Re: [PATCH 2/2 v2] iio: magnetometer: Add driver for Yamaha YAS5xx

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 28 Nov 2020 01:40:38 +0100
Linus Walleij <linus.walleij@linaro.org> wrote:

> This adds an IIO magnetometer driver for the Yamaha
> YAS53x magnetometer/compass chips YAS530 and YAS532.
> A quick survey of the source code released by different
> vendors reveal that we have these variants in the family
> with some deployments listed:
> 
>  * YAS529 MS-3C (2005 Samsung Aries)
>  * YAS530 MS-3E (2011 Samsung Galaxy S Advance)
>  * YAS532 MS-3R (2011 Samsung Galaxy S4)
>  * YAS533 MS-3F (Vivo 1633, 1707, V3, Y21L)
>  * (YAS534 is a magnetic switch)
>  * YAS535 MS-6C
>  * YAS536 MS-3W
>  * YAS537 MS-3T (2015 Samsung Galaxy S6, Note 5)
>  * YAS539 MS-3S (2018 Samsung Galaxy A7 SM-A750FN)
> 
> The YAS529 is so significantly different from the
> YAS53x variants that it will require its own driver.
> The YAS537 and YAS539 have slightly different register
> sets but have strong similarities so a common driver
> will probably be reasonable.
> 
> The source code for Samsung Galaxy A7's YAS539 is not
> that significantly different from the YAS530 in the
> Galaxy S Advance, so I believe we will only need this
> one driver with quirks to handle all of them.
> 
> The YAS539 is actively announced on Yamaha's devices
> site:
> https://device.yamaha.com/en/lsi/products/e_compass/
> 
> This is a driver written from scratch using buffered
> IIO and runtime PM handling regulators and reset.
> 
> Cc: phone-devel@vger.kernel.org
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Hi Linus,

Various comments inline.
The 'interesting' nature of the packing in those calibration registers
is unfortunate.  I'm not really sure how we make that code more readable
but using overlapping unaligned big endian reads definitely doesn't make
it easier for me to follow!

Jonathan

> ---
> ChangeLog v1->v3:
> - This is posted along with the DT bindings which are
>   in v3 so just number everything as v3.
> ---
>  drivers/iio/magnetometer/Kconfig         |   16 +
>  drivers/iio/magnetometer/Makefile        |    2 +
>  drivers/iio/magnetometer/yamaha-yas53x.c | 1062 ++++++++++++++++++++++
>  3 files changed, 1080 insertions(+)
>  create mode 100644 drivers/iio/magnetometer/yamaha-yas53x.c
> 
> diff --git a/drivers/iio/magnetometer/Kconfig b/drivers/iio/magnetometer/Kconfig
> index 1697a8c03506..4e32f3c8cc93 100644
> --- a/drivers/iio/magnetometer/Kconfig
> +++ b/drivers/iio/magnetometer/Kconfig
> @@ -205,4 +205,20 @@ config SENSORS_RM3100_SPI
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called rm3100-spi.
>  
> +config YAMAHA_YAS53X
> +	tristate "Yamaha YAS53x 3-Axis Magnetometers (I2C)"
> +	depends on I2C
> +	select REGMAP_I2C
> +	select IIO_BUFFER
> +	select IIO_TRIGGERED_BUFFER
> +	help
> +	  Say Y here to add support for the Yamaha YAS53x series of
> +	  3-Axis Magnetometers. Right now YAS530, YAS532 and YAS533 are
> +	  fully supported.
> +
> +	  This driver can also be compiled as a module.
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called yamaha-yas.
> +
One line only
> +
>  endmenu
> diff --git a/drivers/iio/magnetometer/Makefile b/drivers/iio/magnetometer/Makefile
> index ba1bc34b82fa..fa2656336319 100644
> --- a/drivers/iio/magnetometer/Makefile
> +++ b/drivers/iio/magnetometer/Makefile
> @@ -28,3 +28,5 @@ obj-$(CONFIG_SENSORS_HMC5843_SPI)	+= hmc5843_spi.o
>  obj-$(CONFIG_SENSORS_RM3100)		+= rm3100-core.o
>  obj-$(CONFIG_SENSORS_RM3100_I2C)	+= rm3100-i2c.o
>  obj-$(CONFIG_SENSORS_RM3100_SPI)	+= rm3100-spi.o
> +
> +obj-$(CONFIG_YAMAHA_YAS53X)		+= yamaha-yas53x.o
> diff --git a/drivers/iio/magnetometer/yamaha-yas53x.c b/drivers/iio/magnetometer/yamaha-yas53x.c
> new file mode 100644
> index 000000000000..fa718d990636
> --- /dev/null
> +++ b/drivers/iio/magnetometer/yamaha-yas53x.c
> @@ -0,0 +1,1062 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Driver for the Yamaha YAS magnetic sensors, often used in Samsung
> + * mobile phones. While all are not yet handled because of lacking
> + * hardware, expand this driver to handle the different variants:
> + *
> + * YAS529 MS-3C (2005 Samsung Aries)

You state in the intro there is little chance of sharing a driver with that one.

> + * YAS530 MS-3E (2011 Samsung Galaxy S Advance)
> + * YAS532 MS-3R (2011 Samsung Galaxy S4)
> + * YAS533 MS-3F (Vivo 1633, 1707, V3, Y21L)
> + * (YAS534 is a magnetic switch, not handled)

And there is your reason not to use wild cards in the dt file name etc!

> + * YAS535 MS-6C
> + * YAS536 MS-3W
> + * YAS537 MS-3T (2015 Samsung Galaxy S6, Note 5, Xiaomi)
> + * YAS539 MS-3S (2018 Samsung Galaxy A7 SM-A750FN)
> + *
> + * Code functions found in the MPU3050 YAS530 and YAS532 drivers
> + * named "inv_compass" in the Tegra Android kernel tree.
> + * Copyright (C) 2012 InvenSense Corporation
> + *
> + * Author: Linus Walleij <linus.walleij@linaro.org>
> + */
> +#include <linux/module.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/i2c.h>
> +#include <linux/err.h>
> +#include <linux/mutex.h>
> +#include <linux/delay.h>
> +#include <linux/bitops.h>
> +#include <linux/random.h>
> +#include <linux/regmap.h>
> +#include <linux/unaligned/be_byteshift.h>
> +#include <linux/unaligned/le_byteshift.h>
?

