Re: [PATCH v2 3/3] media: uvcvideo: fix up missing AUTO_UPDATE on the OBSBOT Tiny 2
From: Ricardo Ribalda
Date: Wed Sep 02 2026 - 02:36:00 EST
Hi Michael
Thanks for your patch:
On Wed, 2 Sept 2026 at 02:26, Michael Jordan <jordan.mymail@xxxxxxxxx> wrote:
>
> The OBSBOT Tiny 2 (3564:fef8) computes its GET_INFO capability byte per
> control, but gets it wrong for the controls that matter most on a
> motorised PTZ camera: CT_PANTILT_ABSOLUTE, CT_PANTILT_RELATIVE and
> CT_ZOOM_ABSOLUTE all answer 0x03 -- GET and SET capable, with the
> AUTOUPDATE bit clear. (The byte is not a constant stub: CT_ZOOM_RELATIVE
> correctly reports 0x0f, CT_ROLL_ABSOLUTE reports 0x01.)
> uvc_ctrl_get_flags() takes the flags from that byte, so it clears the
> UVC_CTRL_FLAG_AUTO_UPDATE that the static uvc_ctrls[] entries set for
> all three controls. Without AUTO_UPDATE nothing clears ctrl->loaded
> after the first read, so uvcvideo serves them from its cache
> indefinitely: VIDIOC_G_CTRL returns the last value the host commanded,
> never the live one.
>
> All three controls were verified on the hardware to change autonomously
> and to report the live value on GET_CUR:
>
> - pan/tilt position keeps changing for the seconds a commanded gimbal
> move takes, and changes on its own under the camera's autonomous
> subject tracking;
> - zoom follows the subject under the camera's AI framing (observed
> 0-71% with the host issuing no zoom request, matching the vendor
> status protocol's zoom report);
> - the pan/tilt speed control reports the actual current speed during a
> relative move (a commanded 80 reads back as 78, then the deceleration
> ramp, then 0 once the gimbal reaches the end stop). Without
> AUTO_UPDATE the cache would report the written speed forever.
>
> Add fixup entries restoring AUTO_UPDATE, alongside the flags each
> control already has in uvc_ctrls[], for these three controls. The fixup
> replaces info->flags wholesale rather than OR-ing, so each entry spells
> out the full flag set.
>
> The camera's other AUTO_UPDATE-flagged controls were checked and
> deliberately left alone: exposure, white balance and focus have working
> autos, but their GET_CUR just echoes the last SET_CUR (the firmware
> never reports the auto-chosen value), so AUTO_UPDATE would add USB
> traffic for no benefit; there is no auto-hue; CT_ZOOM_RELATIVE already
> reports AUTOUPDATE; CT_ROLL_ABSOLUTE is read-only and unmapped.
>
> 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
>
Reviewed-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
Link: https://lore.kernel.org/linux-media/20260902002544.34798-1-jordan.mymail@xxxxxxxxx/T/#mf4b518b5bfa604a5c925d23d1653b927b811488e
> Suggested-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> Signed-off-by: Michael Jordan <jordan.mymail@xxxxxxxxx>
> ---
> drivers/media/usb/uvc/uvc_ctrl.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> index 64c90c380..74f6e8039 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -2876,6 +2876,26 @@ static bool 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 reports GET|SET without AUTOUPDATE
> + * for the pan/tilt and zoom controls, clearing the AUTO_UPDATE
> + * the driver's own control table sets for them. The device
> + * moves all three on its own (gimbal moves take seconds, and
> + * its autonomous subject tracking pans, tilts and zooms with
> + * no host involvement) and reports the live values on GET_CUR.
> + */
> + { { 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 },
> + { { USB_DEVICE(0x3564, 0xfef8) }, 1,
> + UVC_CT_PANTILT_RELATIVE_CONTROL,
> + UVC_CTRL_FLAG_SET_CUR | UVC_CTRL_FLAG_GET_RANGE |
> + UVC_CTRL_FLAG_AUTO_UPDATE },
> + { { USB_DEVICE(0x3564, 0xfef8) }, 1,
> + UVC_CT_ZOOM_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
>
--
Ricardo Ribalda