Re: [PATCH v9 16/22] media: uvcvideo: Return -EACCES to inactive controls

[Ricardo Ribalda]

Hi Laurent

Thanks for your review!

On Thu, 10 Jun 2021 at 19:28, Laurent Pinchart
<laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
>
> Hi Ricardo,
>
> Thank you for the patch.
>
> On Fri, Mar 26, 2021 at 10:58:34AM +0100, Ricardo Ribalda wrote:
> > If a control is inactive return -EACCES to let the userspace know that
> > the value will not be applied automatically when the control is active
> > again.
>
> Isn't the device supposed to stall the control set in that case, with
> the bRequestErrorCode set to "Wrong state", which uvc_query_ctrl()
> translates to -EACCES already ? Could you elaborate on why this patch is
> needed ?

The problem is that the hardware was not returning the equivalent of
EACCES, so we had to capture it manually.
I will try to revert the patch and capture an error.

>
> > Suggested-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
> > Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> > ---
> >  drivers/media/usb/uvc/uvc_ctrl.c | 71 +++++++++++++++++++++-----------
> >  1 file changed, 48 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> > index bcebf9d1a46f..d9d4add1e813 100644
> > --- a/drivers/media/usb/uvc/uvc_ctrl.c
> > +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> > @@ -1082,13 +1082,36 @@ static const char *uvc_map_get_name(const struct uvc_control_mapping *map)
> >       return "Unknown Control";
> >  }
> >
> > +static bool uvc_ctrl_is_inactive(struct uvc_video_chain *chain,
> > +                              struct uvc_control *ctrl,
> > +                              struct uvc_control_mapping *mapping)
> > +{
> > +     struct uvc_control_mapping *master_map = NULL;
> > +     struct uvc_control *master_ctrl = NULL;
> > +     s32 val;
> > +     int ret;
> > +
> > +     if (!mapping->master_id)
> > +             return false;
> > +
> > +     __uvc_find_control(ctrl->entity, mapping->master_id, &master_map,
> > +                        &master_ctrl, 0);
> > +
> > +     if (!master_ctrl || !(master_ctrl->info.flags & UVC_CTRL_FLAG_GET_CUR))
> > +             return false;
> > +
> > +     ret = __uvc_ctrl_get(chain, master_ctrl, master_map, &val);
> > +     if (ret < 0 || val == mapping->master_manual)
> > +             return false;
> > +
> > +     return true;
> > +}
> > +
> >  static int __uvc_query_v4l2_ctrl(struct uvc_video_chain *chain,
> >       struct uvc_control *ctrl,
> >       struct uvc_control_mapping *mapping,
> >       struct v4l2_queryctrl *v4l2_ctrl)
> >  {
> > -     struct uvc_control_mapping *master_map = NULL;
> > -     struct uvc_control *master_ctrl = NULL;
> >       const struct uvc_menu_info *menu;
> >       unsigned int i;
> >
> > @@ -1104,18 +1127,8 @@ static int __uvc_query_v4l2_ctrl(struct uvc_video_chain *chain,
> >       if (!(ctrl->info.flags & UVC_CTRL_FLAG_SET_CUR))
> >               v4l2_ctrl->flags |= V4L2_CTRL_FLAG_READ_ONLY;
> >
> > -     if (mapping->master_id)
> > -             __uvc_find_control(ctrl->entity, mapping->master_id,
> > -                                &master_map, &master_ctrl, 0);
> > -     if (master_ctrl && (master_ctrl->info.flags & UVC_CTRL_FLAG_GET_CUR)) {
> > -             s32 val;
> > -             int ret = __uvc_ctrl_get(chain, master_ctrl, master_map, &val);
> > -             if (ret < 0)
> > -                     return ret;
>
> There's a small change in behaviour here, the driver used to return an
> error, now it will ignore it. Is it intentional ?

AFAIK The error did not follow the v4l2 spec. You shall always be able
to query a ctrl.

I will add it to the commit message to make it clear.

>
> > -
> > -             if (val != mapping->master_manual)
> > -                             v4l2_ctrl->flags |= V4L2_CTRL_FLAG_INACTIVE;
> > -     }
> > +     if (uvc_ctrl_is_inactive(chain, ctrl, mapping))
> > +             v4l2_ctrl->flags |= V4L2_CTRL_FLAG_INACTIVE;
> >
> >       if (!ctrl->cached) {
> >               int ret = uvc_ctrl_populate_cache(chain, ctrl);
> > @@ -1638,25 +1651,37 @@ static int uvc_ctrl_commit_entity(struct uvc_device *dev,
> >       return 0;
> >  }
> >
> > -static int uvc_ctrl_find_ctrlidx(struct uvc_entity *entity,
> > +static int uvc_ctrl_commit_error(struct uvc_video_chain *chain,
> > +                              struct uvc_entity *entity,
> >                                struct v4l2_ext_controls *ctrls,
> > -                              struct uvc_control *uvc_control)
> > +                              struct uvc_control *err_control,
> > +                              int ret)
> >  {
> >       struct uvc_control_mapping *mapping;
> >       struct uvc_control *ctrl_found;
> >       unsigned int i;
> >
> > -     if (!entity)
> > -             return ctrls->count;
> > +     if (!entity) {
> > +             ctrls->error_idx = ctrls->count;
> > +             return ret;
> > +     }
> >
> >       for (i = 0; i < ctrls->count; i++) {
> >               __uvc_find_control(entity, ctrls->controls[i].id, &mapping,
> >                                  &ctrl_found, 0);
> > -             if (uvc_control == ctrl_found)
> > -                     return i;
> > +             if (err_control == ctrl_found)
> > +                     break;
> >       }
> > +     ctrls->error_idx = i;
>
> I think this line should be moved after the next check.

Not really, if we cannot find a control, we cannot blame it on control 0 ;)

>
> > +
> > +     /* We could not find the control that failed. */
> > +     if (i == ctrls->count)
> > +             return ret;
> >
> > -     return ctrls->count;
> > +     if (uvc_ctrl_is_inactive(chain, err_control, mapping))
> > +             return -EACCES;
> > +
> > +     return ret;
> >  }
> >
> >  int __uvc_ctrl_commit(struct uvc_fh *handle, int rollback,
> > @@ -1679,8 +1704,8 @@ int __uvc_ctrl_commit(struct uvc_fh *handle, int rollback,
> >               uvc_ctrl_send_events(handle, ctrls->controls, ctrls->count);
> >  done:
> >       if (ret < 0 && ctrls)
> > -             ctrls->error_idx = uvc_ctrl_find_ctrlidx(entity, ctrls,
> > -                                                      err_ctrl);
> > +             ret = uvc_ctrl_commit_error(chain, entity, ctrls, err_ctrl,
> > +                                         ret);
> >       mutex_unlock(&chain->ctrl_mutex);
> >       return ret;
> >  }
>
> --
> Regards,
>
> Laurent Pinchart



-- 
Ricardo Ribalda