> +#include <linux/regulator/consumer.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/pm_runtime.h>
> +
> +#include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.h>

Don't think you need anything from that file as not doing any custom
attributes (one day I'll finally get rid of that file entirely!)

> +#include <linux/iio/buffer.h>
> +#include <linux/iio/trigger.h>

Don't think you should need that one yet as no trigger being provided by
this driver.

> +#include <linux/iio/trigger_consumer.h>
> +#include <linux/iio/triggered_buffer.h>
> +
> +/* This register map covers YAS530 and YAS532 but differs in YAS 537 and YAS539 */
> +#define YAS5XX_DEVICE_ID		0x80
> +#define YAS5XX_ACTUATE_INIT_COIL	0x81
> +#define YAS5XX_MEASURE			0x82
> +#define YAS5XX_CONFIG			0x83
> +#define YAS5XX_MEASURE_INTERVAL		0x84
> +#define YAS5XX_OFFSET_X			0x85 /* +/-31 */
> +#define YAS5XX_OFFSET_Y1		0x86 /* +/-31 */
> +#define YAS5XX_OFFSET_Y2		0x87 /* +/-31 */
> +#define YAS5XX_TEST1			0x88
> +#define YAS5XX_TEST2			0x89
> +#define YAS5XX_CAL			0x90
> +#define YAS5XX_MEASURE_DATA		0xB0
> +
> +/* Bits in the YAS5xx config register */
> +#define YAS5XX_CONFIG_INTON		BIT(0) /* Interrupt on? */
> +#define YAS5XX_CONFIG_INTHACT		BIT(1) /* Interrupt active high? */
> +#define YAS5XX_CONFIG_CCK_MASK		GENMASK(4, 2)
> +#define YAS5XX_CONFIG_CCK_SHIFT		2
> +
> +/* Bits in the measure command register */
> +#define YAS5XX_MEASURE_START		BIT(0)
> +#define YAS5XX_MEASURE_LDTC		BIT(1)
> +#define YAS5XX_MEASURE_FORS		BIT(2)
> +#define YAS5XX_MEASURE_DLYMES		BIT(4)
> +
> +/* Bits in the measure data register */
> +#define YAS5XX_MEASURE_DATA_BUSY	BIT(7)
> +
> +#define YAS530_DEVICE_ID		0x01 /* YAS530 (MS-3E) */
> +#define YAS530_VERSION_A		0 /* YAS530 (MS-3E A) */
> +#define YAS530_VERSION_B		1 /* YAS530B (MS-3E B) */
> +#define YAS530_VERSION_A_COEF		380
> +#define YAS530_VERSION_B_COEF		550
> +#define YAS530_DATA_CENTER		2048
> +#define YAS530_DATA_OVERFLOW		4095
> +
> +#define YAS532_DEVICE_ID		0x02 /* YAS532/YAS533 (MS-3R/F) */
> +#define YAS532_VERSION_AB		0 /* YAS532/533 AB (MS-3R/F AB) */
> +#define YAS532_VERSION_AC		1 /* YAS532/533 AC (MS-3R/F AC) */
> +#define YAS532_VERSION_AB_COEF		1800
> +#define YAS532_VERSION_AC_COEF_X	850
> +#define YAS532_VERSION_AC_COEF_Y1	750
> +#define YAS532_VERSION_AC_COEF_Y2	750
> +#define YAS532_DATA_CENTER		4096
> +#define YAS532_DATA_OVERFLOW		8191
> +#define YAS532_20DEGREES		390 /* Looks like Kelvin */
> +
> +/* These variant IDs are known from code dumps */
> +#define YAS537_DEVICE_ID		0x07 /* YAS537 (MS-3T) */
> +#define YAS539_DEVICE_ID		0x08 /* YAS539 (MS-3S) */
> +
> +/* Turn off device regulators etc after 5 seconds of inactivity */
> +#define YAS5XX_AUTOSUSPEND_DELAY	5000
> +
> +struct yas5xx_calibration {
> +	/* Linearization calibration x, y1, y2 */
> +	s32 r[3];
> +	u32 f[3];
> +	/* Temperature compensation calibration */
> +	s32 Cx, Cy1, Cy2;
> +	/* Misc calibration coefficients */
> +	s32 a2, a3, a4, a5, a6, a7, a8, a9, k;
> +};
> +
> +
> +/**
> + * struct yas5xx - state container for the YAS5xx driver
> + * @i2c: parent I2C client
> + * @dev: parent device pointer
> + * @devid: device ID number
> + * @version: device version
> + * @name: device name
> + * @calibration: calibration settings from the OTP storage
> + * @dck: divider clock, read from calibration
> + * @hard_offsets: offsets for each axis measured with initcoil actuated
> + * @orientation: mounting matrix, flipped axis etc
> + * @map: regmap to access the YAX5xx registers over I2C
> + * @regs: the vdd and vddio power regulators

reset missing

Make sure you run kernel-doc over this and fix anything we've missed.


> + * @lock: locks the magnetometer for exclusive use during a measurement
> + * so that measurements get serialized in a first-come-first serve manner
> + * @scan: naturally aligned measurements
> + */
> +struct yas5xx {
> +	struct i2c_client *i2c;
> +	struct device *dev;
> +	unsigned int devid;
> +	unsigned int version;
> +	char name[16];
> +	struct yas5xx_calibration calibration;
> +	u8 dck;
> +	u8 hard_offsets[3];
> +	struct iio_mount_matrix orientation;
> +	struct regmap *map;
> +	struct regulator_bulk_data regs[2];
> +	struct gpio_desc *reset;
> +	struct mutex lock;
> +	/*
> +	 * The scanout is 4 x 32 bits in CPU endianness.
> +	 * Ensure timestamp is naturally aligned
> +	 */
> +	struct {
> +		s32 channels[4];
> +		s64 ts __aligned(8);
> +	} scan;
> +};
> +
> +/* On YAS530 the x, y1 and y2 values are 12 bits */
> +static u16 yas530_extract_axis(u8 *data)
> +{
> +	u16 val;
> +
> +	/*
> +	 * These are the bits used in a 16bit word:
> +	 * 15 14 13 12 11 10 9  8  7  6  5  4  3  2  1  0
> +	 *    x  x  x  x  x  x  x  x  x  x  x  x
> +	 */
> +	val = get_unaligned_be16(&data[0]);
> +	val >>= 3;
> +	val &= GENMASK(11, 0);
> +	return val;
> +}
> +
> +/* On YAS532 the x, y1 and y2 values are 13 bits */
> +static u16 yas532_extract_axis(u8 *data)
> +{
> +	u16 val;
> +
> +	/*
> +	 * These are the bits used in a 16bit word:
> +	 * 15 14 13 12 11 10 9  8  7  6  5  4  3  2  1  0
> +	 *    x  x  x  x  x  x  x  x  x  x  x  x  x
> +	 */
> +	val = get_unaligned_be16(&data[0]);
> +	val >>= 2;
> +	val &= GENMASK(12, 0);
> +	return val;
> +}
> +
> +static int yas5xx_busy_wait(struct yas5xx *yas5xx)
> +{
> +	int maxloops = 1000;
> +	unsigned int val;
> +	int ret;
> +
> +	while (maxloops) {
> +		ret = regmap_read(yas5xx->map, YAS5XX_MEASURE_DATA, &val);
> +		if (ret)
> +			return ret;
> +
> +		if (!(val & BIT(7)))

