linux-kernel - Re: [PATCH 3/3] iio: light: Add support for ltrf216a sensor

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Date:   Sun, 27 Mar 2022 23:59:28 -0400
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     Shreeya Patel <shreeya.patel@...labora.com>
Cc:     jic23@...nel.org, lars@...afoo.de, robh+dt@...nel.org,
        Zhigang.Shi@...eon.com, linux-iio@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com, alvaro.soliverez@...labora.com
Subject: Re: [PATCH 3/3] iio: light: Add support for ltrf216a sensor

Shreeya Patel <shreeya.patel@...labora.com> writes:

> From: Zhigang Shi <Zhigang.Shi@...eon.com>
>
> Add initial support for ltrf216a ambient light sensor.
>
> Datasheet :-
> https://gitlab.steamos.cloud/shreeya/iio/-/blob/main/LTR-F216A-QT.pdf
> +	struct ltrf216a_data *data = iio_priv(indio_dev);
> +
> +	ret = i2c_smbus_write_byte_data(data->client, LTRF216A_MAIN_CTRL, 0);
> +	if (ret < 0)
> +		dev_err(&data->client->dev, "Error writing LTRF216A_MAIN_CTRL\n");
> +
> +	return ret;
> +}
> +
> +static int ltrf216a_set_it_time(struct ltrf216a_data *data, int itime)

ltrf216a_set_int_time instad of it_time?  although, ltr501 also uses
"it" instead of "int" on the function name..

> +
> +static int ltrf216a_get_lux(struct ltrf216a_data *data)
> +{
> +	int greendata, cleardata, lux;
> +
> +	greendata = ltrf216a_read_data(data, LTRF216A_ALS_DATA_0);
> +	cleardata = ltrf216a_read_data(data, LTRF216A_CLEAR_DATA_0);
> +
> +	if (greendata < 0 || cleardata < 0)
> +		lux = 0;
> +	else
> +		lux = greendata * 8 * WIN_FAC / data->als_gain_fac / data->int_time_fac / 10;

This could be rewritten to avoid most of the divisions.

But it also doesn't fit the calculation shown in page 20 on the
datasheet.

I suspect that 8 was calculated from a specific Window Factor (~1.77),
which is specific to one device, but I'm not sure.  The datasheet
formula is:

lux = (ALS_DATA_X * 0.45 * window_factor) / (gain * int_time)

Shouldn't WIN_FAC be a configurable parameter, instead of constant?

-- 
Gabriel Krisman Bertazi