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

[Hans de Goede <hansg@kernel.org>]

Hi,

On 28-Sep-26 13:12, Ricardo Ribalda wrote:
> Hi Hans
> 
> On Mon, 28 Sept 2026 at 13:01, Hans de Goede <hansg@kernel.org> 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@gmail.com/
>>
>> Michael, thank you for the patch. Patches 1/2 look good to me:
>>
>> Reviewed-by: Hans de Goede <johannes.goede@oss.qualcomm.com>
>>
>> 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)

Ok, fair enough lets go with this series as is then.

I'll go and merge these 3 patches into uvc/for-next sometime today.

Regards,

Hans