linux-kernel - Re: [PATCH v4 7/8] iio: light: ROHM BU27034 Ambient Light Sensor

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Message-ID: <61169e7e-b839-eb06-046f-e41bd3eabcec@gmail.com>
Date:   Fri, 17 Mar 2023 16:48:41 +0200
From:   Matti Vaittinen <mazziesaccount@...il.com>
To:     Matti Vaittinen <matti.vaittinen@...rohmeurope.com>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Paul Gazzillo <paul@...zz.com>,
        Zhigang Shi <Zhigang.Shi@...eon.com>,
        Shreeya Patel <shreeya.patel@...labora.com>,
        Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org
Subject: Re: [PATCH v4 7/8] iio: light: ROHM BU27034 Ambient Light Sensor

On 3/17/23 16:44, Matti Vaittinen wrote:
> ROHM BU27034 is an ambient light sensor with 3 channels and 3 photo diodes
> capable of detecting a very wide range of illuminance. Typical application
> is adjusting LCD and backlight power of TVs and mobile phones.
> 
> Add initial  support for the ROHM BU27034 ambient light sensor.
> 
> NOTE:
> 	- Driver exposes 4 channels. One IIO_LIGHT channel providing the
> 	  calculated lux values based on measured data from diodes #0 and
> 	  #1. In addition, 3 IIO_INTENSITY channels are emitting the raw
> 	  register data from all diodes for more intense user-space
> 	  computations.
> 	- Sensor has GAIN values that can be adjusted from 1x to 4096x.
> 	- Sensor has adjustible measurement times of 5, 55, 100, 200 and
> 	  400 mS. Driver does not support 5 mS which has special
> 	  limitations.
> 	- Driver exposes standard 'scale' adjustment which is
> 	  implemented by:
> 		1) Trying to adjust only the GAIN
> 		2) If GAIN adjustment alone can't provide requested
> 		   scale, adjusting both the time and the gain is
> 		   attempted.
> 	- Driver exposes writable INT_TIME property that can be used
> 	  for adjusting the measurement time. Time adjustment will also
> 	  cause the driver to try to adjust the GAIN so that the
> 	  overall scale is kept as close to the original as possible.
> 
> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
> 
> ---
> Changes
> v3 => v4:
> - use min_t() for division by zero check
> - adapt to new GTS helper header location
> - calculate luxes not milli luxes
> - drop scale for PROCESSED channel
> - comment improvements
> - do not allow changing gain (scale) for channel 2.
>     - 'tie' channel 2 scale to channel 0 scale
>       This is because channel 0 and channel 2 GAIN settings share part of
>       the bits in the register. This means that setting one will also
>       impact the other. The v3 of the patches attempted to work-around
>       this by only disallowing the channel 2 gain setting to set the bits
>       which were shared with channel 0 gain. This does not work because
>       setting channel 0 gain (which was allowed to set also the shared
>       bits) could result unsupported bit combinations for channel 2 gain.
>       Thus it is safest to always set also the channel 2 gain to same
>       value as channel 0 gain.
> - Use the correct integration time (55 mS) in the gain table as the
>    calcuations can be done based on the time multiplier.
> - styling
> 

And right after sending out this version I realized I forgot to run 
spell-checker for the comments. I will do that for v5 - please bear with me.

Yours,
	-- Matti

-- 
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

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