linux-kernel - Re: [PATCH 6/6] iio: mcp9600: Add support for IIR filter

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Message-ID: <2025081910-shiny-trout-a937ef@boujee-and-buff>
Date: Tue, 19 Aug 2025 10:32:15 -0400
From: Ben Collins <ben.collins@...ux.dev>
To: David Lechner <dlechner@...libre.com>
Cc: Jonathan Cameron <jic23@...nel.org>, 
	Nuno Sá <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>, linux-iio@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] iio: mcp9600: Add support for IIR filter

On Tue, Aug 19, 2025 at 09:15:23AM -0500, David Lechner wrote:
> On 8/19/25 9:11 AM, Ben Collins wrote:
> > On Tue, Aug 19, 2025 at 09:05:39AM -0500, David Lechner wrote:
> >> On 8/18/25 1:32 PM, Ben Collins wrote:
> >>> From: Ben Collins <bcollins@...ter.com>
> >>>
> >>> MCP9600 supports an IIR filter with 7 levels. Add IIR attribute
> >>> to allow get/set of this value.
> >>>
> >>> Use a filter_type[none, ema] for enabling the IIR filter.
> >>>
> >>> Signed-off-by: Ben Collins <bcollins@...ter.com>
> >>> ---
> >>> +		if (data->filter_level == 0)
> >>> +			return -EINVAL;
> >>
> >> To implement Jonathan's request from v5, drop this error return.
> >> We'll also need a separate bool data->is_filter_enabled field so
> >> that we can keep the last set filter_level even when the filter
> >> is disabled. (i.e. data->filter_level is never == 0).
> >>
> >> This way, if you set the filter level, you can enable and disable
> >> the filter via filter_type and still have the same filter level.
> >>
> > 
> > Thanks, David. This is exactly what I've implemented, plus the
> > filter_enable attribute.
> > 
> > Adding the ABI doc updates as well.
> > 
> 
> 
> Don't add the filter_enable attribute. The filter_type attribute
> already does the job.

That doesn't solve the problem at hand. An example:

- Driver has 3 possible filter_type's, plus "none"
- User cats filter_type_available and sees [none, sinc4, sinc5, sinc5+avg]
- User cats filter_type and sees "none"
- User cats frequency_available: What do they see?
- User cats frequency: What do they see?

Without filter_enable, [none, ema] driver works just fine. But the
above driver does not.

-- 
 Ben Collins
 https://libjwt.io
 https://github.com/benmcollins
 --
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