Use a define for that magic bit.

> +			return 0;
> +
> +		maxloops--;
> +	}
> +
> +	return -ETIMEDOUT;
> +}
> +
> +/**
> + * yas5xx_measure() - Make a measure from the hardware*
stray *?
> + * @yas5xx: The device state
> + * @t: the raw temperature measurement
> + * @x: the raw x axis measurement
> + * @y1: the y1 axis measurement
> + * @y2: the y2 axis measurement
> + */
> +static int yas5xx_measure(struct yas5xx *yas5xx, u16 *t, u16 *x, u16 *y1, u16 *y2)
> +{
> +	u8 data[8];
> +	int ret;
> +	u16 val;
> +
> +	mutex_lock(&yas5xx->lock);
> +	ret = regmap_write(yas5xx->map, YAS5XX_MEASURE,
> +			   YAS5XX_MEASURE_START);
> +	if (ret < 0)
> +		goto out_unlock;
> +
> +	/* Typical time to measure 1500 us, max 2000 us */
> +	ret = yas5xx_busy_wait(yas5xx);
> +	if (ret) {
> +		dev_err(yas5xx->dev, "timeout waiting for measurement\n");
> +		goto out_unlock;
> +	}
> +
> +	ret = regmap_bulk_read(yas5xx->map, YAS5XX_MEASURE_DATA,
> +			       data, sizeof(data));
> +	if (ret)
> +		goto out_unlock;
> +
> +	mutex_unlock(&yas5xx->lock);
> +
> +	switch (yas5xx->devid) {
> +	case YAS530_DEVICE_ID:
> +		/*
> +		 * The t value is 9 bits in big endian format
> +		 * These are the bits used in a 16bit word:
> +		 * 15 14 13 12 11 10 9  8  7  6  5  4  3  2  1  0
> +		 *    x  x  x  x  x  x  x  x  x
> +		 */
> +		val = get_unaligned_be16(&data[0]);
> +		val >>= 6;
> +		val &= GENMASK(8, 0);
> +		*t = val;
> +		*x = yas530_extract_axis(&data[2]);
> +		*y1 = yas530_extract_axis(&data[4]);
> +		*y2 = yas530_extract_axis(&data[6]);
> +		break;
> +	case YAS532_DEVICE_ID:
> +		/*
> +		 * The t value is 10 bits in big endian format
> +		 * These are the bits used in a 16bit word:
> +		 * 15 14 13 12 11 10 9  8  7  6  5  4  3  2  1  0
> +		 *    x  x  x  x  x  x  x  x  x  x
> +		 */
> +		val = get_unaligned_be16(&data[0]);
> +		val >>= 5;
> +		val &= GENMASK(9, 0);
> +		*t = val;
> +		*x = yas532_extract_axis(&data[2]);
> +		*y1 = yas532_extract_axis(&data[4]);
> +		*y2 = yas532_extract_axis(&data[6]);
> +		break;
> +	default:

unlock?

> +		dev_err(yas5xx->dev, "unknown data format\n");
> +		return -EINVAL;
> +	}
> +
> +	ret = 0;

I'm fairly sure it already is.

