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

Yunke Cao
2023-12-12T04:45:13Z

Hi Laurent,

Thanks for the review!

On Sat, Dec 9, 2023 at 1:00 AM Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> 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.

Does https://source.chromium.org/chromiumos/chromiumos/codesearch/+/main:src/platform2/camera/hal/usb/
work?
Do you think we need the link in both the commit message and this .rst file?

>
> > 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.
>

Ah, you are right. I think I will just remove "The left/top
coordinates of a minimum or maximum rectangle are always 0."

> > +
> > + 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.
>

Sounds good.

> > + 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 :-(
>

I have no idea :-( . I haven't seen any camera module in Chrome OS
attempt to implement this bit, either.

Best,
Yunke

> > + with higher quality if possible.
>
> --
> Regards,
>
> Laurent Pinchart