Re: [PATCH v3 1/2] v4l: Add camera voice coil lens control class, current control

[Mauro Carvalho Chehab <mchehab@s-opensource.com>]

Hi Sakari,

Em Tue, 14 Feb 2017 14:20:22 +0200
Sakari Ailus <sakari.ailus@linux.intel.com> escreveu:

> Add a V4L2 control class for voice coil lens driver devices. These are
> simple devices that are used to move a camera lens from its resting
> position.

>From some past threads with this patch, you mentioned that:

"The FOCUS_ABSOLUTE control really is not a best control ID to
 control a voice coil driver's current."

However, I'm not seeing any explanation there at the thread, at
the patch description or at the documentation explaining why, and,
more important, when someone should use the focus control or the
camera voice coil control.

Worse than that, patch 2/2 gives the false sensation that both
controls are equal.

Ok, I understand that they need to be identical on the existing
driver, in order to keep backward compatibility, but I'm afraid
that, without a clear distinction between them at the documentation,
people may just clone the existing code on other drivers.

So, please add more details to patch 1/2.

Regards,
Mauro

> 
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
>  Documentation/media/uapi/v4l/extended-controls.rst | 28 ++++++++++++++++++++++
>  include/uapi/linux/v4l2-controls.h                 |  8 +++++++
>  2 files changed, 36 insertions(+)
> 
> diff --git a/Documentation/media/uapi/v4l/extended-controls.rst b/Documentation/media/uapi/v4l/extended-controls.rst
> index abb1057..a75451a 100644
> --- a/Documentation/media/uapi/v4l/extended-controls.rst
> +++ b/Documentation/media/uapi/v4l/extended-controls.rst
> @@ -3022,6 +3022,34 @@ Image Process Control IDs
>      driver specific and are documented in :ref:`v4l-drivers`.
>  
>  
> +.. _voice-coil-lens-controls:
> +
> +Voice Coil Lens Control Reference
> +=================================
> +
> +The Voice Coil class controls are used to control voice coil lens
> +devices. These are very simple devices that consist of a voice coil, a
> +spring and a lens. The current applied on the voice coil is used to
> +move the lens away from the resting position which typically is (close
> +to) infinity. The higher the current applied, the closer the lens is
> +typically focused.
> +
> +.. _voice-coil-lens-control-is:
> +
> +Voice Coil Lens Control IDs
> +---------------------------
> +
> +``V4L2_CID_VOICE_COIL_CLASS (class)``
> +    The VOICE_COIL class descriptor.
> +
> +``V4L2_CID_VOICE_COIL_CURRENT (integer)``
> +    Current applied on a voice coil. The more current is applied, the
> +    more is the position of the lens moved from its resting position.
> +    Do note that there may be a ringing effect; the lens will
> +    oscillate after changing the current applied unless the device
> +    implements ringing compensation.
> +
> +
>  .. _dv-controls:
>  
>  Digital Video Control Reference
> diff --git a/include/uapi/linux/v4l2-controls.h b/include/uapi/linux/v4l2-controls.h
> index 0d2e1e0..9ef152b 100644
> --- a/include/uapi/linux/v4l2-controls.h
> +++ b/include/uapi/linux/v4l2-controls.h
> @@ -62,6 +62,7 @@
>  #define V4L2_CTRL_CLASS_FM_RX		0x00a10000	/* FM Receiver controls */
>  #define V4L2_CTRL_CLASS_RF_TUNER	0x00a20000	/* RF tuner controls */
>  #define V4L2_CTRL_CLASS_DETECT		0x00a30000	/* Detection controls */
> +#define V4L2_CTRL_CLASS_VOICE_COIL	0x00a40000	/* Voice coil lens driver controls */
>  
>  /* User-class control IDs */
>  
> @@ -894,6 +895,13 @@ enum v4l2_jpeg_chroma_subsampling {
>  #define V4L2_CID_TEST_PATTERN			(V4L2_CID_IMAGE_PROC_CLASS_BASE + 3)
>  #define V4L2_CID_DEINTERLACING_MODE		(V4L2_CID_IMAGE_PROC_CLASS_BASE + 4)
>  
> +/* Voice coil lens driver controls */
> +
> +#define V4L2_CID_VOICE_COIL_CLASS_BASE		(V4L2_CTRL_CLASS_VOICE_COIL | 0x900)
> +#define V4L2_CID_VOICE_COIL_CLASS		(V4L2_CTRL_CLASS_VOICE_COIL | 1)
> +
> +#define V4L2_CID_VOICE_COIL_CURRENT		(V4L2_CID_VOICE_COIL_CLASS_BASE + 1)
> +
>  
>  /*  DV-class control IDs defined by V4L2 */
>  #define V4L2_CID_DV_CLASS_BASE			(V4L2_CTRL_CLASS_DV | 0x900)



Thanks,
Mauro