Re: [PATCH 1/1] mt9v032: Provide pixel rate control

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Hi Laurent,

On Fri, Mar 16, 2012 at 01:31:39PM +0100, Laurent Pinchart wrote:
> On Friday 16 March 2012 14:12:11 Sakari Ailus wrote:
> > On Fri, Mar 16, 2012 at 12:58:30PM +0100, Laurent Pinchart wrote:
> > > On Thursday 15 March 2012 23:01:39 Sakari Ailus wrote:
> > > > Provide pixel rate control calculated from external clock and horizontal
> > > > binning factor.
> > > > 
> > > > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxx>
> > > > ---
> > > > 
> > > >  drivers/media/video/mt9v032.c |   35  ++++++++++++++++++++++++++++++++-
> > > >  1 files changed, 34 insertions(+), 1 deletions(-)
> > > > 
> > > > diff --git a/drivers/media/video/mt9v032.c
> > > > b/drivers/media/video/mt9v032.c
> > > > index 75e253a..e530e8d 100644
> > > > --- a/drivers/media/video/mt9v032.c
> > > > +++ b/drivers/media/video/mt9v032.c
> 
> [snip]
> 
> > > > +static void mt9v032_configure_pixel_rate(struct v4l2_subdev *subdev,
> > > > +					 unsigned int hratio)
> > > > +{
> > > > +	struct i2c_client *client = v4l2_get_subdevdata(subdev);
> > > > +	struct mt9v032 *mt9v032 = to_mt9v032(subdev);
> > > > +	struct v4l2_ext_controls ctrls;
> > > > +	struct v4l2_ext_control ctrl;
> > > > +
> > > > +	memset(&ctrls, 0, sizeof(ctrls));
> > > > +	memset(&ctrl, 0, sizeof(ctrl));
> > > > +
> > > > +	ctrls.count = 1;
> > > > +	ctrls.controls = &ctrl;
> > > > +
> > > > +	ctrl.id = V4L2_CID_PIXEL_RATE;
> > > > +	ctrl.value64 = EXT_CLK / hratio;
> > > > +
> > > > +	if (v4l2_s_ext_ctrls(mt9v032->pixel_rate->ctrl_handler, &ctrls) < 0)
> > > > +		dev_warn(&client->dev, "bug: failed to set pixel rate\n");
> > > 
> > > What about just calling v4l2_ctrl_s_ctrl() ?
> > 
> > It's a 64-bit integer control, so it has to be set using v4l2_s_ext_ctrls().
> 
> What about extending v4l2_ctrl_s_ctrl() to support 64-bit integer controls 
> then ?

The second argument to that function is struct v4l2_control:

struct v4l2_control {
        __u32                id;
        __s32                value;
};

So there's no chance to extend it. This must also be the reason why 64-bit
controls require using extended controls.

What we could do is to introduce v4l2_s_ext_ctrl without the "s" in the end
to just set one extended control. I think that would be a reasonable
approach, as it seems we need the functionality in multiple places.

Regards,

-- 
Sakari Ailus
e-mail: sakari.ailus@xxxxxx	jabber/XMPP/Gmail: sailus@xxxxxxxxxxxxxx
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