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[media] v4l2-controls.txt: update to the new way of accessing controls 

The way current and new values are accessed has changed. Update the
document to bring it up to date with the code.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Reviewed-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
This commit is contained in:
Hans Verkuil 2014-01-20 07:21:31 -03:00 committed by Mauro Carvalho Chehab
parent 680a513968
commit 04d8b04e50
1 changed files with 38 additions and 23 deletions
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61
Documentation/video4linux/v4l2-controls.txt
View File

@ -77,9 +77,9 @@ Basic usage for V4L2 and sub-device drivers
Where foo->v4l2_dev is of type struct v4l2_device.
Finally, remove all control functions from your v4l2_ioctl_ops:
vidioc_queryctrl, vidioc_querymenu, vidioc_g_ctrl, vidioc_s_ctrl,
vidioc_g_ext_ctrls, vidioc_try_ext_ctrls and vidioc_s_ext_ctrls.
Finally, remove all control functions from your v4l2_ioctl_ops (if any):
vidioc_queryctrl, vidioc_query_ext_ctrl, vidioc_querymenu, vidioc_g_ctrl,
vidioc_s_ctrl, vidioc_g_ext_ctrls, vidioc_try_ext_ctrls and vidioc_s_ext_ctrls.
Those are now no longer needed.
1.3.2) For sub-device drivers do this:
@ -258,8 +258,8 @@ The new control value has already been validated, so all you need to do is
to actually update the hardware registers.
You're done! And this is sufficient for most of the drivers we have. No need
to do any validation of control values, or implement QUERYCTRL/QUERYMENU. And
G/S_CTRL as well as G/TRY/S_EXT_CTRLS are automatically supported.
to do any validation of control values, or implement QUERYCTRL, QUERY_EXT_CTRL
and QUERYMENU. And G/S_CTRL as well as G/TRY/S_EXT_CTRLS are automatically supported.
==============================================================================
@ -288,30 +288,45 @@ of v4l2_device.
Accessing Control Values
========================
The v4l2_ctrl struct contains these two unions:
The following union is used inside the control framework to access control
values:
/* The current control value. */
union {
union v4l2_ctrl_ptr {
s32 *p_s32;
s64 *p_s64;
char *p_char;
void *p;
};
The v4l2_ctrl struct contains these fields that can be used to access both
current and new values:
s32 val;
struct {
s32 val;
s64 val64;
char *string;
} cur;
/* The new control value. */
union {
s32 val;
s64 val64;
char *string;
};
Within the control ops you can freely use these. The val and val64 speak for
themselves. The string pointers point to character buffers of length
union v4l2_ctrl_ptr p_new;
union v4l2_ctrl_ptr p_cur;
If the control has a simple s32 type type, then:
&ctrl->val == ctrl->p_new.p_s32
&ctrl->cur.val == ctrl->p_cur.p_s32
For all other types use ctrl->p_cur.p<something>. Basically the val
and cur.val fields can be considered an alias since these are used so often.
Within the control ops you can freely use these. The val and cur.val speak for
themselves. The p_char pointers point to character buffers of length
ctrl->maximum + 1, and are always 0-terminated.
In most cases 'cur' contains the current cached control value. When you create
a new control this value is made identical to the default value. After calling
v4l2_ctrl_handler_setup() this value is passed to the hardware. It is generally
a good idea to call this function.
Unless the control is marked volatile the p_cur field points to the the
current cached control value. When you create a new control this value is made
identical to the default value. After calling v4l2_ctrl_handler_setup() this
value is passed to the hardware. It is generally a good idea to call this
function.
Whenever a new value is set that new value is automatically cached. This means
that most drivers do not need to implement the g_volatile_ctrl() op. The
@ -363,7 +378,7 @@ You can also take the handler lock yourself:
mutex_lock(&state->ctrl_handler.lock);
pr_info("String value is '%s'\n", ctrl1->p_cur.p_char);
printk(KERN_INFO "Integer value is '%s'\n", ctrl2->cur.val);
pr_info("Integer value is '%s'\n", ctrl2->cur.val);
mutex_unlock(&state->ctrl_handler.lock);