linux-kernel - Re: [PATCH v1 02/15] Documentation: ABI: add wideband filter type to sysfs-bus-iio

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Message-ID: <652a80dd-e951-4505-8e13-b5198c66c403@baylibre.com>
Date: Sun, 12 Jan 2025 11:39:54 -0600
From: David Lechner <dlechner@...libre.com>
To: 8601da92-1f08-40e3-9b39-f9b99dbc1507@...libre.com
Cc: Jonathan Santos <Jonathan.Santos@...log.com>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, lars@...afoo.de,
 Michael.Hennerich@...log.com, jic23@...nel.org, robh@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org, marcelo.schmitt1@...il.com
Subject: Re: [PATCH v1 02/15] Documentation: ABI: add wideband filter type to
 sysfs-bus-iio

On 1/11/25 4:50 PM, Jonathan Santos wrote:
> On 01/07, David Lechner wrote:
>> On 1/7/25 9:24 AM, Jonathan Santos wrote:
>>> The Wideband Low Ripple FIR filter is used for AD7768-1 Driver.
>>> Document wideband filter option into filter_type_avaialable
>>
>> s/avaialable/available/
>>
>>> attribute.
>>>
>>> Signed-off-by: Jonathan Santos <Jonathan.Santos@...log.com>
>>> ---
>>>  Documentation/ABI/testing/sysfs-bus-iio | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
>>> index f83bd6829285..c4c21a7bfba1 100644
>>> --- a/Documentation/ABI/testing/sysfs-bus-iio
>>> +++ b/Documentation/ABI/testing/sysfs-bus-iio
>>> @@ -2291,6 +2291,8 @@ Description:
>>>  		* "sinc3+pf2" - Sinc3 + device specific Post Filter 2.
>>>  		* "sinc3+pf3" - Sinc3 + device specific Post Filter 3.
>>>  		* "sinc3+pf4" - Sinc3 + device specific Post Filter 4.
>>> +		* "wideband" - FIR filter with wideband low ripple passband
>>
>> I think "fir" would be a more specific filter type name than "wideband". (i.e.
>> there are wikipedia pages for sinc and FIR filters, but not one for "wideband"
>> filters)
>>
> 
> Isn't "fir" a bit too generic for this case? Since Wideband here is a class of a FIR filter.
> Maybe something like "wideband-fir" or "fir-wideband" would work better?

For this particular chip, no, there is only one FIR filter option on the chip,
so having additional qualifiers doesn't really make a difference.

If we can find a chip that has more than one FIR filter option, then we could
use that to figure out what additional classifiers are might make sense.
"fir-wideband" would only be useful if the same chip also had a "fir-narrowband"
option. But we might find that instead the chip is actually "fir-type1"
"fir-type2" or something like that.

(FWIW, my signal processing textbook describes Type I, II, III, IV FIR filters
but doesn't say anything about "wideband" FIR filters.)

> 
>>> +		  and sharp transition band.
>>>  
>>>  What:		/sys/.../events/in_proximity_thresh_either_runningperiod
>>>  KernelVersion:	6.6
>>