linux-kernel - Re: [PATCH] uvcvideo: Remo OBSBOT quirk fix for incorrect relative min pan/tilt/zoom speeds

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Date: Tue, 26 Mar 2024 02:07:42 +0100
From: Gergo Koteles <soyer@....hu>
To: johnebgood@...uritylive.com,
  Laurent Pinchart <laurent.pinchart@...asonboard.com>,
  Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
  linh.tp.vu@...il.com, ribalda@...omium.org, John Bauer <john@....co>
Subject: Re: [PATCH] uvcvideo: Remo OBSBOT quirk fix for incorrect relative
 min pan/tilt/zoom speeds

Hi John,

On Mon, 2024-03-25 at 19:38 -0500, John Bauer via B4 Relay wrote:
> From: John Bauer <johnebgood@...uritylive.com>
> 
> The OBSBOT series of cameras misreports the minimum relative
> pan_speed, tilt_speed and zoom_continuous v4l2 controls resulting
> in the inability to control the camera with finesse with an analog
> stick or other programmatic methods. This patch applies to all
> Remo (OBSBOT) vendor cameras with the vendor ID of 0x3564. If the
> vendor fixes the firmware this behavior should still remain valid.
> With this broad vendor fix when new devices are released the kernel
> module won't need to be modified. When the vendor fixes the firmware the
> device list can be modified with finer grained device filters.

I don't think they misreports the values.

The UVC 1.5 spec says:

The bPanRelative field is used to specify the pan direction to move. A
value of 0 indicates to stop the pan, a value of 1 indicates to start
moving clockwise direction, and a value of 0xFF indicates to start
moving counterclockwise direction. <<The GET_DEF, GET_MIN, GET_MAX and
GET_RES requests will return zero for this field.>>

The bTiltRelative field is used to specify the tilt direction to move.
A value of zero indicates to stop the tilt, a value of 1 indicates that
the camera point the imaging plane up, and a value of 0xFF indicates
that the camera point the imaging plane down. <<The GET_DEF, GET_MIN,
GET_MAX and GET_RES requests will return zero for this field.>>

The bZoom field indicates whether the zoom lens group is stopped or the
direction of the zoom lens. A value of 1 indicates that the zoom lens
is moved towards the telephoto direction. A value of zero indicates
that the zoom lens is stopped, and a value of 0xFF indicates that the
zoom lens is moved towards the wide-angle direction. <<The GET_MIN,
GET_MAX, GET_RES and GET_DEF requests will return zero for this
field.>>

So they can't report negative values for GET_MIN, therefore the GET_MIN
of bPanSpeed, bTiltSpeed, b(Zoom)Speed will be the minimum speed of any
direction.

I think it will work with any PTZ camera without the quirk.

Regards,
Gergo