Re: [PATCH v7 7/7] media: uvcvideo: document UVC v1.5 ROI

Yunke Cao
2022-09-20T07:47:42Z

Hi Laurent,

Thanks for the review!

On Thu, Aug 25, 2022 at 5:17 AM Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hi Yunke,
>
> Thank you for the patch.
>
> On Tue, Jun 28, 2022 at 04:57:05PM +0900, Yunke Cao wrote:
> > Added documentation of V4L2_CID_UVC_REGION_OF_INTEREST_RECT and
> > V4L2_CID_UVC_REGION_OF_INTEREST_AUTO.
> >
> > Signed-off-by: Yunke Cao <yunkec@google.com>
> > ---
> > .../userspace-api/media/drivers/uvcvideo.rst | 61 +++++++++++++++++++
> > 1 file changed, 61 insertions(+)
> >
> > diff --git a/Documentation/userspace-api/media/drivers/uvcvideo.rst b/Documentation/userspace-api/media/drivers/uvcvideo.rst
> > index a290f9fadae9..ee4c182aa274 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 +256,63 @@ 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
> > +
>
> You can add a second blank line here, as above the "Extension Unit (XU)
> support" title.
>
> > +Private V4L2 controls
>
> "Driver-specific V4L2 controls" would be better, those controls are not
> private.
>
> > +---------------------
> > +
> > +A few UVC specific V4L2 control IDs are listed below.
>
> s/UVC specific/UVC-specific/
>
> But I'd write
>
> 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 an
>
> s/is an/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. For example, a device can have a minimum
> > + ROI rectangle of 1x1@0x0 and a maximum of 640x480@0x0.
>
> Minimum and maximum values for rectangles are ill-defined. Are the top
> and left coordinates always 0 ? If so that should be documented.
>
> > +
> > + 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
> > + 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.
>
> No need to wrap this line.
>
> > +
> > +.. flat-table::
> > + :header-rows: 0
> > + :stub-columns: 0
> > +
> > + * - ``V4L2_REGION_OF_INTEREST_AUTO_EXPOSURE``
>
> s/V4L2/V4L2_UVC/
>
> Same below.
>
> > + - Setting this to true enables automatic exposure time for the specified
>
> s/exposure time/exposure/ (as it can also include gain)
>
> > + region.
>
> It's not that it enables automatic exposure for the specified region, is
> that it causes the automatic exposure to track the region of interest
> instead of the whole image. Same below.
>

I see. Thanks for clarifying. I will update this and the comments above in the
next version.

> > + * - ``V4L2_REGION_OF_INTEREST_AUTO_IRIS``
> > + - Setting this to true enables automatic iris aperture for the specified
> > + region.
> > + * - ``V4L2_REGION_OF_INTEREST_AUTO_WHITE_BALANCE``
> > + - Setting this to true enables automatic white balance adjustment for the
> > + specified region.
> > + * - ``V4L2_REGION_OF_INTEREST_AUTO_FOCUS``
> > + - Setting this to true enables automatic focus adjustment for the
> > + specified region.
> > + * - ``V4L2_REGION_OF_INTEREST_AUTO_FACE_DETECT``
> > + - Setting this to true enables automatic face detection for the
> > + specified region.
> > + * - ``V4L2_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_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.
>
> How so ?

If I read the UVC specification correctly, the ROI rectangles are
volatile when these two
flags are set.
"This RoI should be the same as specified in most recent SET_CUR except in the
case where the ‘Auto Detect and Track’ and/or ‘Image Stabilization’
bit have been set."
(4.2.2.1.20 Digital Region of Interest (ROI) Control)

Maybe it's better to say "updated by the hardware" instead of driver?

>
>
> > + * - ``V4L2_REGION_OF_INTEREST_AUTO_HIGHER_QUALITY``
> > + - Setting this to true enables automatically capture the specified region
> > + with higher quality if possible.
>
> Could you please clarify this one ? I'm not sure to understand what it
> means.

Sorry, it's not very clear to me either... I just added it because there's a
"Higher Quality" in the specification.

Best,
Yunke

>
> --
> Regards,
>
> Laurent Pinchart