linux-kernel - Re: [PATCH v4 2/2] iio: magnetometer: si7210: add driver for Si7210

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Message-ID: <20250116200558.mr23jxpdpwyu62md@antoni-VivoBook-ASUSLaptop-X512FAY-K512FA>
Date: Thu, 16 Jan 2025 21:05:58 +0100
From: Antoni Pokusinski <apokusinski01@...il.com>
To: Andy Shevchenko <andy@...nel.org>, jic23@...nel.org, lars@...afoo.de,
	robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
	andrej.skvortzov@...il.com, neil.armstrong@...aro.org,
	icenowy@...c.io, megi@....cz, danila@...xyga.com,
	javier.carrasco.cruz@...il.com, linux-kernel@...r.kernel.org,
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v4 2/2] iio: magnetometer: si7210: add driver for Si7210

On Thu, Jan 16, 2025 at 10:26:55AM +0200, Andy Shevchenko wrote:
> On Wed, Jan 15, 2025 at 09:16:22PM +0100, Antoni Pokusinski wrote:
> > Silicon Labs Si7210 is an I2C Hall effect magnetic position and
> > temperature sensor. The driver supports the following functionalities:
> > * reading the temperature measurements
> > * reading the magnetic field measurements in a single-shot mode
> > * choosing the magnetic field measurement scale (20 or 200 mT)
> 
> ...
> 
> > +obj-$(CONFIG_SI7210) 			+= si7210.o
> 
> Looks like TAB/space mixture in the middle.
> 
> ...
> 
> > +#include <asm/byteorder.h>
> 
> asm/* usually goes after linux/*
> 
> > +#include <linux/array_size.h>
> > +#include <linux/bitfield.h>
> > +#include <linux/bits.h>
> > +#include <linux/cleanup.h>
> > +#include <linux/err.h>
> > +#include <linux/i2c.h>
> > +#include <linux/iio/iio.h>
> > +#include <linux/math64.h>
> > +#include <linux/mod_devicetable.h>
> > +#include <linux/mutex.h>
> > +#include <linux/regmap.h>
> > +#include <linux/regulator/consumer.h>
> > +#include <linux/types.h>
> > +#include <linux/units.h>
> 
> ...
> 
> Despite a good formatting I would still add a comment with a formula in
> math-human-readable form.
> 
> > +		temp = FIELD_GET(GENMASK(14, 3), dspsig);
> > +		temp = div_s64(-383 * temp * temp, 100) + 160940 * temp - 279800000;
> > +		temp *= (1 + (data->temp_gain / 2048));
> > +		temp += (int)(MICRO / 16) * data->temp_offset;
> 
> > +		ret = regulator_get_voltage(data->vdd);
> > +		if (ret < 0)
> > +			return ret;
> > +
> > +		temp -= 222 * div_s64(ret, MILLI);
> 
> Including this piece.
> 
> > +		*val = div_s64(temp, MILLI);
> 
> ...
> 
> > +static int si7210_set_scale(struct si7210_data *data, unsigned int scale)
> > +{
> > +	s8 *a_otp_values;
> > +	int ret;
> > +
> > +	if (scale == 20)
> > +		a_otp_values = data->scale_20_a;
> > +	else if (scale == 200)
> > +		a_otp_values = data->scale_200_a;
> > +	else
> > +		return -EINVAL;
> > +
> > +	guard(mutex)(&data->fetch_lock);
> > +
> > +	/* Write the registers 0xCA - 0xCC */
> > +	ret = regmap_bulk_write(data->regmap, SI7210_REG_A0, a_otp_values, 3);
> > +	if (ret)
> > +		return ret;
> 
> > +	/* Write the registers 0xCE - 0xD0 */
> > +	ret = regmap_bulk_write(data->regmap, SI7210_REG_A3, &a_otp_values[3], 3);
> > +	if (ret)
> > +		return ret;
> 
> Just to be sure I understand the above. There are two of 24-bit values or there are
> two sets of 3 byte arrays? How does datasheet refers to them? What does common sense
> tell us here?
> 

It's the second option: we have 2 arrays of 3 elements each (a0, a1, a2
and a3, a4, a5). In the datasheet the names of the values correspond
to the names I used in the driver, that is there are 6 values a0, ..., a5.

The point is that the their registers are separated by the 0xCD register.
Therefore I had to call `regmap_bulk_write()` twice in order to
write values a0 - a2 to the registers 0xCA - 0xCC and similarly the
values a3 - a5 to the regs 0xCE - 0xD0.

> > +	data->curr_scale = scale;
> > +
> > +	return 0;
> > +}
> 
> ...
> 
> Overall LGTM, there is no need for resend as I believe the three things above
> may be tweaked by Jonathan. The last one can go even if there are 2 24-bit
> values, but ideally in that case we should use those as a such and apply
> put_unaligned_be24/le24() whichever suits better.
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
> 
> 
Kind regards,
Antoni