linux-kernel - Re: [PATCH 01/15] iio: adc: ad4030: Fix _scale for when oversampling is enabled

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <97f20435-e4b9-49c5-ab02-b67a8112f0ee@baylibre.com>
Date: Sat, 30 Aug 2025 13:48:03 -0500
From: David Lechner <dlechner@...libre.com>
To: Jonathan Cameron <jic23@...nel.org>,
 Marcelo Schmitt <marcelo.schmitt@...log.com>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, devicetree@...r.kernel.org,
 linux-spi@...r.kernel.org, Michael.Hennerich@...log.com, nuno.sa@...log.com,
 eblanc@...libre.com, andy@...nel.org, corbet@....net, robh@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org, broonie@...nel.org,
 Jonathan.Cameron@...wei.com, andriy.shevchenko@...ux.intel.com,
 ahaslam@...libre.com, marcelo.schmitt1@...il.com
Subject: Re: [PATCH 01/15] iio: adc: ad4030: Fix _scale for when oversampling
 is enabled

On 8/30/25 1:43 PM, Jonathan Cameron wrote:
> On Fri, 29 Aug 2025 21:40:24 -0300
> Marcelo Schmitt <marcelo.schmitt@...log.com> wrote:
> 
>> Previously, the AD4030 driver was using the number of scan realbits for the
>> voltage channel to derive the scale to millivolts. Though, when sample
>> averaging is enabled (oversampling_ratio > 1), the number of scan realbits
>> for the channel is set to 30 and doesn't match the amount of conversion
>> precision bits. Due to that, the calculated channel scale did not correctly
>> scale raw sample data to millivolt units in those cases. Use chip specific
>> precision bits to derive the correct channel _scale on every and all
>> channel configuration.
>>
>> Fixes: dc78e71d7c15 ("iio: adc: ad4030: remove some duplicate code")
>> Signed-off-by: Marcelo Schmitt <marcelo.schmitt@...log.com>
> 
> Hi Marcelo
> 
> I was assuming that when this said 'averaging' it actually meant
> summing (there is a note about using the upper precision bits to get the same
> scaling which is what we'd expect it were simply summing over X samples).
> 
> So given that we don't divide back down to get the original scaling I'm
> not following how this works.

I had the same feeling. I have some hardware I can test later this week.