linux-kernel - Re: [PATCH v2 10/12] media: uvcvideo: Add get_* functions to uvc

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Message-ID: <20250715193505.GB19299@pendragon.ideasonboard.com>
Date: Tue, 15 Jul 2025 22:35:05 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Ricardo Ribalda <ribalda@...omium.org>
Cc: Hans de Goede <hdegoede@...hat.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Hans Verkuil <hverkuil@...all.nl>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Bartosz Golaszewski <brgl@...ev.pl>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	devicetree@...r.kernel.org, linux-gpio@...r.kernel.org,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH v2 10/12] media: uvcvideo: Add get_* functions to
 uvc_entity

On Mon, Jul 14, 2025 at 05:46:40PM +0200, Ricardo Ribalda wrote:
> On Mon, 14 Jul 2025 at 16:30, Laurent Pinchart wrote:
> > On Tue, Jul 01, 2025 at 01:13:10PM +0200, Ricardo Ribalda wrote:
> > > On Sun, 29 Jun 2025 at 20:13, Laurent Pinchart wrote:
> > > > On Thu, Jun 05, 2025 at 05:53:03PM +0000, Ricardo Ribalda wrote:
> > > > > Virtual entities need to provide more values than get_cur and get_cur
> > > >
> > > > I think you meant "get_info and get_cur".
> > > >
> > > > > for their controls. Add support for get_def, get_min, get_max and
> > > > > get_res.
> > > >
> > > > Do they ? The UVC specification defines controls that don't list
> > > > GET_DEF, GET_MIN, GET_MAX and GET_RES as mandatory requests. Can't we do
> > > > the same for the software controls ? This patch is meant to support the
> > > > UVC_SWENTITY_ORIENTATION and UVC_SWENTITY_ROTATION control in the next
> > > > patch, and those are read-only controls. Aren't GET_INFO and GET_CUR
> > > > enough ?
> > >
> > > V4L2_CID_CAMERA_ROTATION has the type UVC_CTRL_DATA_TYPE_UNSIGNED,
> > > that time requires get_min and get_max.
> >
> > Where does that requirement come from ? Is it because how the
> > corresponding V4L2 type (V4L2_CTRL_TYPE_INTEGER) is handled in
> > uvc_ctrl_clamp() ? uvc_ctrl_clamp() is only called when setting a
> > control, from uvc_ctrl_set(), and V4L2_CID_CAMERA_ROTATION should be
> > read-only.
> 
> It its for VIDIOC_QUERY_EXT_CTRL
> 
> uvc_query_v4l2_ctrl -> __uvc_query_v4l2_ctrl -> __uvc_queryctrl_boundaries
> 
> We need to list the min, max, def and step for every control. They are
> fetched with uvc_ctrl_populate_cache()

Ah, I see, thanks.

For GET_RES, I think we can leave it unimplemented.
__uvc_queryctrl_boundaries() will set v4l2_ctrl->step = 0 which seems to
be the right behaviour for a read-only control whose value never
changes.

As for the minimum and maximum, they are currently set to 0 if the
corresponding operations are not supported. I wonder if we should set
them to the current value instead for read-only controls (as in controls
whose flags report support for GET_CUR only)..

> > > We can create a new type UVC_CTRL_DATA_TYPE_UNSIGNED_READ_ONLY that
> > > fakes min, max and res, but I think that it is cleaner this approach.
> > >
> > > > > This is a preparation patch.
> > > > >
> > > > > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > > > > ---
> > > > >  drivers/media/usb/uvc/uvc_ctrl.c | 12 ++++++++++++
> > > > >  drivers/media/usb/uvc/uvcvideo.h |  8 ++++++++
> > > > >  2 files changed, 20 insertions(+)
> > > > >
> > > > > diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> > > > > index 21ec7b978bc7aca21db7cb8fd5d135d876f3330c..59be62ae24a4219fa9d7aacf2ae7382c95362178 100644
> > > > > --- a/drivers/media/usb/uvc/uvc_ctrl.c
> > > > > +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> > > > > @@ -596,6 +596,18 @@ static int uvc_ctrl_query_entity(struct uvc_device *dev,
> > > > >       if (query == UVC_GET_CUR && ctrl->entity->get_cur)
> > > > >               return ctrl->entity->get_cur(dev, ctrl->entity,
> > > > >                                            ctrl->info.selector, data, len);
> > > > > +     if (query == UVC_GET_DEF && ctrl->entity->get_def)
> > > > > +             return ctrl->entity->get_def(dev, ctrl->entity,
> > > > > +                                          ctrl->info.selector, data, len);
> > > > > +     if (query == UVC_GET_MIN && ctrl->entity->get_min)
> > > > > +             return ctrl->entity->get_min(dev, ctrl->entity,
> > > > > +                                          ctrl->info.selector, data, len);
> > > > > +     if (query == UVC_GET_MAX && ctrl->entity->get_max)
> > > > > +             return ctrl->entity->get_max(dev, ctrl->entity,
> > > > > +                                          ctrl->info.selector, data, len);
> > > > > +     if (query == UVC_GET_RES && ctrl->entity->get_res)
> > > > > +             return ctrl->entity->get_res(dev, ctrl->entity,
> > > > > +                                          ctrl->info.selector, data, len);
> > > > >       if (query == UVC_GET_INFO && ctrl->entity->get_info)
> > > > >               return ctrl->entity->get_info(dev, ctrl->entity,
> > > > >                                             ctrl->info.selector, data);
> > > > > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > > > > index a931750bdea25b9062dcc7644bf5f2ed89c1cb4c..d6da8ed3ad4cf3377df49923e051fe04d83d2e38 100644
> > > > > --- a/drivers/media/usb/uvc/uvcvideo.h
> > > > > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > > > > @@ -261,6 +261,14 @@ struct uvc_entity {
> > > > >                       u8 cs, u8 *caps);
> > > > >       int (*get_cur)(struct uvc_device *dev, struct uvc_entity *entity,
> > > > >                      u8 cs, void *data, u16 size);
> > > > > +     int (*get_def)(struct uvc_device *dev, struct uvc_entity *entity,
> > > > > +                    u8 cs, void *data, u16 size);
> > > > > +     int (*get_min)(struct uvc_device *dev, struct uvc_entity *entity,
> > > > > +                    u8 cs, void *data, u16 size);
> > > > > +     int (*get_max)(struct uvc_device *dev, struct uvc_entity *entity,
> > > > > +                    u8 cs, void *data, u16 size);
> > > > > +     int (*get_res)(struct uvc_device *dev, struct uvc_entity *entity,
> > > > > +                    u8 cs, void *data, u16 size);
> > > > >
> > > > >       unsigned int ncontrols;
> > > > >       struct uvc_control *controls;

-- 
Regards,

Laurent Pinchart