linux-kernel - Re: [PATCH v6 7/8] iio: dac: ad3552r: add high-speed platform driver

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Message-ID: <781cf5fa075e13260e1b20f5acadb70bd8107cd0.camel@gmail.com>
Date: Tue, 15 Oct 2024 17:00:10 +0200
From: Nuno Sá <noname.nuno@...il.com>
To: David Lechner <dlechner@...libre.com>, Angelo Dureghello
 <adureghello@...libre.com>, Nuno Sá
 <nuno.sa@...log.com>,  Lars-Peter Clausen <lars@...afoo.de>, Michael
 Hennerich <Michael.Hennerich@...log.com>,  Jonathan Cameron
 <jic23@...nel.org>, Rob Herring <robh@...nel.org>, Krzysztof Kozlowski
 <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, Olivier Moysan
 <olivier.moysan@...s.st.com>
Cc: linux-iio@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v6 7/8] iio: dac: ad3552r: add high-speed platform driver

On Tue, 2024-10-15 at 09:38 -0500, David Lechner wrote:
> On 10/15/24 1:37 AM, Nuno Sá wrote:
> > On Mon, 2024-10-14 at 16:15 -0500, David Lechner wrote:
> > > On 10/14/24 5:08 AM, Angelo Dureghello wrote:
> > > > From: Angelo Dureghello <adureghello@...libre.com>
> > > > 
> > > > Add High Speed ad3552r platform driver.
> > > > 
> > > 
> > > ...
> > > 
> > > > +static int ad3552r_hs_read_raw(struct iio_dev *indio_dev,
> > > > +			       struct iio_chan_spec const *chan,
> > > > +			       int *val, int *val2, long mask)
> > > > +{
> > > > +	struct ad3552r_hs_state *st = iio_priv(indio_dev);
> > > > +	int ret;
> > > > +
> > > > +	switch (mask) {
> > > > +	case IIO_CHAN_INFO_SAMP_FREQ: {
> > > > +		int sclk;
> > > > +
> > > > +		ret = iio_backend_read_raw(st->back, chan, &sclk, 0,
> > > > +					   IIO_CHAN_INFO_FREQUENCY);
> > > 
> > > FWIW, this still seems like an odd way to get the stream mode SCLK
> > > rate from the backend to me. How does the backend know that we want
> > > the stream mode clock rate and not some other frequency value? 
> > 
> > In this case the backend has a dedicated compatible so sky is the limit :). But
> > yeah,
> > I'm also not extremely happy with IIO_CHAN_INFO_FREQUENCY. But what do you have
> > in
> > mind? Using the sampling frequency INFO or a dedicated OP?
> > 
> 
> It think it would be most straightforward to have something
> like a iio_backend_get_data_stream_clock_rate() callback since
> that is what we are getting.

Hmmm, what about exporting an actual clock? Maybe it's overkill but from a
correctness point of view, seems what we should actually do :)

> 
> Re: the other recent discussions about getting too many
> callbacks. Instead of a dedicated function like this, we
> could make a set of generic functions:
> 
> iio_backend_{g,s}et_property_{s,u}(8, 16, 32, 64}()
> 

Hmm interesting approach. I don't dislike it. Kind of a generic getter/setter thingy.
We could then still have optional inline helpers that would call the generic
functions with the proper enum value.

> that take an enum parameter for the property. This way,
> for each new property, we just have to add an enum member
> instead of creating a get/set callback pair.
> 
> Unrelated to this particular case, but taking the idea even
> farther, we could also do the same with enable/disable
> functions. We talked before about cutting the number of
> callbacks in half by using a bool parameter instead of
> separate enable/disable callbacks. But we could cut it down
> even more by having an enum parameter for the thing we are
> enabling/disabling.

If we don't get too strict about types it could even fall into the above u8 category.

Instead of lot of new simple ops we just grow an enum.

- Nuno Sá