Re: [PATCH v2 10/12] media: uvcvideo: Add get_* functions to uvc_entity

[Ricardo Ribalda <ribalda@chromium.org>]

On Tue, 15 Jul 2025 at 21:35, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> 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.

That will break v4l2-compatiblity. Step needs to be != 0
https://git.linuxtv.org/v4l-utils.git/tree/utils/v4l2-compliance/v4l2-test-controls.cpp#n77

Control ioctls (Input 0):
                fail: v4l2-test-controls.cpp(77): step == 0
                fail: v4l2-test-controls.cpp(201): invalid control 009a0923

>
> 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)..

I am not sure that I like that approach IMO the code looks worse...
but if you prefer that, we can go that way


diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
index ec472e111248..47224437018b 100644
--- a/drivers/media/usb/uvc/uvc_ctrl.c
+++ b/drivers/media/usb/uvc/uvc_ctrl.c
@@ -35,6 +35,8 @@
 /* ------------------------------------------------------------------------
  * Controls
  */
+static int __uvc_ctrl_load_cur(struct uvc_video_chain *chain,
+                              struct uvc_control *ctrl);

 static const struct uvc_control_info uvc_ctrls[] = {
        {
@@ -1272,6 +1274,13 @@ static int uvc_ctrl_populate_cache(struct
uvc_video_chain *chain,
                                        uvc_ctrl_data(ctrl, UVC_CTRL_DATA_DEF));
                if (ret < 0)
                        return ret;
+       } else if (!(ctrl->info.flags & UVC_CTRL_FLAG_SET_CUR)) {
+               ret = __uvc_ctrl_load_cur(chain, ctrl);
+               if (!ret) {
+                       memcpy(uvc_ctrl_data(ctrl, UVC_CTRL_DATA_DEF),
+                              uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT),
+                              ctrl->info.size);
+               }
        }

        if (ctrl->info.flags & UVC_CTRL_FLAG_GET_MIN) {
@@ -1279,14 +1288,31 @@ static int uvc_ctrl_populate_cache(struct
uvc_video_chain *chain,
                                        uvc_ctrl_data(ctrl, UVC_CTRL_DATA_MIN));
                if (ret < 0)
                        return ret;
+       } else if (!(ctrl->info.flags & UVC_CTRL_FLAG_SET_CUR)) {
+               ret = __uvc_ctrl_load_cur(chain, ctrl);
+               if (!ret) {
+                       memcpy(uvc_ctrl_data(ctrl, UVC_CTRL_DATA_MIN),
+                              uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT),
+                              ctrl->info.size);
+               }
        }
+
        if (ctrl->info.flags & UVC_CTRL_FLAG_GET_MAX) {
                ret = uvc_ctrl_query_entity(chain->dev, ctrl, UVC_GET_MAX,
                                        uvc_ctrl_data(ctrl, UVC_CTRL_DATA_MAX));
                if (ret < 0)
                        return ret;
+       } else if (!(ctrl->info.flags & UVC_CTRL_FLAG_SET_CUR)) {
+               ret = __uvc_ctrl_load_cur(chain, ctrl);
+               if (!ret) {
+                       memcpy(uvc_ctrl_data(ctrl, UVC_CTRL_DATA_MAX),
+                              uvc_ctrl_data(ctrl, UVC_CTRL_DATA_CURRENT),
+                              ctrl->info.size);
+               }
        }
+
        if (ctrl->info.flags & UVC_CTRL_FLAG_GET_RES) {
+               u8 *res;
                ret = uvc_ctrl_query_entity(chain->dev, ctrl, UVC_GET_RES,
                                        uvc_ctrl_data(ctrl, UVC_CTRL_DATA_RES));
                if (ret < 0) {
@@ -1304,7 +1330,13 @@ static int uvc_ctrl_populate_cache(struct
uvc_video_chain *chain,
                                      "an XU control. Enabling workaround.\n");
                        memset(uvc_ctrl_data(ctrl, UVC_CTRL_DATA_RES), 0,
                               ctrl->info.size);
+                       res = uvc_ctrl_data(ctrl, UVC_CTRL_DATA_RES);
+                       *res = 1
                }
+       } else {
+               memset(uvc_ctrl_data(ctrl, UVC_CTRL_DATA_RES), 0,
ctrl->info.size);
+               res = uvc_ctrl_data(ctrl, UVC_CTRL_DATA_RES);
+               *res = 1;
        }

        ctrl->cached = 1;
@@ -1541,11 +1573,8 @@ static int __uvc_queryctrl_boundaries(struct
uvc_video_chain *chain,
                        return ret;
        }

-       if (ctrl->info.flags & UVC_CTRL_FLAG_GET_DEF)
                v4l2_ctrl->default_value = uvc_mapping_get_s32(mapping,
                                UVC_GET_DEF, uvc_ctrl_data(ctrl,
UVC_CTRL_DATA_DEF));
-       else
-               v4l2_ctrl->default_value = 0;

        switch (mapping->v4l2_type) {
        case V4L2_CTRL_TYPE_MENU:
@@ -1576,23 +1605,14 @@ static int __uvc_queryctrl_boundaries(struct
uvc_video_chain *chain,
                break;
        }

-       if (ctrl->info.flags & UVC_CTRL_FLAG_GET_MIN)
-               v4l2_ctrl->minimum = uvc_mapping_get_s32(mapping, UVC_GET_MIN,
-                               uvc_ctrl_data(ctrl, UVC_CTRL_DATA_MIN));
-       else
-               v4l2_ctrl->minimum = 0;
+       v4l2_ctrl->minimum = uvc_mapping_get_s32(mapping, UVC_GET_MIN,
+                                       uvc_ctrl_data(ctrl, UVC_CTRL_DATA_MIN));

-       if (ctrl->info.flags & UVC_CTRL_FLAG_GET_MAX)
-               v4l2_ctrl->maximum = uvc_mapping_get_s32(mapping, UVC_GET_MAX,
-                               uvc_ctrl_data(ctrl, UVC_CTRL_DATA_MAX));
-       else
-               v4l2_ctrl->maximum = 0;
+       v4l2_ctrl->maximum = uvc_mapping_get_s32(mapping, UVC_GET_MAX,
+                                       uvc_ctrl_data(ctrl, UVC_CTRL_DATA_MAX));

-       if (ctrl->info.flags & UVC_CTRL_FLAG_GET_RES)
-               v4l2_ctrl->step = uvc_mapping_get_s32(mapping, UVC_GET_RES,
-                               uvc_ctrl_data(ctrl, UVC_CTRL_DATA_RES));
-       else
-               v4l2_ctrl->step = 0;
+       v4l2_ctrl->step = uvc_mapping_get_s32(mapping, UVC_GET_RES,
+                                       uvc_ctrl_data(ctrl, UVC_CTRL_DATA_RES));

        return 0;
 }

>
> > > > 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@chromium.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



-- 
Ricardo Ribalda