linux-kernel - Re: [RFC 3/5] media: v4l2-ctrls: Add support for V4L2_CID

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Date:   Thu, 15 Aug 2019 16:03:10 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Jacopo Mondi <jacopo@...ndi.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        "open list:MEDIA INPUT INFRASTRUCTURE (V4L/DVB)" 
        <linux-media@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 3/5] media: v4l2-ctrls: Add support for V4L2_CID_LOCATION

On Thu, Aug 15, 2019 at 03:02:45PM +0200, Jacopo Mondi wrote:
> Hi Laurent,
> 
> On Thu, Aug 15, 2019 at 01:53:53AM +0300, Laurent Pinchart wrote:
> > Hi Jacopo,
> >
> > Thank you for the patch.
> >
> > On Wed, Aug 14, 2019 at 10:28:13PM +0200, Jacopo Mondi wrote:
> > > Add support for the newly defined V4L2_CID_LOCATION read-only control
> > > used to report the camera device mounting position.
> > >
> > > Signed-off-by: Jacopo Mondi <jacopo@...ndi.org>
> > > ---
> > >  drivers/media/v4l2-core/v4l2-ctrls.c | 7 +++++++
> > >  include/uapi/linux/v4l2-controls.h   | 4 ++++
> > >  2 files changed, 11 insertions(+)
> > >
> > > diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
> > > index 7d3a33258748..8ab0857df59a 100644
> > > --- a/drivers/media/v4l2-core/v4l2-ctrls.c
> > > +++ b/drivers/media/v4l2-core/v4l2-ctrls.c
> > > @@ -943,6 +943,7 @@ const char *v4l2_ctrl_get_name(u32 id)
> > >  	case V4L2_CID_AUTO_FOCUS_RANGE:		return "Auto Focus, Range";
> > >  	case V4L2_CID_PAN_SPEED:		return "Pan, Speed";
> > >  	case V4L2_CID_TILT_SPEED:		return "Tilt, Speed";
> > > +	case V4L2_CID_LOCATION:			return "Location";
> >
> > Depending on what we decide to name the control (see review of 2/5), you
> > should adjust the description accordingly.
> >
> > >
> > >  	/* FM Radio Modulator controls */
> > >  	/* Keep the order of the 'case's the same as in v4l2-controls.h! */
> > > @@ -1300,6 +1301,12 @@ void v4l2_ctrl_fill(u32 id, const char **name, enum v4l2_ctrl_type *type,
> > >  		break;
> > >  	case V4L2_CID_MPEG_VIDEO_FWHT_PARAMS:
> > >  		*type = V4L2_CTRL_TYPE_FWHT_PARAMS;
> > > +	case V4L2_CID_LOCATION:
> > > +		*type = V4L2_CTRL_TYPE_INTEGER;
> > > +		*flags |= V4L2_CTRL_FLAG_READ_ONLY;
> > > +		*min = V4L2_LOCATION_FRONT;
> > > +		*max = V4L2_LOCATION_BACK;
> >
> > I don't think the control should have a min and a max different than the
> > current value, as it's a fully static control. I'd drop those two lines
> > here, and drivers will have to set value = min = max = V4L2_LOCATION_xxx
> > when creating the control. That why you should be able to collapse this
> > with V4L2_CID_MIN_BUFFERS_FOR_OUTPUT.
> >
> 
> Ah, I thought min/max should report the actual control values limits.
> Anyway, if we move this to be an integer menu control with an helper
> to parse the DT property and register the control on behalf of
> drivers, this will change.
> 
> > > +		*step = 1;
> > >  		break;
> > >  	default:
> > >  		*type = V4L2_CTRL_TYPE_INTEGER;
> > > diff --git a/include/uapi/linux/v4l2-controls.h b/include/uapi/linux/v4l2-controls.h
> > > index 37807f23231e..5c4c7b245921 100644
> > > --- a/include/uapi/linux/v4l2-controls.h
> > > +++ b/include/uapi/linux/v4l2-controls.h
> > > @@ -889,6 +889,10 @@ enum v4l2_auto_focus_range {
> > >  #define V4L2_CID_PAN_SPEED			(V4L2_CID_CAMERA_CLASS_BASE+32)
> > >  #define V4L2_CID_TILT_SPEED			(V4L2_CID_CAMERA_CLASS_BASE+33)
> > >
> > > +#define V4L2_CID_LOCATION			(V4L2_CID_CAMERA_CLASS_BASE+34)
> > > +#define V4L2_LOCATION_FRONT			(0 << 0)
> > > +#define V4L2_LOCATION_BACK			(1 << 0)
> >
> > Why not just 0 and 1 ?
> 
> Or why not BIT().

No, BIT(0) == (0 << 0) but BIT(1) != (1 << 0).

> I saw that the (1 << x) style is the mostly used one in this header
> file when defining macros like this one so I went for consistency with
> the existing code.

That's when you need a bitmask, which isn't the case here.

> > > +
> > >  /* FM Modulator class control IDs */
> > >
> > >  #define V4L2_CID_FM_TX_CLASS_BASE		(V4L2_CTRL_CLASS_FM_TX | 0x900)

-- 
Regards,

Laurent Pinchart