linux-kernel - Re: [PATCH 2/2] iio: veml3235: fix scale to conform to ABI

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Message-ID: <b4b8ab5e-7b94-4919-98a4-1525be903954@gmail.com>
Date: Sun, 22 Dec 2024 15:43:16 +0200
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Javier Carrasco <javier.carrasco.cruz@...il.com>,
 Jonathan Cameron <jic23@...nel.org>, Lars-Peter Clausen <lars@...afoo.de>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH 2/2] iio: veml3235: fix scale to conform to ABI

On 20/12/2024 21:28, Javier Carrasco wrote:
> The current scale is not ABI-compliant as it is just the sensor gain
> instead of the value that acts as a multiplier to be applied to the raw
> value (there is no offset).
> 
> Use the iio-gts helpers to obtain the proper scale values according to
> the gain and integration time to match the resolution tables from the
> datasheet.
> 
> Fixes: c5a23f80c164 ("iio: light: add support for veml3235")
> Signed-off-by: Javier Carrasco <javier.carrasco.cruz@...il.com>
> ---

...

> +static const struct iio_itime_sel_mul veml3235_it_sel[] = {
> +	GAIN_SCALE_ITIME_US(50000, 0, 1),
> +	GAIN_SCALE_ITIME_US(100000, 1, 2),
> +	GAIN_SCALE_ITIME_US(200000, 2, 4),
> +	GAIN_SCALE_ITIME_US(400000, 3, 8),
> +	GAIN_SCALE_ITIME_US(800000, 4, 16),
>   };
>   
> -static const int veml3235_scale_vals[] = { 1, 2, 4, 8 };
> +/*
> + * The MSB (DG) doubles the value of the rest of the field, which leads to
> + * two possible combinations to obtain gain = 2 and gain = 4. The gain
> + * handlding can be simplified by restricting DG = 1 to the only gain that
> + * really requires it, gain = 8. Note that "X10" is a reserved value.

Just a question - do you ensure there is no "invalid" register values? I 
think Jonathan has prefered doing this by writing known initialization 
values at probe.

I *think* the GTS should survive cases where multiple bit patterns can 
be used to represent same gain/time - but I don't remember this for sure.

I didn't have the time to do a proper thorough review - sorry. Still, 
what I browsed quickly looked good :) Thanks!

Yours,
	-- Matti