> +
> +out_unlock:
> +	mutex_unlock(&yas5xx->lock);
> +	return ret;
> +}
> +
> +static s32 yas5xx_linearize(struct yas5xx *yas5xx, u16 val, int axis)
> +{
> +	struct yas5xx_calibration *c = &yas5xx->calibration;
> +	static const s32 yas532ac_coef[] = {
> +		YAS532_VERSION_AC_COEF_X,
> +		YAS532_VERSION_AC_COEF_Y1,
> +		YAS532_VERSION_AC_COEF_Y2,
> +	};
> +	s32 coef;
> +
> +	/* Select coefficients */
> +	switch (yas5xx->devid) {
> +	case YAS530_DEVICE_ID:
> +		if (yas5xx->version == YAS530_VERSION_A)
> +			coef = YAS530_VERSION_A_COEF;
> +		else
> +			coef = YAS530_VERSION_B_COEF;
> +		break;
> +	case YAS532_DEVICE_ID:
> +		if (yas5xx->version == YAS532_VERSION_AB)
> +			coef = YAS532_VERSION_AB_COEF;
> +		else
> +			/* Elaborate coefficients */
> +			coef = yas532ac_coef[axis];
> +		break;
> +	default:
> +		dev_err(yas5xx->dev, "unknown device type\n");
> +		break;
> +	}
> +	/*
> +	 * Linearization formula:
> +	 *
> +	 * x' = x - (3721 + 50 * f) + (xoffset - r) * c
> +	 *
> +	 * Where f and r are calibration values, c is a per-device
> +	 * and sometimes per-axis coefficient.
> +	 */
> +	return val - (3721 + 50 * c->f[axis]) +
> +		(yas5xx->hard_offsets[axis] - c->r[axis]) * coef;
> +}
> +
> +/**
/*
> + * yas5xx_get_measure() - Measure a sample of all axis and process
> + *
> + * Returned valued are in nanotesla according to some code.
> + */
> +static int yas5xx_get_measure(struct yas5xx *yas5xx, s32 *to, s32 *xo, s32 *yo, s32 *zo)
> +{
> +	struct yas5xx_calibration *c = &yas5xx->calibration;
> +	u16 t, x, y1, y2;
> +	/* These are "signed x, signed y1 etc */
> +	s32 sx, sy1, sy2, sy, sz;
> +	int ret;
> +
> +	/* We first get raw data that needs to be translated to [x,y,z] */
> +	ret = yas5xx_measure(yas5xx, &t, &x, &y1, &y2);
> +	if (ret)
> +		return ret;
> +
> +	/* Do some linearization if available */
> +	sx = yas5xx_linearize(yas5xx, x, 0);
> +	sy1 = yas5xx_linearize(yas5xx, y1, 1);
> +	sy2 = yas5xx_linearize(yas5xx, y2, 2);
> +
> +	/*
> +	 * Temperature compensation for x, y1, y2 respectively:
> +	 *
> +	 *          Cx * t
> +	 * x' = x - ------
> +	 *           100
> +	 */
> +	sx = sx - (c->Cx * t) / 100;
> +	sy1 = sy1 - (c->Cy1 * t) / 100;
> +	sy2 = sy2 - (c->Cy2 * t) / 100;
> +
> +	/*
> +	 * Break y1 and y2 into y and z, y1 and y2 are apparently encoding
> +	 * y and z.
> +	 */
> +	sy = sy1 - sy2;
> +	sz = -sy1 - sy2;
> +
> +	/*
> +	 * FIXME: convert to Celsius? Just guessing this is given
> +	 * as 1/10:s of degrees so multiply by 100 to get millicentigrades.
> +	 */
> +	*to = t * 100;
> +	/*
> +	 * Calibrate [x,y,z] with some formulas like this:
> +	 *
> +	 *            100 * x + a_2 * y + a_3 * z
> +	 *  x' = k *  ---------------------------
> +	 *                        10
> +	 *
> +	 *           a_4 * x + a_5 * y + a_6 * z
> +	 *  y' = k * ---------------------------
> +	 *                        10
> +	 *
> +	 *           a_7 * x + a_8 * y + a_9 * z
> +	 *  z' = k * ---------------------------
> +	 *                        10
> +	 */
> +	*xo = c->k * ((100 * sx + c->a2 * sy + c->a3 * sz) / 10);
> +	*yo = c->k * ((c->a4 * sx + c->a5 * sy + c->a6 * sz) / 10);
> +	*zo = c->k * ((c->a7 * sx + c->a8 * sy + c->a9 * sz) / 10);
> +
> +	return 0;
> +}
> +
> +static int yas5xx_read_raw(struct iio_dev *indio_dev,
> +			   struct iio_chan_spec const *chan,
> +			   int *val, int *val2,
> +			   long mask)
> +{
> +	struct yas5xx *yas5xx = iio_priv(indio_dev);
> +	s32 t, x, y, z;
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		pm_runtime_get_sync(yas5xx->dev);
> +		ret = yas5xx_get_measure(yas5xx, &t, &x, &y, &z);
> +		pm_runtime_mark_last_busy(yas5xx->dev);
> +		pm_runtime_put_autosuspend(yas5xx->dev);
> +		if (ret)
> +			return ret;
> +		switch (chan->address) {
> +		case 0:
> +			*val = t;
> +			break;
> +		case 1:
> +			*val = x;
> +			break;
> +		case 2:
> +			*val = y;
> +			break;
> +		case 3:
> +			*val = z;
> +			break;
> +		default:
> +			dev_err(yas5xx->dev, "unknown channel\n");
> +			return -EINVAL;
> +		}
> +		return IIO_VAL_INT;
> +	case IIO_CHAN_INFO_SCALE:
> +		if (chan->address == 0) {
> +			/* Temperature is unscaled */
> +			*val = 1;
> +			return IIO_VAL_INT;
> +		}
> +		/*
> +		 * The axis values are in nanotesla according to the vendor
> +		 * drivers, but is clearly in microtesla according to
> +		 * experiments. Since 1 uT = 0.01 Gauss, we need to divide
> +		 * by 100000000 (10^8) to get to Gauss from the raw value.
> +		 */
> +		*val = 1;
> +		*val2 = 100000000;
> +		return IIO_VAL_FRACTIONAL;
> +	default:
> +		/* Unknown request */
> +		break;
return -EINVAL would be shorter and just as clear

> +	}
> +
> +	return -EINVAL;
> +}
> +
> +static void yas5xx_fill_buffer(struct iio_dev *indio_dev)
> +{
> +	struct yas5xx *yas5xx = iio_priv(indio_dev);
> +	s32 t, x, y, z;
> +	int ret;
> +
> +	pm_runtime_get_sync(yas5xx->dev);
> +	ret = yas5xx_get_measure(yas5xx, &t, &x, &y, &z);
> +	pm_runtime_mark_last_busy(yas5xx->dev);
> +	pm_runtime_put_autosuspend(yas5xx->dev);
> +	if (ret) {
> +		dev_err(yas5xx->dev, "error refilling buffer\n");
> +		return;
> +	}
> +	yas5xx->scan.channels[0] = t;
> +	yas5xx->scan.channels[1] = x;
> +	yas5xx->scan.channels[2] = y;
> +	yas5xx->scan.channels[3] = z;
> +	iio_push_to_buffers_with_timestamp(indio_dev, &yas5xx->scan,
> +					   iio_get_time_ns(indio_dev));
> +}
> +
> +static irqreturn_t yas5xx_handle_trigger(int irq, void *p)
> +{
> +	const struct iio_poll_func *pf = p;
> +	struct iio_dev *indio_dev = pf->indio_dev;
> +
> +	yas5xx_fill_buffer(indio_dev);
> +	iio_trigger_notify_done(indio_dev->trig);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +
> +static const struct iio_mount_matrix *
> +yas5xx_get_mount_matrix(const struct iio_dev *indio_dev,
> +			const struct iio_chan_spec *chan)
> +{
> +	struct yas5xx *yas5xx = iio_priv(indio_dev);
> +
> +	return &yas5xx->orientation;
> +}
> +
> +static const struct iio_chan_spec_ext_info yas5xx_ext_info[] = {
> +	IIO_MOUNT_MATRIX(IIO_SHARED_BY_DIR, yas5xx_get_mount_matrix),
> +	{ },
> +};
> +
> +#define YAS5XX_AXIS_CHANNEL(axis, index)				\
> +	{								\
> +		.type = IIO_MAGN,					\
> +		.modified = 1,						\
> +		.channel2 = IIO_MOD_##axis,				\
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |		\
> +			BIT(IIO_CHAN_INFO_SCALE),			\
> +		.ext_info = yas5xx_ext_info,				\
> +		.address = index,					\
> +		.scan_index = index,					\
> +		.scan_type = {						\
> +			.sign = 's',					\
> +			.realbits = 32,					\
> +			.storagebits = 32,				\
> +			.endianness = IIO_CPU				\
> +		},							\
> +	}
> +
> +static const struct iio_chan_spec yas5xx_channels[] = {
> +	{
> +		.type = IIO_TEMP,
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
> +		.address = 0,
> +		.scan_index = 0,
> +		.scan_type = {
> +			.sign = 'u',
> +			.realbits = 32,
> +			.storagebits = 32,
> +			.endianness = IIO_CPU
> +		},
> +	},
> +	YAS5XX_AXIS_CHANNEL(X, 1),
> +	YAS5XX_AXIS_CHANNEL(Y, 2),
> +	YAS5XX_AXIS_CHANNEL(Z, 3),
> +	IIO_CHAN_SOFT_TIMESTAMP(4),
> +};
> +
> +static const unsigned long yas5xx_scan_masks[] = { 0xf, 0 };
> +
> +static const struct iio_info yas5xx_info = {
> +	.read_raw = &yas5xx_read_raw,
> +};
> +
> +static bool yas5xx_volatile_reg(struct device *dev, unsigned int reg)
> +{
> +	return reg == YAS5XX_ACTUATE_INIT_COIL ||
> +		reg == YAS5XX_MEASURE ||
> +		(reg >= YAS5XX_MEASURE_DATA &&
> +		 reg <= YAS5XX_MEASURE_DATA + 8);
> +}
> +
> +/* FIXME: enable regmap cache, using mark dirty and sync at runtime resume */
> +static const struct regmap_config yas5xx_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +	.max_register = 0xff,
> +	.volatile_reg = yas5xx_volatile_reg,
> +};
> +
> +/**
> + * yas5xx_extract_bits() - Extracts an u8 from an u16 pointer

