of course, this only works for
	* menus with <= 32 menu items. There are no menus that come
	* close to that number, so this is OK. Should we ever need more,
	* then this will have to be extended to a u64 or a bit array.
	* @qmenu: A const char * array for all menu items. Array entries that are
	* empty strings ("") correspond to non-existing menu items (this
	* is in addition to the menu_skip_mask above). The last entry
	* must be NULL.
	* @is_private: If set, then this control is private to its handler and it
	* will not be added to any other handlers.
	* @is_volatile: If set, then this control is volatile. This means that the
	* control's current value cannot be cached and needs to be
	* retrieved through the g_volatile_ctrl op.
	*/
	struct v4l2_ctrl_config {
	const struct v4l2_ctrl_ops *ops;
	u32 id;
	const char *name;
	enum v4l2_ctrl_type type;
	s32 min;
	s32 max;
	u32 step;
	s32 def;
	u32 flags;
	u32 menu_skip_mask;
	const char * const *qmenu;
	unsigned int is_private:1;
	unsigned int is_volatile:1;
	};

	/** v4l2_ctrl_fill() - Fill in the control fields based on the control ID.
	*
	* This works for all standard V4L2 controls.
	* For non-standard controls it will only fill in the given arguments
	* and @name will be NULL.
	*
	* This function will overwrite the contents of @name, @type and @flags.
	* The contents of @min, @max, @step and @def may be modified depending on
	* the type.
	*
	* Do not use in drivers! It is used internally for backwards compatibility
	* control handling only. Once all drivers are converted to use the new
	* control framework this function will no longer be exported.
	*/
	void v4l2_ctrl_fill(u32 id, const char *name, enum v4l2_ctrl_type type,
	s32 min, s32 max, s32 step, s32 def, u32 *flags);


	/** v4l2_ctrl_handler_init() - Initialize the control handler.
	* @hdl: The control handler.
	* @nr_of_controls_hint: A hint of how many controls this handler is
	* expected to refer to. This is the total number, so including
	* any inherited controls. It doesn't have to be precise, but if
	* it is way off, then you either waste memory (too many buckets
	* are allocated) or the control lookup becomes slower (not enough
	* buckets are allocated, so there are more slow list lookups).
	* It will always work, though.
	*
	* Returns an error if the buckets could not be allocated. This error will
	* also be stored in @hdl->error.
	*/
	int v4l2_ctrl_handler_init(struct v4l2_ctrl_handler *hdl,
	unsigned nr_of_controls_hint);

	/** v4l2_ctrl_handler_free() - Free all controls owned by the handler and free
	* the control list.
	* @hdl: The control handler.
	*
	* Does nothing if @hdl == NULL.
	*/
	void v4l2_ctrl_handler_free(struct v4l2_ctrl_handler *hdl);

	/** v4l2_ctrl_handler_setup() - Call the s_ctrl op for all controls belonging
	* to the handler to initialize the hardware to the current control values.
	* @hdl: The control handler.
	*
	* Button controls will be skipped, as are read-only controls.
	*
	* If @hdl == NULL, then this just returns 0.
	*/
	int v4l2_ctrl_handler_setup(struct v4l2_ctrl_handler *hdl);

	/** v4l2_ctrl_handler_log_status() - Log all controls owned by the handler.
	* @hdl: The control handler.
	* @prefix: The prefix to use when logging the control values. If the
	* prefix does not end with a space, then ": " will be added
	* after the prefix. If @prefix == NULL, then no prefix will be
	* used.
	*
	* For use with VIDIOC_LOG_STATUS.
	*
	* Does nothing if @hdl == NULL.
	*/
	void v4l2_ctrl_handler_log_status(struct v4l2_ctrl_handler *hdl,
	const char *prefix);

	/** v4l2_ctrl_new_custom() - Allocate and initialize a new custom V4L2
	* control.
	* @hdl: The control handler.
	* @cfg: The control's configuration data.
	* @priv: The control's driver-specific private data.
	*
	* If the &v4l2_ctrl struct could not be allocated then NULL is returned
	* and @hdl->error is set to the error code (if it wasn't set already).
	*/
	struct v4l2_ctrl v4l2_ctrl_new_custom(struct v4l2_ctrl_handler hdl,
	const struct v4l2_ctrl_config cfg, void priv);

