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Date:   Fri, 12 Mar 2021 12:13:49 +0200
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Cc:     Ricardo Ribalda <ribalda@chromium.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Tomasz Figa <tfiga@chromium.org>,
        linux-media <linux-media@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Hans Verkuil <hverkuil@xs4all.nl>
Subject: Re: [PATCH v2 5/6] media: uvcvideo: Add support for
 V4L2_CTRL_TYPE_CTRL_CLASS
Message-ID: <YEs+3fh2zUAeeBQy@pendragon.ideasonboard.com>
References: <20210311221946.1319924-1-ribalda@chromium.org>
 <20210311221946.1319924-6-ribalda@chromium.org>
 <YErCElYk7YhB7dvp@pendragon.ideasonboard.com>
 <CAPybu_2tu_=1HtC1Cfr86uP1A367hnfvO0KXmCbGaYUJ1A2X2Q@mail.gmail.com>
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Hi Ricardo,

On Fri, Mar 12, 2021 at 10:57:33AM +0100, Ricardo Ribalda Delgado wrote:
> On Fri, Mar 12, 2021 at 2:25 AM Laurent Pinchart wrote:
> > On Thu, Mar 11, 2021 at 11:19:45PM +0100, Ricardo Ribalda wrote:
> > > Create all the class controls for the device defined controls.
> > >
> > > Fixes v4l2-compliance:
> > > Control ioctls (Input 0):
> > >               fail: v4l2-test-controls.cpp(216): missing control class for class 00980000
> > >               fail: v4l2-test-controls.cpp(216): missing control tclass for class 009a0000
> > >       test VIDIOC_QUERY_EXT_CTRL/QUERYMENU: FAIL
> > >
> > > Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> > > ---
> > >  drivers/media/usb/uvc/uvc_ctrl.c | 90 ++++++++++++++++++++++++++++++++
> > >  drivers/media/usb/uvc/uvcvideo.h |  7 +++
> > >  2 files changed, 97 insertions(+)
> > >
> > > diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> > > index b3dde98499f4..4e0ed2595ae9 100644
> > > --- a/drivers/media/usb/uvc/uvc_ctrl.c
> > > +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> > > @@ -357,6 +357,17 @@ static const struct uvc_control_info uvc_ctrls[] = {
> > >       },
> > >  };
> > >
> > > +static const struct uvc_control_class uvc_control_class[] = {
> > > +     {
> > > +             .id             = V4L2_CID_CAMERA_CLASS,
> > > +             .name           = "Camera Controls",
> > > +     },
> > > +     {
> > > +             .id             = V4L2_CID_USER_CLASS,
> > > +             .name           = "User Controls",
> > > +     },
> > > +};
> > > +
> > >  static const struct uvc_menu_info power_line_frequency_controls[] = {
> > >       { 0, "Disabled" },
> > >       { 1, "50 Hz" },
> > > @@ -1024,6 +1035,49 @@ static int __uvc_ctrl_get(struct uvc_video_chain *chain,
> > >       return 0;
> > >  }
> > >
> > > +static int __uvc_query_v4l2_class(struct uvc_device *dev, u32 req_id,
> > > +                               u32 found_id)
> > > +{
> > > +     bool find_next = req_id & V4L2_CTRL_FLAG_NEXT_CTRL;
> > > +     int i;
> >
> > unsigned int as i will never be negative.
> 
> Sometimes you are a bit negative with my patches... :)
> 
> (sorry, it is Friday)
>
> > > +
> > > +     req_id &= V4L2_CTRL_ID_MASK;
> > > +
> > > +     for (i = 0; i < ARRAY_SIZE(uvc_control_class); i++) {
> > > +             if (!(dev->ctrl_class_bitmap & BIT(i)))
> > > +                     continue;
> > > +             if (!find_next) {
> > > +                     if (uvc_control_class[i].id == req_id)
> > > +                             return i;
> > > +                     continue;
> > > +             }
> > > +             if ((uvc_control_class[i].id > req_id) &&
> > > +                 (uvc_control_class[i].id < found_id))
> >
> > No need for the inner parentheses.
> >
> > > +                     return i;
> > > +     }
> > > +
> > > +     return -ENODEV;
> > > +}
> > > +
> > > +static int uvc_query_v4l2_class(struct uvc_device *dev, u32 req_id,
