linux-kernel - Re: [PATCH 2/2] iio: light: Add support for Capella cm36686 and cm36672p sensors

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Message-ID: <20260207162643.5599a3ac@jic23-huawei>
Date: Sat, 7 Feb 2026 16:26:43 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Erikas Bitovtas <xerikasxx@...il.com>
Cc: David Lechner <dlechner@...libre.com>, Nuno Sá
 <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>, Rob Herring
 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Kevin Tsai <ktsai@...ellamicro.com>,
 linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, ~postmarketos/upstreaming@...ts.sr.ht,
 phone-devel@...r.kernel.org
Subject: Re: [PATCH 2/2] iio: light: Add support for Capella cm36686 and
 cm36672p sensors

On Wed, 4 Feb 2026 18:34:50 +0200
Erikas Bitovtas <xerikasxx@...il.com> wrote:

> > I assume you have the hardware and can do a test to confirm this. :-)  
> 
> I tested the formula used in Xiaomi's driver in the mainline kernel and
> compared it against the downstream kernel, and the lux readings match between
> them. Therefore, I suppose this solution could be good for now.
> Although my formula for calculating scale is wrong - it should be inverse
> proportionate to integration time. So:
> 80ms -> 1.28
> 160ms -> 0.64 (what Xiaomi uses)
> 320ms -> 0.32
> 640ms -> 0.16
> This can be achieved by multiplying als_trans_ratio by integration time used in
> Xiaomi's driver, and then dividing by integration time we have set up at the
> given moment.
> For example, suppose we set our int time in mainline to 80ms
> 16 (als_trans_ration) * 16 (160ms / 10000) = 256
> 256 / 8 (80ms / 10000) = 32
> Starting here, we calculate based on how Xiaomi calculates scale for their values:
> 32 * 40000 = 1280000
> val = 1280000 / 1000000 = 1
> val2 = 1280000 % 1000000 = 280000
> And that leaves us with scale of 1.280000.
> Of course, comments on how we came to this value would be included as well.

Only think I'd add to this is that if we have numbers for
a sensor in a specific device, it's common for that devices
packaging to attenuate the measured light level a little.

For that reason we do sometimes have a tweak factor in DT.

Jonathan