[PATCH 3/3] media: uvcvideo: fix up missing AUTO_UPDATE on OBSBOT Tiny 2 pan/tilt

[Michael Jordan <jordan.mymail@gmail.com>]

The OBSBOT Tiny 2 (3564:fef8) answers GET_INFO for CT_PANTILT_ABSOLUTE
(entity 1, selector 0x0d) with 0x03 -- GET and SET capable, but with the
AUTOUPDATE bit clear. It returns the same 0x03 for every Camera Terminal
control queried, so the firmware is not computing the byte per control.
uvc_ctrl_get_flags() takes the flags from that byte, so it clears the
UVC_CTRL_FLAG_AUTO_UPDATE that the static uvc_ctrls[] entry sets for
this control. Without AUTO_UPDATE nothing clears ctrl->loaded after the
first read, so uvcvideo serves the control from its cache indefinitely:
VIDIOC_G_CTRL returns the last value the host commanded, never the
actuator's live position. On a motorised PTZ camera the position keeps
changing during a move, and changes on its own under the camera's
autonomous subject tracking, so userspace cannot observe it at all.

Add a flags fixup entry restoring AUTO_UPDATE, alongside the flags the
control already has, for this camera's pan/tilt control. With
AUTO_UPDATE restored, the rollback at the end of every
VIDIOC_G_EXT_CTRLS runs uvc_ctrl_commit_entity(), which clears
ctrl->loaded, so the next read re-queries the device and reports the
live position. The fixup replaces info->flags wholesale rather than
OR-ing, so the entry spells out the full flag set for the control.

Tested on an OBSBOT Tiny 2: without this, a read taken while the gimbal
is moving (or after the gimbal is moved by hand) returns a stale value;
with it, VIDIOC_G_EXT_CTRLS tracks the physical position on both axes.

The vendor has been asked to fix the firmware (support ticket #8220,
2026-08-04); no fix is available at the time of writing.

lsusb -v (device descriptor and the Camera Terminal):

  Bus 003 Device 006: ID 3564:fef8 Remo Tech Co., Ltd. OBSBOT Tiny 2
  Device Descriptor:
    bLength                18
    bDescriptorType         1
    bcdUSB               2.10
    bDeviceClass          239 Miscellaneous Device
    bDeviceSubClass         2 [unknown]
    bDeviceProtocol         1 Interface Association
    bMaxPacketSize0        64
    idVendor           0x3564 Remo Tech Co., Ltd.
    idProduct          0xfef8 OBSBOT Tiny 2
    bcdDevice            4.09
    iManufacturer           1 Remo Tech Co., Ltd.
    iProduct                2 OBSBOT Tiny 2
    iSerial                 0
    bNumConfigurations      1
  [...]
        VideoControl Interface Descriptor:
          bLength                18
          bDescriptorType        36
          bDescriptorSubtype      2 (INPUT_TERMINAL)
          bTerminalID             1
          wTerminalType      0x0201 Camera Sensor
          bAssocTerminal          0
          iTerminal               0
          wObjectiveFocalLengthMin      0
          wObjectiveFocalLengthMax      0
          wOcularFocalLength            0
          bControlSize                  3
          bmControls           0x00023e3e
            Auto-Exposure Mode
            Auto-Exposure Priority
            Exposure Time (Absolute)
            Exposure Time (Relative)
            Focus (Absolute)
            Zoom (Absolute)
            Zoom (Relative)
            PanTilt (Absolute)
            PanTilt (Relative)
            Roll (Absolute)
            Focus, Auto

Suggested-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Michael Jordan <jordan.mymail@gmail.com>
---
 drivers/media/usb/uvc/uvc_ctrl.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
index b16a5cc0d..379ee51bd 100644
--- a/drivers/media/usb/uvc/uvc_ctrl.c
+++ b/drivers/media/usb/uvc/uvc_ctrl.c
@@ -2876,6 +2876,15 @@ static void uvc_ctrl_fixup_flags(struct uvc_device *dev,
 			UVC_CTRL_FLAG_GET_MIN | UVC_CTRL_FLAG_GET_MAX |
 			UVC_CTRL_FLAG_GET_DEF | UVC_CTRL_FLAG_SET_CUR |
 			UVC_CTRL_FLAG_AUTO_UPDATE },
+		/*
+		 * OBSBOT Tiny 2: GET_INFO on CT_PANTILT_ABSOLUTE_CONTROL is a
+		 * stub that reports GET|SET only, clearing the AUTO_UPDATE the
+		 * driver's own control table sets for this control.
+		 */
+		{ { USB_DEVICE(0x3564, 0xfef8) }, 1,
+			UVC_CT_PANTILT_ABSOLUTE_CONTROL,
+			UVC_CTRL_FLAG_SET_CUR | UVC_CTRL_FLAG_GET_RANGE |
+			UVC_CTRL_FLAG_RESTORE | UVC_CTRL_FLAG_AUTO_UPDATE },
 	};
 
 	unsigned int i;
-- 
2.43.0