	/** v4l2_ctrl_new_std() - Allocate and initialize a new standard V4L2 non-menu control.
	* @hdl: The control handler.
	* @ops: The control ops.
	* @id: The control ID.
	* @min: The control's minimum value.
	* @max: The control's maximum value.
	* @step: The control's step value
	* @def: The control's default value.
	*
	* If the &v4l2_ctrl struct could not be allocated, or the control
	* ID is not known, then NULL is returned and @hdl->error is set to the
	* appropriate error code (if it wasn't set already).
	*
	* If @id refers to a menu control, then this function will return NULL.
	*
	* Use v4l2_ctrl_new_std_menu() when adding menu controls.
	*/
	struct v4l2_ctrl v4l2_ctrl_new_std(struct v4l2_ctrl_handler hdl,
	const struct v4l2_ctrl_ops *ops,
	u32 id, s32 min, s32 max, u32 step, s32 def);

	/** v4l2_ctrl_new_std_menu() - Allocate and initialize a new standard V4L2 menu control.
	* @hdl: The control handler.
	* @ops: The control ops.
	* @id: The control ID.
	* @max: The control's maximum value.
	* @mask: The control's skip mask for menu controls. This makes it
	* easy to skip menu items that are not valid. If bit X is set,
	* then menu item X is skipped. Of course, this only works for
	* menus with <= 32 menu items. There are no menus that come
	* close to that number, so this is OK. Should we ever need more,
	* then this will have to be extended to a u64 or a bit array.
	* @def: The control's default value.
	*
	* Same as v4l2_ctrl_new_std(), but @min is set to 0 and the @mask value
	* determines which menu items are to be skipped.
	*
	* If @id refers to a non-menu control, then this function will return NULL.
	*/
	struct v4l2_ctrl v4l2_ctrl_new_std_menu(struct v4l2_ctrl_handler hdl,
	const struct v4l2_ctrl_ops *ops,
	u32 id, s32 max, s32 mask, s32 def);

	/** v4l2_ctrl_add_ctrl() - Add a control from another handler to this handler.
	* @hdl: The control handler.
	* @ctrl: The control to add.
	*
	* It will return NULL if it was unable to add the control reference.
	* If the control already belonged to the handler, then it will do
	* nothing and just return @ctrl.
	*/
	struct v4l2_ctrl v4l2_ctrl_add_ctrl(struct v4l2_ctrl_handler hdl,
	struct v4l2_ctrl *ctrl);

	/** v4l2_ctrl_add_handler() - Add all controls from handler @add to
	* handler @hdl.
	* @hdl: The control handler.
	* @add: The control handler whose controls you want to add to
	* the @hdl control handler.
	*
	* Does nothing if either of the two is a NULL pointer.
	* In case of an error @hdl->error will be set to the error code (if it
	* wasn't set already).
	*/
	int v4l2_ctrl_add_handler(struct v4l2_ctrl_handler *hdl,
	struct v4l2_ctrl_handler *add);


	/** v4l2_ctrl_cluster() - Mark all controls in the cluster as belonging to that cluster.
	* @ncontrols: The number of controls in this cluster.
	* @controls: The cluster control array of size @ncontrols.
	*/
	void v4l2_ctrl_cluster(unsigned ncontrols, struct v4l2_ctrl **controls);


	/** v4l2_ctrl_find() - Find a control with the given ID.
	* @hdl: The control handler.
	* @id: The control ID to find.
	*
	* If @hdl == NULL this will return NULL as well. Will lock the handler so
	* do not use from inside &v4l2_ctrl_ops.
	*/
	struct v4l2_ctrl v4l2_ctrl_find(struct v4l2_ctrl_handler hdl, u32 id);

	/** v4l2_ctrl_activate() - Make the control active or inactive.
	* @ctrl: The control to (de)activate.
	* @active: True if the control should become active.
	*
	* This sets or clears the V4L2_CTRL_FLAG_INACTIVE flag atomically.
	* Does nothing if @ctrl == NULL.
	* This will usually be called from within the s_ctrl op.
	*
	* This function can be called regardless of whether the control handler
	* is locked or not.
	*/
	void v4l2_ctrl_activate(struct v4l2_ctrl *ctrl, bool active);

