Re: [PATCH v14 11/11] media: uvcvideo: document UVC v1.5 ROI

Laurent Pinchart
2023-12-08T16:00:51Z

Hi Yunke,

Thank you for the patch.

On Fri, Dec 01, 2023 at 04:19:02PM +0900, Yunke Cao wrote:
> Added documentation of V4L2_CID_UVC_REGION_OF_INTEREST_RECT and
> V4L2_CID_UVC_REGION_OF_INTEREST_AUTO.

It would be useful to point here to the userspace code that uses those
controls. A link to the appropriate Chrome OS git tree would be useful,
to showcase a real user.

> Reviewed-by: Ricardo Ribalda <ribalda@chromium.org>
> Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> Signed-off-by: Yunke Cao <yunkec@google.com>
> ---
> Changelog since v11:
> - No change.
> Changelog since v10:
> - Added Reviewed-by from Sergey.
> Changelog since v9:
> - No change.
> Changelog since v8:
> - No change.
> Changelog since v7:
> - Fix documentation for automatic exposure based on comment in v7.
>
> .../userspace-api/media/drivers/uvcvideo.rst | 62 +++++++++++++++++++
> 1 file changed, 62 insertions(+)
>
> diff --git a/Documentation/userspace-api/media/drivers/uvcvideo.rst b/Documentation/userspace-api/media/drivers/uvcvideo.rst
> index aab4304e6bb5..3dc062221f8b 100644
> --- a/Documentation/userspace-api/media/drivers/uvcvideo.rst
> +++ b/Documentation/userspace-api/media/drivers/uvcvideo.rst
> @@ -181,6 +181,7 @@ Argument: struct uvc_xu_control_mapping
> UVC_CTRL_DATA_TYPE_BOOLEAN Boolean
> UVC_CTRL_DATA_TYPE_ENUM Enumeration
> UVC_CTRL_DATA_TYPE_BITMASK Bitmask
> + UVC_CTRL_DATA_TYPE_RECT Rectangular area
>
>
> UVCIOC_CTRL_QUERY - Query a UVC XU control
> @@ -255,3 +256,64 @@ Argument: struct uvc_xu_control_query
> __u8 query Request code to send to the device
> __u16 size Control data size (in bytes)
> __u8 *data Control value
> +
> +
> +Driver-specific V4L2 controls
> +-----------------------------
> +
> +The uvcvideo driver implements the following UVC-specific controls:
> +
> +``V4L2_CID_UVC_REGION_OF_INTEREST_RECT (struct)``
> + This control determines the region of interest (ROI). ROI is a
> + rectangular area represented by a struct :c:type:`v4l2_rect`. The
> + rectangle is in global sensor coordinates and pixel units. It is
> + independent of the field of view, not impacted by any cropping or
> + scaling.
> +
> + Use ``V4L2_CTRL_WHICH_MIN_VAL`` and ``V4L2_CTRL_WHICH_MAX_VAL`` to query
> + the range of rectangle sizes. The left/top coordinates of a minimum or
> + maximum rectangle are always 0. For example, a device can have a minimum
> + ROI rectangle of 1x1@0x0 and a maximum of 640x480@0x0.

Is that actually true ? The UVC 1.5 specification states

GET_MAX shall return the current Window as specified by
CT_DIGITAL_WINDOW_CONTROL.

And the window can have non-zero left and right coordinates.

> +
> + Setting a ROI allows the camera to optimize the capture for the region.
> + The value of ``V4L2_CID_REGION_OF_INTEREST_AUTO`` control determines
> + the detailed behavior.
> +
> +
> +``V4L2_CID_UVC_REGION_OF_INTEREST_AUTO (bitmask)``
> + This determines which, if any, on board features should track to the

s/on board/on-board/

> + Region of Interest specified by the current value of
> + ``V4L2_CID_UVD__REGION_OF_INTEREST_RECT``.
> +
> + Max value is a mask indicating all supported Auto Controls.
> +
> +.. flat-table::
> + :header-rows: 0
> + :stub-columns: 0
> +
> + * - ``V4L2_UVC_REGION_OF_INTEREST_AUTO_EXPOSURE``
> + - Setting this to true causes automatic exposure to track the region of

Maybe "Setting this bit causes..." as those values are bit flags, not
booleans. Same below.

> + interest instead of the whole image.
> + * - ``V4L2_UVC_REGION_OF_INTEREST_AUTO_IRIS``
> + - Setting this to true causes automatic iris to track the region of
> + interest instead of the whole image.
> + * - ``V4L2_UVC_REGION_OF_INTEREST_AUTO_WHITE_BALANCE``
> + - Setting this to true causes automatic white balance to track the region
> + of interest instead of the whole image.
> + * - ``V4L2_UVC_REGION_OF_INTEREST_AUTO_FOCUS``
> + - Setting this to true causes automatic focus adjustment to track the
> + region of interest instead of the whole image.
> + * - ``V4L2_UVC_REGION_OF_INTEREST_AUTO_FACE_DETECT``
> + - Setting this to true causes automatic face detection to track the
> + region of interest instead of the whole image.
> + * - ``V4L2_UVC_REGION_OF_INTEREST_AUTO_DETECT_AND_TRACK``
> + - Setting this to true enables automatic face detection and tracking. The
> + current value of ``V4L2_CID_REGION_OF_INTEREST_RECT`` may be updated by
> + the driver.
> + * - ``V4L2_UVC_REGION_OF_INTEREST_AUTO_IMAGE_STABILIZATION``
> + - Setting this to true enables automatic image stabilization. The
> + current value of ``V4L2_CID_REGION_OF_INTEREST_RECT`` may be updated by
> + the driver.
> + * - ``V4L2_UVC_REGION_OF_INTEREST_AUTO_HIGHER_QUALITY``
> + - Setting this to true enables automatically capture the specified region

I wonder what this means, the UVC 1.5 specification doesn't document
this bit clearly :-(

> + with higher quality if possible.

--
Regards,

Laurent Pinchart