linux-kernel - Re: [PATCH 3/5] iio: adc: ad7606: add offset and phase calibration support

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Message-ID: <b4598086-e188-4dca-b060-0dd82fc79c02@baylibre.com>
Date: Wed, 30 Apr 2025 13:33:35 -0500
From: David Lechner <dlechner@...libre.com>
To: Nuno Sá <noname.nuno@...il.com>,
 Angelo Dureghello <adureghello@...libre.com>,
 Jonathan Cameron <jic23@...nel.org>, Nuno Sá
 <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>,
 Lars-Peter Clausen <lars@...afoo.de>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
 devicetree@...r.kernel.org
Subject: Re: [PATCH 3/5] iio: adc: ad7606: add offset and phase calibration
 support

On 4/30/25 11:14 AM, David Lechner wrote:
> On 4/30/25 10:36 AM, Nuno Sá wrote:
>> On Tue, 2025-04-29 at 15:06 +0200, Angelo Dureghello wrote:
>>> From: Angelo Dureghello <adureghello@...libre.com>
>>>
>>>

...

>>> +
>>> +	val += start_val;
>>
>> Shouldn't this be val -= start_val?
>>
>> I also don't think we have any strict rules in the ABI for units for these kind
>> of interfaces so using "raw" values is easier. But FWIW, I think we could have
>> this in mv (would naturally depend on scale) 
>>
>> - Nuno Sá
>>
> 
> From testing, it seems to be working as expected for me, so I think this is
> correct. The register value is not signed. 0x80 is no offset.
> 

Heh, you are actually quite right. Even though it working correctly, it is
because the value that gets written to the register is val & 0xFF, so adding
or subtracting here basically has the same effect. But subtracting is the more
logical way to do it. (I tested it that way too just to be 100% sure.)