__be16 pointer

> + *
> + * @data: pointer to two consecutive BE u8 forming an u16
> + * @start: first bit to extract
> + * @end: last bit to extract
> + *
> + * For example extract bits 6 to 9:
> + * 15 14 13 12 11 10 9  8  7  6  5  4  3  2  1  0
> + *                   x  x  x  x
> + * u8 e = yas5xx_extract_bits(data, 6, 9);
> + */
> +static u8 yas5xx_extract_bits(u8 *data, int start, int end)
> +{
> +	u16 val;
> +
> +	val = get_unaligned_be16(data);
> +	val &= GENMASK(end, start);
> +	val >>= start;
> +	return (u8)val;
> +}
> +
> +/**
> + * yas53x_extract_calibration() - extracts the a2-a9 and k calibration
> + * @data: the bitfield to use
> + * @c: the calibration to populate
> + */
> +static void yas53x_extract_calibration(u8 *data, struct yas5xx_calibration *c)
> +{

As below.  I'm not sure how you make this clearer, but right now it's
really hard to follow.  Perhaps detailed comment on what the data packing
in here is?

> +	c->a2 = yas5xx_extract_bits(&data[3], 10, 15) - 32;
> +	c->a3 = yas5xx_extract_bits(&data[3], 6, 9) - 8;
> +	c->a4 = yas5xx_extract_bits(&data[4], 8, 13) - 32;
> +	c->a5 = yas5xx_extract_bits(&data[5], 10, 15) + 38;
> +	c->a6 = yas5xx_extract_bits(&data[5], 4, 9) - 32;
> +	c->a7 = yas5xx_extract_bits(&data[6], 5, 11) - 64;
> +	c->a8 = yas5xx_extract_bits(&data[7], 7, 12) - 32;
> +	c->a9 = yas5xx_extract_bits(&data[8], 7, 14);
> +	c->k = yas5xx_extract_bits(&data[9], 10, 14) + 10;
> +}
> +
> +static int yas530_get_calibration_data(struct yas5xx *yas5xx)
> +{
> +	struct yas5xx_calibration *c = &yas5xx->calibration;
> +	u8 data[16];
> +	int ret;
> +
> +	/* Dummy read, first read is ALWAYS wrong */
> +	ret = regmap_bulk_read(yas5xx->map, YAS5XX_CAL,
> +			       data, sizeof(data));
> +	if (ret)
> +		return ret;
> +	/* Actual calibration readout */
> +	ret = regmap_bulk_read(yas5xx->map, YAS5XX_CAL,
> +			       data, sizeof(data));
> +	if (ret)
> +		return ret;
> +	dev_dbg(yas5xx->dev, "calibration data: %*ph\n", 14, data);
> +
> +	add_device_randomness(data, sizeof(data));
> +	yas5xx->version = data[15] & 0x03;
> +	yas5xx->dck = yas5xx_extract_bits(&data[9], 7, 9);
> +
> +	/* Extract the calibration from the bitfield */
> +	c->Cx = data[0] * 6 - 768;
> +	c->Cy1 = data[1] * 6 - 768;
> +	c->Cy2 = data[2] * 6 - 768;
> +	yas53x_extract_calibration(data, c);
> +	/* Extract linearization */
> +	c->f[0] = yas5xx_extract_bits(&data[11], 13, 14);
> +	/* 6 bit value where bit 5 is the sign */

As below, I wonder if you'd be better just constructing these directly from
the 8 bit register pairs. The overlapping unaligned 16 bit reads are
rather confusing.

> +	c->r[0] = sign_extend32(yas5xx_extract_bits(&data[11], 7, 12), 5);
> +	c->f[1] = yas5xx_extract_bits(&data[12], 13, 14);
> +	c->r[1] = sign_extend32(yas5xx_extract_bits(&data[12], 7, 12), 5);
> +	c->f[2] = yas5xx_extract_bits(&data[13], 13, 14);
> +	c->r[2] = sign_extend32(yas5xx_extract_bits(&data[13], 7, 12), 5);
> +
> +	return 0;
> +}
> +
> +static int yas532_get_calibration_data(struct yas5xx *yas5xx)
> +{
> +	struct yas5xx_calibration *c = &yas5xx->calibration;
> +	u8 data[14];
> +	int ret;
> +	int i;
> +
> +	/* Dummy read, first read is ALWAYS wrong */
> +	ret = regmap_bulk_read(yas5xx->map, YAS5XX_CAL,
> +			       data, sizeof(data));

My quick check suggests that is under 80 chars when on one line which
would definitely be nicer.

