linux-kernel - Re: [PATCH 5/6] iio: adc: ad7124: add filter support

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Message-ID: <20250910172907.5e6cbc6c@jic23-huawei>
Date: Wed, 10 Sep 2025 17:29:07 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: David Lechner <dlechner@...libre.com>
Cc: Michael Hennerich <Michael.Hennerich@...log.com>, Nuno Sá
 <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>,
 linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] iio: adc: ad7124: add filter support

On Sun, 7 Sep 2025 11:22:14 +0100
Jonathan Cameron <jic23@...nel.org> wrote:

> On Fri, 05 Sep 2025 13:12:00 -0500
> David Lechner <dlechner@...libre.com> wrote:
> 
> > Add support to the ad7124 driver for selecting the filter type.
> > 
> > The filter type has an influence on the effective sampling frequency of
> > each channel. For sinc3+pf{1,2,3,4}, the sampling frequency is fixed.
> > For sinc{3,4} (without post filter), there is a factor of 3 or 4
> > depending on the filter type. For the extra +sinc1, there is an extra
> > averaging factor that depends on the power mode.
> > 
> > In order to select the closest sampling frequency for each filter type,
> > we keep a copy of the requested sampling frequency. This way, if the
> > user sets the sampling frequency first and then selects the filter type,
> > the sampling frequency will still be as close as possible to the
> > requested value.
> > 
> > Since we always either have the SINGLE_CYCLE bit set or have more than
> > one channel enabled, the sampling frequency is always using the
> > "zero-latency" calculation from the data sheet. This is only documented
> > for the basic sinc{3,4} filters, so the other filter types had to be
> > inferred and confirmed through testing.
> > 
> > Since the flat filter type list consists of multiple register fields,
> > the struct ad7124_channel_config::filter_type field is changed to the
> > enum ad7124_filter_type type to avoid nested switch statements in a
> > lot of places.
> > 
> > Signed-off-by: David Lechner <dlechner@...libre.com>  
> 
> One really trivial comment inline.  Not worth a v2 for just that.
> However, this is complex enough code I'd like to keep this on list anyway
> for a little longer to see if anyone else has review comments.
> 
> Jonathan
Hi David,

Given your self review of the fix, I am assuming you will do a new
version of that and these.  Which mostly means I'll mark them as waiting
for changes in patchwork and forget about them till I see the new version :)

Thanks,

Jonathan