[linux-uvc-devel] V4L2_CTRL_TYPE_STRING supported in libwebcam, v4l2, but not uvcvideo driver

[Lucas M. <luc...@da...>]

Hi Paulo and Laurent,

I'm developing a UVC camera firmware with extension unit controls and
would like to use V4L2_CTRL_TYPE_STRING and the corresponding
UVC_CTRL_DATA_TYPE_RAW to get around the 4 byte limit of the other XU
control types. Something similar to
https://sourceforge.net/p/libwebcam/code/ci/master/tree/uvcdynctrl/data/046d/logitech.xml#l1630
:

                <mapping>
                        <name>USB Information</name>
                        <uvc>
                                <control_ref
idref="devinfo_usb_information_control_v1"/>
                                <size>48</size>
                                <offset>0</offset>
                                <uvc_type>UVC_CTRL_DATA_TYPE_RAW</uvc_type>
                        </uvc>
                        <v4l2>
                                <id>V4L2_CID_USB_INFO</id>
                                <v4l2_type>V4L2_CTRL_TYPE_STRING</v4l2_type>
                        </v4l2>
                </mapping>

However, even though I rebuilt uvcdynctrl to support
V4L2_CTRL_TYPE_STRING the uvcvideo driver appears to lack support for
mapping this V4L2 data type. For example,
uvc_v4l2.c:uvc_ioctl_ctrl_map() only supports V4L2_CTRL_TYPE_{INTEGER,
BOOLEAN, BUTTON, MENU} (
http://elixir.free-electrons.com/linux/latest/source/drivers/media/usb/uvc/uvc_v4l2.c#L36
).

Is there a patch floating around that adds support that I can test? If
not, I will try adding support since I have a device to test with.
Either way any guidance would be appreciated.

Thanks!