> > > +                             u32 found_id, struct v4l2_queryctrl *v4l2_ctrl)
> > > +{
> > > +     int idx;
> > > +
> > > +     idx = __uvc_query_v4l2_class(dev, req_id, found_id);
> > > +     if (idx < 0)
> > > +             return -ENODEV;
> > > +
> > > +     memset(v4l2_ctrl, 0, sizeof(*v4l2_ctrl));
> > > +     v4l2_ctrl->id = uvc_control_class[idx].id;
> > > +     strscpy(v4l2_ctrl->name, uvc_control_class[idx].name,
> > > +             sizeof(v4l2_ctrl->name));
> > > +     v4l2_ctrl->type = V4L2_CTRL_TYPE_CTRL_CLASS;
> > > +     v4l2_ctrl->flags = V4L2_CTRL_FLAG_WRITE_ONLY |
> > > +                                     V4L2_CTRL_FLAG_READ_ONLY;
> >
> >         v4l2_ctrl->flags = V4L2_CTRL_FLAG_WRITE_ONLY
> >                          | V4L2_CTRL_FLAG_READ_ONLY;
> >
> > > +     return 0;
> > > +}
> >
> > If you agree with the comments below, you could inline
> > __uvc_query_v4l2_class() in uvc_query_v4l2_class() as it won't be called
> > separately.
> >
> > > +
> > >  static int __uvc_query_v4l2_ctrl(struct uvc_video_chain *chain,
> > >       struct uvc_control *ctrl,
> > >       struct uvc_control_mapping *mapping,
> > > @@ -1123,6 +1177,14 @@ int uvc_query_v4l2_ctrl(struct uvc_video_chain *chain,
> > >       struct uvc_control_mapping *mapping;
> > >       int ret;
> > >
> > > +     /* Check if the ctrl is a know class */
> > > +     if (!(v4l2_ctrl->id & V4L2_CTRL_FLAG_NEXT_CTRL)) {
> > > +             ret = uvc_query_v4l2_class(chain->dev, v4l2_ctrl->id,
> > > +                                        v4l2_ctrl->id, v4l2_ctrl);
> >
> > You could pass 0 for found_id here.
> >
> > > +             if (!ret)
> > > +                     return 0;
> > > +     }
> > > +
> >
> > Should this be done with the chain->ctrl_mutex locked, as
> > __uvc_query_v4l2_class() accesses dev->ctrl_class_bitmap that could be
> > modified concurrently ?
> >
> > >       ret = mutex_lock_interruptible(&chain->ctrl_mutex);
> > >       if (ret < 0)
> > >               return -ERESTARTSYS;
> > > @@ -1133,6 +1195,13 @@ int uvc_query_v4l2_ctrl(struct uvc_video_chain *chain,
> > >               goto done;
> > >       }
> > >
> >
> > A comment here along the lines of
> >
> >         /*
> >          * If we're enumerating control with V4L2_CTRL_FLAG_NEXT_CTRL, check if
> >          * a class should be inserted between the previous control and the one
> >          * we have just found.
> >          */
> >
> > could be useful, as it's not trivial.
> 
> yes, it looks better thanks!
> 
> > > +     if (v4l2_ctrl->id & V4L2_CTRL_FLAG_NEXT_CTRL) {
> > > +             ret = uvc_query_v4l2_class(chain->dev, v4l2_ctrl->id,
> > > +                                        mapping->id, v4l2_ctrl);
> > > +             if (!ret)
> > > +                     goto done;
> > > +     }
> > > +
> > >       ret = __uvc_query_v4l2_ctrl(chain, ctrl, mapping, v4l2_ctrl);
> > >  done:
> > >       mutex_unlock(&chain->ctrl_mutex);
> > > @@ -1422,6 +1491,9 @@ static int uvc_ctrl_add_event(struct v4l2_subscribed_event *sev, unsigned elems)
> > >       struct uvc_control *ctrl;
> > >       int ret;
> > >
> > > +     if (__uvc_query_v4l2_class(handle->chain->dev, sev->id, 0) >= 0)
> > > +             return 0;
> >
> > Do we really need to succeed ? What's the point in subscribing for
> > control change events on a class ? Can't we just check if sev->id is a
> > class, and return -EINVAL in that case ?
> 
> Unfortunately it is expected that you can subscribe to all the events,
> even the ctrl_classes
>         test VIDIOC_G/S/TRY_EXT_CTRLS: OK
>                 fail: v4l2-test-controls.cpp(835): subscribe event for
> control 'User Controls' failed
>         test VIDIOC_(UN)SUBSCRIBE_EVENT/DQEVENT: FAIL

Looks like something that should be dropped from v4l2-compliance,
there's no use case for subscribing to a class.

