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

[Ricardo Ribalda Delgado]

Hi Laurent

On Thu, Jun 10, 2021 at 8:43 PM Ricardo Ribalda <ribalda@xxxxxxxxxxxx> wrote:
>
> 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.

In my hardware after reverting the patch I am still passing v4l2-compliance.

The benefits of this patch are:

1) We return -EACCESS even if the hardware mistakenly returns a different error
2) query_ctrl returns a value for hardware errors.

Hans can you comment on this? Shall we remove the patch ?

Thanks!

>
> >
> > > 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



-- 
Ricardo Ribalda