linux-kernel - Re: Work on iio: stating: frequency: ad9832

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Message-ID: <CA+U=DsrFdfaQQkzFiEuA5yn=Vu0RGVirm+nBuMEaioZOrEhVzg@mail.gmail.com>
Date:   Tue, 2 Apr 2019 10:12:47 +0300
From:   Alexandru Ardelean <ardeleanalex@...il.com>
To:     Jonathan Cameron <jonathan.cameron@...wei.com>
Cc:     Marcelo Schmitt <marcelo.schmitt1@...il.com>,
        linux-iio@...r.kernel.org, devel@...verdev.osuosl.org,
        LKML <linux-kernel@...r.kernel.org>, kernel-usp@...glegroups.com
Subject: Re: Work on iio: stating: frequency: ad9832

On Mon, Apr 1, 2019 at 7:13 PM Jonathan Cameron
<jonathan.cameron@...wei.com> wrote:
>
> On Mon, 1 Apr 2019 11:25:29 -0300
> Marcelo Schmitt <marcelo.schmitt1@...il.com> 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!)
>

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.

> > 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.
> >
> > 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
>
>