Re: Work on iio: stating: frequency: ad9832

[Marcelo Schmitt]

On 04/02, Alexandru Ardelean wrote:
> On Mon, Apr 1, 2019 at 7:13 PM Jonathan Cameron
> <jonathan.cameron@xxxxxxxxxx> wrote:
> >
> > On Mon, 1 Apr 2019 11:25:29 -0300
> > Marcelo Schmitt <marcelo.schmitt1@xxxxxxxxx> wrote:
> >
> > > Hello,
> > >
> > > I was looking for some work on staging: iio: ad9832 and made some
> > > observations while reading the driver.
> > >
> > > Apparently it had no devicetree documentation so I tried to elaborate
> > > one.
> > > It uses a platform_data variable to load external clock
> > > frequency (I tried to make it use linux's clock framework).
> > Good.
> >
> > > Some device attributes don't seem to be standardized on
> > > Documentation/ABI/testing/sysfs-bus-iio and there's no specific ABI
> > > for ad9832 nearby nor at staging/iio/Documentation. So maybe those
> > > missing ABI could be documented.
> > Beware. It's an old driver, so it may be that we actually want to change
> > it's ABI rather than documenting what is there (I have haven't looked!)
> >

OK, I'll take more time studying the device's datasheet to better     
understand the current ABI.

> 
> This one can actually be coupled a bit with the AD9834 driver.
> There's been some work on trying to move that one out of staging as well.
> 
> You can take a look at the patches sent for that driver.
> They should be find-able on patchwork
> https://patchwork.kernel.org/project/linux-iio/list/?series=&submitter=&state=*&q=ad9834&archive=both&delegate=
> 
> There are ideas worth borrowing from there.
> 
> The issue with the AD9834 [if i recall correctly] is that it doesn't
> quite fit the classical IIO channel model.
> Meaning, you can only activate the output of one channel at one moment
> in time, and not both.

OK, I'll have a look at it.

> 
> > > The device has to set some internal registers to operate correctly,
> > > AD9832_FREQXHM and AD9832_PHASEXH, would it be feasible to set iio
> > > chanels for this?
> >
> > What are they?  If they correspond to output channels in some sensible
> > way then maybe...
> >
> > > I couldn't understand why checkpatch.pl gave errors on IIO_DEV_ATTR_*
> > > macros. To me they seem to have no problem.
> > > Also it has that platform_data to be moved to include/linux/iio. Is
> > > there any special reason for it not being there already? Which are
> > > the criterions a platform_data need to satisfy to be put there?
> > A driver moving out of staging shouldn't have platform data. It needs
> > to be converted over to more modern mechanisms.   We don't have a problem
> > supporting platform data for devices that have old school device files
> > already in tree, but that shouldn't be the case for a driver in staging.
> >
> > Hence we can clean it up and move forward with just DT bindings.
> > >

Understood. Thanks for the explanation.

> > > I'm sending a patchset with some things I've already done.
> > Cool. I'll look at those later in the week if no one beats me to them.
> >
> > >
> > > Is there something else that could be done in this device driver?
> > > Please, tell if I've forgotten something.
> >
> > I'll take a look, but it may be a little while before I do.
> > Hopefully someone else gets there first!
> >
> > Jonathan
> >
> > >
> > > Any advice is welcome.
> > > Thanks,
> > >
> > > Marcelo
> >
> >

Thanks for the pieces of advice.

Marcelo