> +	if (ret)
> +		return ret;

blank line here

> +	/* Actual calibration readout */
> +	ret = regmap_bulk_read(yas5xx->map, YAS5XX_CAL,
> +			       data, sizeof(data));
> +	if (ret)
> +		return ret;
> +	dev_dbg(yas5xx->dev, "calibration data: %*ph\n", 14, data);
> +
> +	/* Sanity check */
> +	for (i = 0; i < 13; i++) {
> +		if (data[i] != 0)
> +			break;
> +	}
> +	if (i == 13 && !(data[13] & BIT(7)))
> +		dev_err(yas5xx->dev, "calibration is blank!\n");
> +
> +	add_device_randomness(data, sizeof(data));
> +	/* Only versions 0 and 1 */

Comment needs a bit more... Do other versions exist?

> +	yas5xx->version = data[13] & 0x01;
> +	yas5xx->dck = yas5xx_extract_bits(&data[9], 7, 9);
> +
> +	/* Extract calibration from the bitfield */
> +	c->Cx = data[0] * 10 - 1280;
> +	c->Cy1 = data[1] * 10 - 1280;
> +	c->Cy2 = data[2] * 10 - 1280;
> +	yas53x_extract_calibration(data, c);
> +	/* Extract linearization */

Could you add a comment on the data layout here. It seems rather
non obvious given the overlapping 16 bit reads you are doing.
Whilst the maths might correspond to extracting bits from be16 registers
that looks more like coincidence than design and only makes any
useful difference to the bit 7,8 pair.  The bit 9-14 could just have
been gotten from the next 8 bit register directly.


> +	c->f[0] = yas5xx_extract_bits(&data[10], 7, 8);
> +	/* 6 bit value where bit 5 is the sign */
> +	c->r[0] = (s8) sign_extend32(yas5xx_extract_bits(&data[10], 9, 14), 5);

> +	c->f[1] = yas5xx_extract_bits(&data[11], 7, 8);
> +	c->r[1] = (s8) sign_extend32(yas5xx_extract_bits(&data[11], 9, 14), 5);
> +	c->f[2] = yas5xx_extract_bits(&data[12], 7, 8);
> +	c->r[2] = (s8) sign_extend32(yas5xx_extract_bits(&data[12], 9, 14), 5);
> +
> +	return 0;
> +}
> +
> +void yas5xx_dump_calibration(struct yas5xx *yas5xx)
> +{
> +	struct yas5xx_calibration *c = &yas5xx->calibration;
> +
> +	dev_dbg(yas5xx->dev, "f[] = [%d, %d, %d]\n",
> +		c->f[0], c->f[1], c->f[2]);
> +	dev_dbg(yas5xx->dev, "r[] = [%d, %d, %d]\n",
> +		c->r[0], c->r[1], c->r[2]);
> +	dev_dbg(yas5xx->dev, "Cx = %d\n", c->Cx);
> +	dev_dbg(yas5xx->dev, "Cy1 = %d\n", c->Cy1);
> +	dev_dbg(yas5xx->dev, "Cy2 = %d\n", c->Cy2);
> +	dev_dbg(yas5xx->dev, "a2 = %d\n", c->a2);
> +	dev_dbg(yas5xx->dev, "a3 = %d\n", c->a3);
> +	dev_dbg(yas5xx->dev, "a4 = %d\n", c->a4);
> +	dev_dbg(yas5xx->dev, "a5 = %d\n", c->a5);
> +	dev_dbg(yas5xx->dev, "a6 = %d\n", c->a6);
> +	dev_dbg(yas5xx->dev, "a7 = %d\n", c->a7);
> +	dev_dbg(yas5xx->dev, "a8 = %d\n", c->a8);
> +	dev_dbg(yas5xx->dev, "a9 = %d\n", c->a9);
> +	dev_dbg(yas5xx->dev, "k = %d\n", c->k);
> +}
> +
> +static int yas5xx_set_offsets(struct yas5xx *yas5xx, s8 ox, s8 oy1, s8 oy2)
> +{
> +	int ret;
> +
> +	ret = regmap_write(yas5xx->map, YAS5XX_OFFSET_X, ox);
> +	if (ret)
> +		return ret;
> +	ret = regmap_write(yas5xx->map, YAS5XX_OFFSET_Y1, oy1);
> +	if (ret)
> +		return ret;
> +	ret = regmap_write(yas5xx->map, YAS5XX_OFFSET_Y2, oy2);
> +	if (ret)
> +		return ret;

return regmap_write() for last one.

