linux-kernel - Re: [PATCH RFC v2 4/6] media: v4l2-ctrls: add lens group speed controls for zoom and focus

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Message-ID: <64902ea4-e934-2813-2dd2-cb568e1f8030@wolfvision.net>
Date:   Tue, 13 Jun 2023 09:49:40 +0200
From:   Michael Riesch <michael.riesch@...fvision.net>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        libcamera-devel@...ts.libcamera.org,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Matthias Fend <Matthias.Fend@...fvision.net>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v2 4/6] media: v4l2-ctrls: add lens group speed
 controls for zoom and focus

Hi Laurent,

On 6/7/23 09:07, Laurent Pinchart wrote:
> Hi Michael,
> 
> Thank you for the patch.
> 
> On Tue, Apr 25, 2023 at 11:45:14AM +0200, Michael Riesch wrote:
>> Add the controls V4L2_CID_FOCUS_SPEED and V4L2_CID_ZOOM_SPEED that set
>> the speed of the zoom lens group and focus lens group, respectively.
> 
> Ah, now the UVC relative focus and zoom controls could be implemented
> ;-) They still don't match the definition of the corresponding V4L2
> controls, so I'm still tempted to deprecate both.

There is also V4L2_CID_ZOOM_CONTINUOUS that could be mapped to the UVC
relative zoom, if I am not mistaken. I had a similar
V4L2_CID_FOCUS_CONTINUOUS control in mind briefly, but for our use case
this would not be general enough.

>> Signed-off-by: Michael Riesch <michael.riesch@...fvision.net>
>> ---
>>  Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst | 10 ++++++++++
>>  drivers/media/v4l2-core/v4l2-ctrls-defs.c                  |  2 ++
>>  include/uapi/linux/v4l2-controls.h                         |  2 ++
>>  3 files changed, 14 insertions(+)
>>
>> diff --git a/Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst b/Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst
>> index 3ea4175f9619..a17620ab03b9 100644
>> --- a/Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst
>> +++ b/Documentation/userspace-api/media/v4l/ext-ctrls-camera.rst
>> @@ -174,6 +174,11 @@ enum v4l2_exposure_metering -
>>  	will not transition from this state until another action is performed
>>  	by an application.
>>  
>> +``V4L2_CID_FOCUS_SPEED (integer)``
>> +    Set the speed with which the focus lens group of the camera is moved
>> +    (V4L2_CID_FOCUS_ABSOLUTE and V4L2_CID_FOCUS_RELATIVE). The unit is
>> +    driver-specific. The value should be a positive integer.
>> +
> 
> Could you explain your expected use cases for focus and zoom speed ?

As I outlined in the cover letter, the speed of the lenses can be
adjusted. This can be used e.g., in the autofocus algorithm, where a
coarse scan and a fine grained scan can be implemented using different
speeds.

The adjustable zoom speed control is simply there to give the user the
choice to zoom in/out fast or slow.

Should this go into the documentation?

Best regards,
Michael

> 
>>  ``V4L2_CID_FOCUS_AUTO (boolean)``
>>      Enables continuous automatic focus adjustments. The effect of manual
>>      focus adjustments while this feature is enabled is undefined,
>> @@ -287,6 +292,11 @@ enum v4l2_auto_focus_range -
>>  	not transition from this state until another action is performed by an
>>  	application.
>>  
>> +``V4L2_CID_ZOOM_SPEED (integer)``
>> +    Set the speed with which the zoom lens group of the camera is moved
>> +    (V4L2_CID_ZOOM_ABSOLUTE and V4L2_CID_ZOOM_RELATIVE). The unit is
>> +    driver-specific. The value should be a positive integer.
>> +
>>  ``V4L2_CID_IRIS_ABSOLUTE (integer)``
>>      This control sets the camera's aperture to the specified value. The
>>      unit is undefined. Larger values open the iris wider, smaller values
>> diff --git a/drivers/media/v4l2-core/v4l2-ctrls-defs.c b/drivers/media/v4l2-core/v4l2-ctrls-defs.c
>> index 794ef3ab0c02..3ef465ba73bd 100644
>> --- a/drivers/media/v4l2-core/v4l2-ctrls-defs.c
>> +++ b/drivers/media/v4l2-core/v4l2-ctrls-defs.c
>> @@ -1048,6 +1048,8 @@ const char *v4l2_ctrl_get_name(u32 id)
>>  	case V4L2_CID_FOCUS_STATUS:		return "Focus, Status";
>>  	case V4L2_CID_ZOOM_CURRENT:		return "Zoom, Current";
>>  	case V4L2_CID_ZOOM_STATUS:		return "Zoom, Status";
>> +	case V4L2_CID_FOCUS_SPEED:		return "Focus, Speed";
>> +	case V4L2_CID_ZOOM_SPEED:		return "Zoom, Speed";
>>  
>>  	/* FM Radio Modulator controls */
>>  	/* Keep the order of the 'case's the same as in v4l2-controls.h! */
>> diff --git a/include/uapi/linux/v4l2-controls.h b/include/uapi/linux/v4l2-controls.h
>> index 793ee8c65e87..8d84508d4db8 100644
>> --- a/include/uapi/linux/v4l2-controls.h
>> +++ b/include/uapi/linux/v4l2-controls.h
>> @@ -1001,6 +1001,8 @@ enum v4l2_auto_focus_range {
>>  #define V4L2_CID_FOCUS_STATUS			(V4L2_CID_CAMERA_CLASS_BASE+38)
>>  #define V4L2_CID_ZOOM_CURRENT			(V4L2_CID_CAMERA_CLASS_BASE+39)
>>  #define V4L2_CID_ZOOM_STATUS			(V4L2_CID_CAMERA_CLASS_BASE+40)
>> +#define V4L2_CID_FOCUS_SPEED			(V4L2_CID_CAMERA_CLASS_BASE+41)
>> +#define V4L2_CID_ZOOM_SPEED			(V4L2_CID_CAMERA_CLASS_BASE+42)
>>  
>>  /* FM Modulator class control IDs */
>>  
>