Re: [PATCH v2 0/3] media: uvcvideo: live pan/tilt/zoom readback on the OBSBOT Tiny 2

[Ricardo Ribalda]

Hi Hans

On Mon, 28 Sept 2026 at 13:01, Hans de Goede <hansg@xxxxxxxxxx> wrote:
>
> Hi All,
>
> On 2-Sep-26 02:25, Michael Jordan wrote:
> > The OBSBOT Tiny 2's GET_INFO strips the AUTOUPDATE bit from its pan,
> > tilt and zoom controls, so uvcvideo caches them and userspace can never
> > observe the actuator's live state. This series reports AUTO_UPDATE
> > controls as volatile to userspace, generalises the existing XU flags
> > fixup table to all controls, and adds entries for the three affected
> > controls on this camera.
> >
> > Changes in v2 (following Ricardo's review of v1 [1]):
> >
> > - Patch 1: unchanged; picked up Ricardo's Reviewed-by.
> > - Patch 2: uvc_ctrl_fixup_flags() now returns bool and runs at the
> >   start of uvc_ctrl_get_flags(), before the allocation, skipping the
> >   GET_INFO query entirely for controls the table covers (Ricardo).
> > - Patch 3: as asked, I checked whether the camera's other
> >   AUTO_UPDATE-flagged controls suffer the same bug. Two more do:
> >   CT_PANTILT_RELATIVE and CT_ZOOM_ABSOLUTE, both verified on hardware
> >   to change autonomously and report live values on GET_CUR; entries
> >   added for both. Exposure, white balance and focus turned out to be
> >   write-only on this firmware (their autos work, but GET_CUR echoes the
> >   last SET_CUR), so they gain nothing from AUTO_UPDATE and were left
> >   alone; details in the commit message. The commit message also no
> >   longer claims the capability byte is the same for every control --
> >   probing every control showed it is computed per control, just wrong
> >   for the PTZ ones. Dropped Ricardo's Reviewed-by since the patch
> >   changed materially.
> >
> > The full lsusb -v output was posted in reply to v1's patch 3, in the
> > thread at [1].
> >
> > [1] https://lore.kernel.org/linux-media/20260828152557.653475-1-jordan.mymail@xxxxxxxxx/
>
> Michael, thank you for the patch. Patches 1/2 look good to me:
>
> Reviewed-by: Hans de Goede <johannes.goede@xxxxxxxxxxxxxxxx>
>
> Ricardo (and Michael, I wonder, in the light of Michael already having
> found a second camera with the same issue and also in the light of your
> "media: uvcvideo: Automatically handle invalid uvc_versions" series
> if it would not be better to try to fix this up automatically instead
> of relying on device quirks?
>
> Specifically the UVC_CTRL_FLAG_AUTO_UPDATE flag is already there
> in the default flags for these controls (and a bunch of others)
> in uvc_ctrls[].
>
> I wonder if we should simply always honor UVC_CTRL_FLAG_AUTO_UPDATE
> from uvc_ctrls[] even when we do get a valid GET_INFO request and
> simply or in the UVC_CTRL_FLAG_AUTO_UPDATE from uvc_ctrls[] if it
> is there?

I would say that for now we can add quirks, and if we see a big
proliferation of them, we can implement something automatic.

My fear is that bypassing the device flags might trigger errors that
could disable the affected controls.

Since the two devices that Michael mentioned come from the same
manufacturer, I do not think they justify automatic handling just yet.
And who knows maybe OBSBOT will fix their firmware? (Yes I also
believe in Santa)


>
> That avoids needing to adding more and more quirks for this.
>
> Regards,
>
> Hans
>
>
>
>
> > Michael Jordan (3):
> >   media: uvcvideo: report AUTO_UPDATE controls as volatile
> >   media: uvcvideo: generalise the XU flags fixup to all controls
> >   media: uvcvideo: fix up missing AUTO_UPDATE on the OBSBOT Tiny 2
> >
> >  drivers/media/usb/uvc/uvc_ctrl.c | 122 ++++++++++++++++++++-----------
> >  1 file changed, 81 insertions(+), 41 deletions(-)
> >
>


-- 
Ricardo Ribalda