> +
> +	return 0;
> +}
> +
> +static s8 yas5xx_adjust_offset(s8 old, int bit, u16 center, u16 measure)
> +{
> +	if (measure > center)
> +		return old + BIT(bit);
> +	if (measure < center)
> +		return old - BIT(bit);
> +	return old;
> +}
> +
> +static int yas5xx_meaure_offsets(struct yas5xx *yas5xx)
> +{
> +	int ret;
> +	u16 center;
> +	u16 t, x, y1, y2;
> +	s8 ox, oy1, oy2;
> +	int i;
> +
> +	/* Actuate the init coil and measure offsets */
> +	ret = regmap_write(yas5xx->map, YAS5XX_ACTUATE_INIT_COIL, 0);
> +	if (ret)
> +		return ret;
> +
> +	/* When the initcoil is active this should be around the center */
> +	switch (yas5xx->devid) {
> +	case YAS530_DEVICE_ID:
> +		center = YAS530_DATA_CENTER;
> +		break;
> +	case YAS532_DEVICE_ID:
> +		center = YAS532_DATA_CENTER;
> +		break;
> +	default:
> +		dev_err(yas5xx->dev, "unknown device type\n");
> +		return -EINVAL;
> +	}
> +
> +	/*
> +	 * We set offsets in the interval +-31 by iterating
> +	 * +-16, +-8, +-4, +-2, +-1 adjusting the offsets each
> +	 * time, then writing the final offsets into the
> +	 * registers.
> +	 *
> +	 * NOTE: these offsets are NOT in the same unit or magnitude
> +	 * as the values for [x, y1, y2]. The value is +/-31
> +	 * but the effect on the raw values is much larger.
> +	 * The effect of the offset is to bring the measure
> +	 * rougly to the center.
> +	 */
> +	ox = 0;
> +	oy1 = 0;
> +	oy2 = 0;
> +
> +	for (i = 4; i >= 0; i--) {
> +		ret = yas5xx_set_offsets(yas5xx, ox, oy1, oy2);
> +		if (ret)
> +			return ret;
> +
> +		ret = yas5xx_measure(yas5xx, &t, &x, &y1, &y2);
> +		if (ret)
> +			return ret;
> +		dev_dbg(yas5xx->dev, "measurement %d: x=%d, y1=%d, y2=%d\n",
> +			5-i, x, y1, y2);
> +
> +		ox = yas5xx_adjust_offset(ox, i, center, x);
> +		oy1 = yas5xx_adjust_offset(oy1, i, center, y1);
> +		oy2 = yas5xx_adjust_offset(oy2, i, center, y2);
> +	}
> +
> +	/* Needed for calibration algorithm */
> +	yas5xx->hard_offsets[0] = ox;
> +	yas5xx->hard_offsets[1] = oy1;
> +	yas5xx->hard_offsets[2] = oy2;
> +	ret = yas5xx_set_offsets(yas5xx, ox, oy1, oy2);
> +	if (ret)
> +		return ret;
> +
> +	dev_info(yas5xx->dev, "discovered hard offsets: x=%d, y1=%d, y2=%d\n",
> +		 ox, oy1, oy2);
> +	return 0;
> +}
> +
> +static int yas5xx_power_on(struct yas5xx *yas5xx)
> +{
> +	unsigned int val;
> +	int ret;
> +
> +	/* Zero the test registers */
> +	ret = regmap_write(yas5xx->map, YAS5XX_TEST1, 0);
> +	if (ret)
> +		return ret;
> +	ret = regmap_write(yas5xx->map, YAS5XX_TEST2, 0);
> +	if (ret)
> +		return ret;
> +
> +	/* Set up for no interrupts, calibrated clock divider */
> +	val = (yas5xx->dck << YAS5XX_CONFIG_CCK_SHIFT) & YAS5XX_CONFIG_CCK_MASK;

FIELD_SET would make that a tiny bit easier to read.
May not be worth bothering with the local variable either.

> +	ret = regmap_write(yas5xx->map, YAS5XX_CONFIG, val);
> +	if (ret)
> +		return ret;
> +
> +	/* Measure interval 0 (back-to-back?)  */
> +	ret = regmap_write(yas5xx->map, YAS5XX_MEASURE_INTERVAL, 0);
> +	if (ret)
> +		return ret;
return regmap_write()
for last line.
> +
> +	return 0;
> +}
> +
> +static int yas5xx_probe(struct i2c_client *i2c,
> +			const struct i2c_device_id *id)
> +{
> +	struct iio_dev *indio_dev;
> +	struct device *dev = &i2c->dev;
> +	struct yas5xx *yas5xx;
> +	int ret;
> +
> +	indio_dev = devm_iio_device_alloc(&i2c->dev, sizeof(*yas5xx));
> +	if (indio_dev == NULL)
> +		return -ENOMEM;
> +
> +	yas5xx = iio_priv(indio_dev);
> +	i2c_set_clientdata(i2c, indio_dev);
> +	yas5xx->i2c = i2c;
> +	yas5xx->dev = dev;

Perhaps a bit excessive to have pointers to dev and i2c_client given
i2c->dev is available.

> +	mutex_init(&yas5xx->lock);
> +
> +	ret = iio_read_mount_matrix(dev, "mount-matrix", &yas5xx->orientation);
> +	if (ret)
> +		return ret;
> +
> +	yas5xx->regs[0].supply = "vdd";
> +	yas5xx->regs[1].supply = "iovdd";
> +	ret = devm_regulator_bulk_get(dev,
> +				      ARRAY_SIZE(yas5xx->regs),
> +				      yas5xx->regs);

More line breaks than we need in that.

> +	if (ret)
> +		return dev_err_probe(dev, ret, "cannot get regulators\n");
> +
> +	ret = regulator_bulk_enable(ARRAY_SIZE(yas5xx->regs), yas5xx->regs);
> +	if (ret) {
> +		dev_err(dev, "cannot enable regulators\n");
> +		return ret;
> +	}
> +
> +	/* See comment in runtime resume callback */
> +	usleep_range(31000, 40000);
> +
> +	/* This will take the device out of reset if need be */
> +	yas5xx->reset = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_LOW);
> +	if (IS_ERR(yas5xx->reset)) {
> +		ret = dev_err_probe(dev, PTR_ERR(yas5xx->reset),
> +				    "failed to get reset line\n");
> +		goto reg_off;
> +	}
> +
> +	yas5xx->map = devm_regmap_init_i2c(i2c, &yas5xx_regmap_config);
> +	if (IS_ERR(yas5xx->map)) {
> +		dev_err(dev, "failed to allocate register map\n");
> +		ret = PTR_ERR(yas5xx->map);
> +		goto reg_off;
> +	}
> +
> +	ret = regmap_read(yas5xx->map, YAS5XX_DEVICE_ID, &yas5xx->devid);
> +	if (ret)
> +		goto reg_off;
> +
> +	switch (yas5xx->devid) {
> +	case YAS530_DEVICE_ID:
> +		ret = yas530_get_calibration_data(yas5xx);
> +		if (ret)
> +			goto reg_off;
> +		snprintf(yas5xx->name, sizeof(yas5xx->name),
> +			 "YAS530 MS-3E %s",

Name tends to be lowercase. Also, not sure we've had one with spaces
in it before.  I guess our userspace code is fine with it though
as presumably you've tested that.

