linux-kernel - Re: [PATCH v2] media: uvcvideo: Fix handling on Bitmask controls

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Date:   Fri, 25 Mar 2022 00:18:51 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Ricardo Ribalda <ribalda@...omium.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Hans Verkuil <hverkuil-cisco@...all.nl>
Subject: Re: [PATCH v2] media: uvcvideo: Fix handling on Bitmask controls

Hi Ricardo,

On Thu, Mar 24, 2022 at 10:56:37PM +0100, Ricardo Ribalda wrote:
> On Thu, 24 Mar 2022 at 21:25, Laurent Pinchart wrote:
> > On Tue, Feb 15, 2022 at 06:42:28PM +0000, Ricardo Ribalda wrote:
> > > Minimum and step values for V4L2_CTRL_TYPE_BITMASK controls should be 0.
> > > There is no need to query the camera firmware about this and maybe get
> > > invalid results.
> > >
> > > Also value should be clamped to the min/max value advertised by the
> > > hardware.
> > >
> > > Fixes v4l2-compliane:
> > > Control ioctls (Input 0):
> > >                 fail: v4l2-test-controls.cpp(97): minimum must be 0 for a bitmask control
> > >       test VIDIOC_QUERY_EXT_CTRL/QUERYMENU: FAIL
> >
> > What bitmask control do you have ? The driver has no standard control
> > that use the V4L2_CTRL_TYPE_BITMASK type.
> >
> > UVC doesn't formally define bitmask control type
> > (UVC_CTRL_DATA_TYPE_BITMASK). In UVC 1.1 only the UVC_CT_AE_MODE_CONTROL
> > control has a bitmap type, and only one bit can be set at a type. It
> > thus maps to a V4L2 menu control.
> >
> > In UVC 1.5 there are other controls documented as bitmap controls,
> > which could map to the V4L2 bitmask control type. Those don't support
> > GET_MIN and GET_MAX, but use GET_RES to report the list of bits that can
> > be set. This should be mapped to the V4L2 control maximum value, which
> > isn't handled by this patch. The last hunk is also incorrect, as it
> > clamps the value to what is reported by GET_MIN and GET_MAX, instead of
> > [0, GET_RES], but more than that, it should not just clamp the value,
> > but check that all bits are valid.
> 
> I am particularly looking at bmAutoControls from CT_REGION_OF_INTEREST_CONTROL
> 
> The doc says that:
> """
>  To detect if a device supports a particular Auto Control, use GET_MAX
> which returns a mask indicating all supported Auto Controls.
> """

But if you look at CT_AE_MODE_CONTROL,

"A GET_RES request issued to this control will return a bitmap of the
modes supported by this control. A valid request to this control would
have only one bit set (a single mode selected)."

GET_MIN and GET_MAX are not listed as supported.

Maybe we need two types of UVC bitmap controls ? :-(

> GET_RES does not seem to return the max_value accoring to the uvc
> class spec, but I will try to validate tomorrow with real hardware,
> maybe we are lucky.
> 
> And I definitely have to fix the clamp, thanks for pointing that out :)
> 
> > > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > > ---
> > >  drivers/media/usb/uvc/uvc_ctrl.c | 7 +++++--
> > >  1 file changed, 5 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> > > index b4f6edf968bc0..d8b9ab5b7fb85 100644
> > > --- a/drivers/media/usb/uvc/uvc_ctrl.c
> > > +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> > > @@ -1156,7 +1156,8 @@ static int __uvc_query_v4l2_ctrl(struct uvc_video_chain *chain,
> > >               break;
> > >       }
> > >
> > > -     if (ctrl->info.flags & UVC_CTRL_FLAG_GET_MIN)
> > > +     if (ctrl->info.flags & UVC_CTRL_FLAG_GET_MIN &&
> > > +         mapping->v4l2_type != V4L2_CTRL_TYPE_BITMASK)
> > >               v4l2_ctrl->minimum = mapping->get(mapping, UVC_GET_MIN,
> > >                                    uvc_ctrl_data(ctrl, UVC_CTRL_DATA_MIN));
> > >
> > > @@ -1164,7 +1165,8 @@ static int __uvc_query_v4l2_ctrl(struct uvc_video_chain *chain,
> > >               v4l2_ctrl->maximum = mapping->get(mapping, UVC_GET_MAX,
> > >                                    uvc_ctrl_data(ctrl, UVC_CTRL_DATA_MAX));
> > >
> > > -     if (ctrl->info.flags & UVC_CTRL_FLAG_GET_RES)
> > > +     if (ctrl->info.flags & UVC_CTRL_FLAG_GET_RES &&
> > > +         mapping->v4l2_type != V4L2_CTRL_TYPE_BITMASK)
> > >               v4l2_ctrl->step = mapping->get(mapping, UVC_GET_RES,
> > >                                 uvc_ctrl_data(ctrl, UVC_CTRL_DATA_RES));
> > >
> > > @@ -1721,6 +1723,7 @@ int uvc_ctrl_set(struct uvc_fh *handle,
> > >       /* Clamp out of range values. */
> > >       switch (mapping->v4l2_type) {
> > >       case V4L2_CTRL_TYPE_INTEGER:
> > > +     case V4L2_CTRL_TYPE_BITMASK:
> > >               if (!ctrl->cached) {
> > >                       ret = uvc_ctrl_populate_cache(chain, ctrl);
> > >                       if (ret < 0)

-- 
Regards,

Laurent Pinchart