Work on iio: stating: frequency: ad9832

[Marcelo Schmitt]

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).
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.
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?
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?

I'm sending a patchset with some things I've already done.

Is there something else that could be done in this device driver?
Please, tell if I've forgotten something.

Any advice is welcome.
Thanks,

Marcelo