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

[Hans de Goede]

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?

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(-)
>