linux-kernel - Re: [PATCH v2] V4L: uvcvideo: Add support for relative pan/tilt controls

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Message-ID: <CAP_ceTxk=OE3UVhNKk+WV7EG3E9Z0cOH4tZBU210Awa15OOjgw@mail.gmail.com>
Date:	Tue, 8 Jul 2014 16:28:16 -0700
From:	Vincent Palatin <vpalatin@...omium.org>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:	Pawel Osciak <posciak@...omium.org>,
	Hans de Goede <hdegoede@...hat.com>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Olof Johansson <olofj@...omium.org>,
	Zach Kuznia <zork@...omium.org>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>
Subject: Re: [PATCH v2] V4L: uvcvideo: Add support for relative pan/tilt controls

On Wed, Jun 25, 2014 at 2:54 AM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> Hi Pawel,
>
> On Wednesday 25 June 2014 11:46:24 Pawel Osciak wrote:
>> On Tue, Jun 17, 2014 at 11:45 PM, Vincent Palatin wrote:
>> > Map V4L2_CID_TILT_RELATIVE and V4L2_CID_PAN_RELATIVE to the standard UVC
>> > CT_PANTILT_RELATIVE_CONTROL terminal control request.
>> >
>> > Tested by plugging a Logitech ConferenceCam C3000e USB camera
>> > and controlling pan/tilt from the userspace using the VIDIOC_S_CTRL ioctl.
>> > Verified that it can pan and tilt at the same time in both directions.
>> >
>> > Signed-off-by: Vincent Palatin <vpalatin@...omium.org>
>> >
>> > Change-Id: I7b70b228e5c0126683f5f0be34ffd2807f5783dc
>> > ---
>> >
>> > Changes
>> > v2: fix control request name in description.
>>
>> The patch looks good, but I have a more general comment for everyone to
>> consider. This doesn't match the expected functionality of
>> controls V4L2_CID_PAN/TILT_RELATIVE. This is basically an on/off switch for
>> pan/tilt, which once enabled will keep going until turned off (or I'm
>> guessing until the maximum pan/tilt is reached), while the controls are
>> supposed to expose an ability to turn the camera by a specified amount.
>> Here the amount will also be ignored...
>
> I agree with you here, and this mismatch between the V4L and UVC controls is
> the reason why I haven't implemented relative pan/tilt support.
>
>> Given that this is a standard UVC control, perhaps we need new V4L2
>> controls for it, as I'm assuming we can't change the meaning of existing
>> controls?
>
> We could extend the meaning of the controls to cover the UVC behaviour in a
> device-specific fashion, but that would be confusing for applications, so new
> controls might be a better idea.

Ok, I will add another patch to create new V4L2_CID_PAN_SPEED /
V4L2_CID_TILT_SPEED controls.

-- 
Vincent
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