Re: [PATCH v7 16/34] [media] add Omnivision OV5640 sensor driver

[Steve Longerbeam]

On 06/03/2017 02:57 PM, Sakari Ailus wrote:
> On Sat, Jun 03, 2017 at 09:51:39PM +0200, Pavel Machek wrote:
> > Hi!
> >
> > > > > > +	/* Auto/manual exposure */
> > > > > > +	ctrls->auto_exp = v4l2_ctrl_new_std_menu(hdl, ops,
> > > > > > +						 V4L2_CID_EXPOSURE_AUTO,
> > > > > > +						 V4L2_EXPOSURE_MANUAL, 0,
> > > > > > +						 V4L2_EXPOSURE_AUTO);
> > > > > > +	ctrls->exposure = v4l2_ctrl_new_std(hdl, ops,
> > > > > > +					    V4L2_CID_EXPOSURE_ABSOLUTE,
> > > > > > +					    0, 65535, 1, 0);
> > > > >
> > > > > Is exposure_absolute supposed to be in microseconds...?
> > > >
> > > > Yes.
> > >
> > > According to the docs V4L2_CID_EXPOSURE_ABSOLUTE is in 100 usec units.
> > >
> > >   OTOH V4L2_CID_EXPOSURE has no defined unit, so it's a better fit IMO.
> > > > Way more drivers appear to be using EXPOSURE than EXPOSURE_ABSOLUTE, too.
> > >
> > > Done, switched to V4L2_CID_EXPOSURE. It's true, this control is not
> > > taking 100 usec units, so unit-less is better.
> >
> > Thanks. If you know the units, it would be of course better to use
> > right units...
>
> Steve: what's the unit in this case? Is it lines or something else?

Yes, the register interface for exposure takes lines*16.

Maybe converting from seconds to lines is as simple as
framerate * height * seconds. But I'm not sure about that.

Steve

> Pavel: we do need to make sure the user space will be able to know the unit,
> too. It's rather a case with a number of controls: the unit is known but
> there's no API to convey it to the user.
>
> The exposure is a bit special, too: granularity matters a lot on small
> values. On most other controls it does not.