> +			 yas5xx->version ? "B" : "A");
> +		break;
> +	case YAS532_DEVICE_ID:
> +		ret = yas532_get_calibration_data(yas5xx);
> +		if (ret)
> +			goto reg_off;
> +		snprintf(yas5xx->name, sizeof(yas5xx->name),
> +			 "YAS532/YAS533 MS-3R/F %s",
> +			 yas5xx->version ? "AC" : "AB");
> +		break;
> +	default:
> +		dev_err(dev, "unhandled device ID %02x\n", yas5xx->devid);
> +		goto reg_off;
> +	}
> +
> +	yas5xx_dump_calibration(yas5xx);
> +	ret = yas5xx_power_on(yas5xx);
> +	if (ret)
> +		goto reg_off;
> +	ret = yas5xx_meaure_offsets(yas5xx);
> +	if (ret)
> +		goto reg_off;
> +	dev_info(dev, "detected %s\n", yas5xx->name);
> +
> +	indio_dev->info = &yas5xx_info;
> +	indio_dev->available_scan_masks = yas5xx_scan_masks;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->name = yas5xx->name;
> +	indio_dev->channels = yas5xx_channels;
> +	indio_dev->num_channels = ARRAY_SIZE(yas5xx_channels);
> +
> +	ret = iio_triggered_buffer_setup(indio_dev, NULL,
> +					 yas5xx_handle_trigger,
> +					 NULL);
> +	if (ret) {
> +		dev_err(dev, "triggered buffer setup failed\n");
> +		goto reg_off;
> +	}
> +
> +	ret = iio_device_register(indio_dev);
> +	if (ret) {
> +		dev_err(dev, "device register failed\n");
> +		goto cleanup_buffer;
> +	}
> +
> +	/* Take runtime PM online */
> +	pm_runtime_get_noresume(dev);
> +	pm_runtime_set_active(dev);
> +	pm_runtime_enable(dev);
> +
> +	pm_runtime_set_autosuspend_delay(dev, YAS5XX_AUTOSUSPEND_DELAY);
> +	pm_runtime_use_autosuspend(dev);
> +	pm_runtime_put(dev);
> +
> +	return 0;
> +
> +cleanup_buffer:
> +	iio_triggered_buffer_cleanup(indio_dev);
> +reg_off:
> +	regulator_bulk_disable(ARRAY_SIZE(yas5xx->regs), yas5xx->regs);
> +
> +	return ret;
> +}
> +
> +static int yas5xx_remove(struct i2c_client *i2c)
> +{
> +	struct iio_dev *indio_dev = i2c_get_clientdata(i2c);
> +	struct yas5xx *yas5xx = iio_priv(indio_dev);
> +	struct device *dev = &i2c->dev;
> +
> +	iio_device_unregister(indio_dev);
> +	iio_triggered_buffer_cleanup(indio_dev);
> +	pm_runtime_get_sync(dev);
> +	pm_runtime_put_noidle(dev);
> +	pm_runtime_disable(dev);
> +	if (yas5xx->reset)
> +		gpiod_set_value_cansleep(yas5xx->reset, 1);
> +	regulator_bulk_disable(ARRAY_SIZE(yas5xx->regs), yas5xx->regs);
> +
> +	return 0;
> +}
> +
> +static int __maybe_unused yas5xx_runtime_suspend(struct device *dev)
> +{
> +	struct iio_dev *indio_dev = i2c_get_clientdata(to_i2c_client(dev));

There was a bit of a move to drop the circularity of what is going on here
and replace them with dev_get_devdata(dev) rather than going out to the
i2c_client devices and back to the dev again.

> +	struct yas5xx *yas5xx = iio_priv(indio_dev);
> +
> +	if (yas5xx->reset)
> +		gpiod_set_value_cansleep(yas5xx->reset, 1);
> +	regulator_bulk_disable(ARRAY_SIZE(yas5xx->regs), yas5xx->regs);
> +
> +	return 0;
> +}
> +
> +static int __maybe_unused yas5xx_runtime_resume(struct device *dev)
> +{
> +	struct iio_dev *indio_dev = i2c_get_clientdata(to_i2c_client(dev));
> +	struct yas5xx *yas5xx = iio_priv(indio_dev);
> +	int ret;
> +
> +	ret = regulator_bulk_enable(ARRAY_SIZE(yas5xx->regs), yas5xx->regs);
> +	if (ret) {
> +		dev_err(dev, "cannot enable regulators\n");
> +		return ret;
> +	}

blank line

> +	/*
> +	 * The YAS530 datasheet says TVSKW is up to 30 ms, after that 1 ms
> +	 * for all voltages to settle. The YAS532 is 10ms then 4ms for the
> +	 * I2C to come online. Let's keep it safe and put this at 31ms.
> +	 */
> +	usleep_range(31000, 40000);
> +	if (yas5xx->reset)
> +		gpiod_set_value_cansleep(yas5xx->reset, 0);
> +
> +	regmap_read(yas5xx->map, YAS5XX_DEVICE_ID, &yas5xx->devid);

Why this read?  I'm guessing it might be a required part of the power up?
If so add a comment.

> +	ret = yas5xx_power_on(yas5xx);
> +	if (ret) {
> +		dev_err(dev, "cannot power on\n");
> +		goto out_reset;
> +	}
> +
> +	return 0;
> +
> +out_reset:
> +	if (yas5xx->reset)
> +		gpiod_set_value_cansleep(yas5xx->reset, 1);
> +	regulator_bulk_disable(ARRAY_SIZE(yas5xx->regs), yas5xx->regs);
> +
> +	return ret;
> +}
> +
> +static const struct dev_pm_ops yas5xx_dev_pm_ops = {
> +	SET_SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend,
> +				pm_runtime_force_resume)
> +	SET_RUNTIME_PM_OPS(yas5xx_runtime_suspend,
> +			   yas5xx_runtime_resume, NULL)
> +};
> +
> +static const struct i2c_device_id yas5xx_id[] = {
> +	{"yas530", 0 },

No need to provide the 0s though I guess you can keep them if expectation
is you'll add other parts shortly.  However, if you are doing that introduce
an enum now.

> +	{"yas532", 0 },
> +	{"yas533", 0 },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(i2c, yas5xx_id);
> +
> +static const struct of_device_id yas5xx_of_match[] = {
> +	{ .compatible = "yamaha,yas530", },
> +	{ .compatible = "yamaha,yas532", },
> +	{ .compatible = "yamaha,yas533", },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(of, yas5xx_of_match);
> +
> +static struct i2c_driver yas5xx_driver = {
> +	.driver	 = {
> +		.name	= "yas5xx",
> +		.of_match_table = yas5xx_of_match,
> +		.pm = &yas5xx_dev_pm_ops,
> +	},
> +	.probe	  = yas5xx_probe,
> +	.remove	  = yas5xx_remove,
> +	.id_table = yas5xx_id,
> +};
> +module_i2c_driver(yas5xx_driver);
> +
> +MODULE_DESCRIPTION("Yamaha YAS53x 3-axis magnetometer driver");
> +MODULE_AUTHOR("Linus Walleij");
> +MODULE_LICENSE("GPL v2");