> > > +
> > >       ret = mutex_lock_interruptible(&handle->chain->ctrl_mutex);
> > >       if (ret < 0)
> > >               return -ERESTARTSYS;
> > > @@ -1458,6 +1530,9 @@ static void uvc_ctrl_del_event(struct v4l2_subscribed_event *sev)
> > >  {
> > >       struct uvc_fh *handle = container_of(sev->fh, struct uvc_fh, vfh);
> > >
> > > +     if (__uvc_query_v4l2_class(handle->chain->dev, sev->id, 0) >= 0)
> > > +             return;
> >
> > And this could then be dropped, as this function won't be called if the
> > subscription failed.
> >
> > > +
> > >       mutex_lock(&handle->chain->ctrl_mutex);
> > >       list_del(&sev->node);
> > >       mutex_unlock(&handle->chain->ctrl_mutex);
> > > @@ -1577,6 +1652,9 @@ int uvc_ctrl_get(struct uvc_video_chain *chain,
> > >       struct uvc_control *ctrl;
> > >       struct uvc_control_mapping *mapping;
> > >
> > > +     if (__uvc_query_v4l2_class(chain->dev, xctrl->id, 0) >= 0)
> > > +             return -EACCES;
> > > +
> > >       ctrl = uvc_find_control(chain, xctrl->id, &mapping);
> > >       if (ctrl == NULL)
> > >               return -EINVAL;
> > > @@ -1596,6 +1674,9 @@ int uvc_ctrl_set(struct uvc_fh *handle,
> > >       s32 max;
> > >       int ret;
> > >
> > > +     if (__uvc_query_v4l2_class(chain->dev, xctrl->id, 0) >= 0)
> > > +             return -EACCES;
> > > +
> >
> > Similarly as in patch 1/6, should these two checks be moved to
> > v4l_s_ctrl() and v4l_s_ext_ctrls(), as it's never valid to get/set a
> > class ?
> 
> I do not think that it is possible, you need to return -EACCESS if the
> control exists and -EINVAL if it does not exist.
> v4l_s_ext_ctrls does not know if the ctrl exists.

*sigh* I'm sad that we need this kind of complexity in drivers because
the API requires us to implement a behaviour that nobody actually cares
about :-( The way classes are implemented is really a big hack.

> > >       ctrl = uvc_find_control(chain, xctrl->id, &mapping);
> > >       if (ctrl == NULL)
> > >               return -EINVAL;
> > > @@ -2062,6 +2143,7 @@ static int __uvc_ctrl_add_mapping(struct uvc_device *dev,
> > >  {
> > >       struct uvc_control_mapping *map;
> > >       unsigned int size;
> > > +     int i;
> >
> > This can be unsigned as i never takes negative values.
> I cannot repeat the same joke... even if it is a bad joke
> >
> > >
> > >       /* Most mappings come from static kernel data and need to be duplicated.
> > >        * Mappings that come from userspace will be unnecessarily duplicated,
> > > @@ -2085,6 +2167,14 @@ static int __uvc_ctrl_add_mapping(struct uvc_device *dev,
> > >       if (map->set == NULL)
> > >               map->set = uvc_set_le_value;
> > >
> > > +     for (i = 0; i < ARRAY_SIZE(uvc_control_class); i++) {
> > > +             if (V4L2_CTRL_ID2WHICH(uvc_control_class[i].id) ==
> > > +                                             V4L2_CTRL_ID2WHICH(map->id)) {
> >
> > You can write this
> >
> >                 if (uvc_control_class[i].id == V4L2_CTRL_ID2WHICH(map->id)) {
> >
> > as the uvc_control_class array contains control classes only.
> 
> Are you sure?
> #define V4L2_CID_CAMERA_CLASS                (V4L2_CTRL_CLASS_CAMERA | 1)
> 
> we are sasing the cid, not the class.

Indeed, my bad.

> > > +                     dev->ctrl_class_bitmap |= BIT(i);
> > > +                     break;
> > > +             }
> > > +     }
> > > +
> > >       list_add_tail(&map->list, &ctrl->info.mappings);
> > >       uvc_dbg(dev, CONTROL, "Adding mapping '%s' to control %pUl/%u\n",
> > >               map->name, ctrl->info.entity, ctrl->info.selector);
> > > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > > index 97df5ecd66c9..63b5d697a438 100644
> > > --- a/drivers/media/usb/uvc/uvcvideo.h
> > > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > > @@ -262,6 +262,11 @@ struct uvc_control_mapping {
> > >                   u8 *data);
> > >  };
> > >
> > > +struct uvc_control_class {
> > > +     u32 id;
> > > +     char name[32];
> > > +};
> > > +
> > >  struct uvc_control {
> > >       struct uvc_entity *entity;
> > >       struct uvc_control_info info;
> > > @@ -707,6 +712,8 @@ struct uvc_device {
> > >       } async_ctrl;
> > >
> > >       struct uvc_entity *gpio_unit;
> > > +
> > > +     u8 ctrl_class_bitmap;
> >
> > Should this be stored in the chain, as different chains can have
> > different controls ?
> >
> > >  };
> > >
> > >  enum uvc_handle_state {

-- 
Regards,

Laurent Pinchart