	/** v4l2_ctrl_grab() - Mark the control as grabbed or not grabbed.
	* @ctrl: The control to (de)activate.
	* @grabbed: True if the control should become grabbed.
	*
	* This sets or clears the V4L2_CTRL_FLAG_GRABBED flag atomically.
	* Does nothing if @ctrl == NULL.
	* This will usually be called when starting or stopping streaming in the
	* driver.
	*
	* This function can be called regardless of whether the control handler
	* is locked or not.
	*/
	void v4l2_ctrl_grab(struct v4l2_ctrl *ctrl, bool grabbed);

	/** v4l2_ctrl_lock() - Helper function to lock the handler
	* associated with the control.
	* @ctrl: The control to lock.
	*/
	static inline void v4l2_ctrl_lock(struct v4l2_ctrl *ctrl)
	{
	mutex_lock(&ctrl->handler->lock);
	}

	/** v4l2_ctrl_lock() - Helper function to unlock the handler
	* associated with the control.
	* @ctrl: The control to unlock.
	*/
	static inline void v4l2_ctrl_unlock(struct v4l2_ctrl *ctrl)
	{
	mutex_unlock(&ctrl->handler->lock);
	}

	/** v4l2_ctrl_g_ctrl() - Helper function to get the control's value from within a driver.
	* @ctrl: The control.
	*
	* This returns the control's value safely by going through the control
	* framework. This function will lock the control's handler, so it cannot be
	* used from within the &v4l2_ctrl_ops functions.
	*
	* This function is for integer type controls only.
	*/
	s32 v4l2_ctrl_g_ctrl(struct v4l2_ctrl *ctrl);

	/** v4l2_ctrl_s_ctrl() - Helper function to set the control's value from within a driver.
	* @ctrl: The control.
	* @val: The new value.
	*
	* This set the control's new value safely by going through the control
	* framework. This function will lock the control's handler, so it cannot be
	* used from within the &v4l2_ctrl_ops functions.
	*
	* This function is for integer type controls only.
	*/
	int v4l2_ctrl_s_ctrl(struct v4l2_ctrl *ctrl, s32 val);


	/* Helpers for ioctl_ops. If hdl == NULL then they will all return -EINVAL. */
	int v4l2_queryctrl(struct v4l2_ctrl_handler hdl, struct v4l2_queryctrl qc);
	int v4l2_querymenu(struct v4l2_ctrl_handler hdl, struct v4l2_querymenu qm);
	int v4l2_g_ctrl(struct v4l2_ctrl_handler hdl, struct v4l2_control ctrl);
	int v4l2_s_ctrl(struct v4l2_ctrl_handler hdl, struct v4l2_control ctrl);
	int v4l2_g_ext_ctrls(struct v4l2_ctrl_handler hdl, struct v4l2_ext_controls c);
	int v4l2_try_ext_ctrls(struct v4l2_ctrl_handler hdl, struct v4l2_ext_controls c);
	int v4l2_s_ext_ctrls(struct v4l2_ctrl_handler hdl, struct v4l2_ext_controls c);

	/* Helpers for subdevices. If the associated ctrl_handler == NULL then they
	will all return -EINVAL. */
	int v4l2_subdev_queryctrl(struct v4l2_subdev sd, struct v4l2_queryctrl qc);
	int v4l2_subdev_querymenu(struct v4l2_subdev sd, struct v4l2_querymenu qm);
	int v4l2_subdev_g_ext_ctrls(struct v4l2_subdev sd, struct v4l2_ext_controls cs);
	int v4l2_subdev_try_ext_ctrls(struct v4l2_subdev sd, struct v4l2_ext_controls cs);
	int v4l2_subdev_s_ext_ctrls(struct v4l2_subdev sd, struct v4l2_ext_controls cs);
	int v4l2_subdev_g_ctrl(struct v4l2_subdev sd, struct v4l2_control ctrl);
	int v4l2_subdev_s_ctrl(struct v4l2_subdev sd, struct v4l2_control ctrl);

	#endif