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Date:   Sat, 3 Nov 2018 17:19:00 +0000
From:   Jonathan Cameron <jic23@kernel.org>
To:     Song Qiang <songqiang1304521@gmail.com>
Cc:     knaack.h@gmx.de, lars@metafoo.de, pmeerw@pmeerw.net,
        robh+dt@kernel.org, mark.rutland@arm.com, preid@electromag.com.au,
        himanshujha199640@gmail.com, linux-iio@vger.kernel.org,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org
Subject: Re: [PATCH v5 3/3] iio: magnetometer: Add driver support for PNI
 RM3100
Message-ID: <20181103171900.601537e3@archlinux>
In-Reply-To: <20181102074209.12620-4-songqiang1304521@gmail.com>
References: <20181102074209.12620-1-songqiang1304521@gmail.com>
        <20181102074209.12620-4-songqiang1304521@gmail.com>
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On Fri,  2 Nov 2018 15:42:09 +0800
Song Qiang <songqiang1304521@gmail.com> wrote:

> PNI RM3100 is a high resolution, large signal immunity magnetometer,
> composed of 3 single sensors and a processing chip with a MagI2C
> interface.
> 
> Following functions are available:
>  - Single-shot measurement from
>    /sys/bus/iio/devices/iio:deviceX/in_magn_{axis}_raw
>  - Triggerd buffer measurement.
>  - DRDY pin for data ready trigger.
>  - Both i2c and spi interface are supported.
>  - Both interrupt and polling measurement is supported, depends on if
>    the 'interrupts' in DT is declared.
> 
> Signed-off-by: Song Qiang <songqiang1304521@gmail.com>

Hi Song.

I think the optimized read of X and Z actually puts the data in the
wrong locations, should be XXXxZZZx but I think you have XXXxxxxxZZZx
I would just fix that up, but I can't test it - so back to you one more
time!

The currentmode thing looks like a core bug to me.  All devices should come
up in DIRECTMODE.  Even for devices that don't actually support direct reading
they can't come up in buffered mode because there will be configuration to do.
Right now they come up in no mode at all - hence your fix.

A default of DIRECTMODE makes sense to me - probably wants to be set in
the initial allocation code so if there is a reason to override it that can
still be done.  Fine to have it set in your driver until that fix is in
place in the core.

A few totally trivial other things I would just have fixed if we didn't have
the axis question.

Jonathan

> ---
>  MAINTAINERS                            |   7 +
>  drivers/iio/magnetometer/Kconfig       |  29 ++
>  drivers/iio/magnetometer/Makefile      |   4 +
>  drivers/iio/magnetometer/rm3100-core.c | 613 +++++++++++++++++++++++++
>  drivers/iio/magnetometer/rm3100-i2c.c  |  54 +++
>  drivers/iio/magnetometer/rm3100-spi.c  |  64 +++
>  drivers/iio/magnetometer/rm3100.h      |  17 +
>  7 files changed, 788 insertions(+)
>  create mode 100644 drivers/iio/magnetometer/rm3100-core.c
>  create mode 100644 drivers/iio/magnetometer/rm3100-i2c.c
>  create mode 100644 drivers/iio/magnetometer/rm3100-spi.c
>  create mode 100644 drivers/iio/magnetometer/rm3100.h
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 1c0f771b859e..ca7a31736256 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -11824,6 +11824,13 @@ M:	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
>  S:	Maintained
>  F:	drivers/pnp/
>  
> +PNI RM3100 IIO DRIVER
> +M:	Song Qiang <songqiang1304521@gmail.com>
> +L:	linux-iio@vger.kernel.org
> +S:	Maintained
> +F:	drivers/iio/magnetometer/rm3100*
> +F:	Documentation/devicetree/bindings/iio/magnetometer/pni,rm3100.txt
> +
>  POSIX CLOCKS and TIMERS
>  M:	Thomas Gleixner <tglx@linutronix.de>
>  L:	linux-kernel@vger.kernel.org
> diff --git a/drivers/iio/magnetometer/Kconfig b/drivers/iio/magnetometer/Kconfig
> index ed9d776d01af..8a63cbbca4b7 100644
> --- a/drivers/iio/magnetometer/Kconfig
> +++ b/drivers/iio/magnetometer/Kconfig
> @@ -175,4 +175,33 @@ config SENSORS_HMC5843_SPI
>  	  - hmc5843_core (core functions)
>  	  - hmc5843_spi (support for HMC5983)
>  
> +config SENSORS_RM3100
> +	tristate
> +	select IIO_BUFFER
> +	select IIO_TRIGGERED_BUFFER
> +
> +config SENSORS_RM3100_I2C
> +	tristate "PNI RM3100 3-Axis Magnetometer (I2C)"
> +	depends on I2C
> +	select SENSORS_RM3100
> +	select REGMAP_I2C
> +	help
> +	  Say Y here to add support for the PNI RM3100 3-Axis Magnetometer.
> +
> +	  This driver can also be compiled as a module.
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called rm3100-i2c.
> +
> +config SENSORS_RM3100_SPI
> +	tristate "PNI RM3100 3-Axis Magnetometer (SPI)"
> +	depends on SPI_MASTER
> +	select SENSORS_RM3100
> +	select REGMAP_SPI
> +	help
> +	  Say Y here to add support for the PNI RM3100 3-Axis Magnetometer.
> +
> +	  This driver can also be compiled as a module.
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called rm3100-spi.
> +
>  endmenu
> diff --git a/drivers/iio/magnetometer/Makefile b/drivers/iio/magnetometer/Makefile
> index 664b2f866472..ba1bc34b82fa 100644
> --- a/drivers/iio/magnetometer/Makefile
> +++ b/drivers/iio/magnetometer/Makefile
> @@ -24,3 +24,7 @@ obj-$(CONFIG_IIO_ST_MAGN_SPI_3AXIS) += st_magn_spi.o
>  obj-$(CONFIG_SENSORS_HMC5843)		+= hmc5843_core.o
>  obj-$(CONFIG_SENSORS_HMC5843_I2C)	+= hmc5843_i2c.o
>  obj-$(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
> diff --git a/drivers/iio/magnetometer/rm3100-core.c b/drivers/iio/magnetometer/rm3100-core.c
> new file mode 100644
> index 000000000000..8523548b7fb7
> --- /dev/null
> +++ b/drivers/iio/magnetometer/rm3100-core.c
> @@ -0,0 +1,613 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * PNI RM3100 3-axis geomagnetic sensor driver core.
> + *
> + * Copyright (C) 2018 Song Qiang <songqiang1304521@gmail.com>
> + *
> + * User Manual available at
> + * <https://www.pnicorp.com/download/rm3100-user-manual/>
> + *
> + * TODO: event generation, pm.
> + */
> +
> +#include <linux/delay.h>
> +#include <linux/interrupt.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +
> +#include <linux/iio/buffer.h>
> +#include <linux/iio/iio.h>
> +#include <linux/iio/kfifo_buf.h>
> +#include <linux/iio/sysfs.h>
> +#include <linux/iio/trigger.h>
> +#include <linux/iio/triggered_buffer.h>
> +#include <linux/iio/trigger_consumer.h>
> +
> +#include "rm3100.h"
> +
> +/* Cycle Count Registers. */
> +#define RM3100_REG_CC_X			0x05
> +#define RM3100_REG_CC_Y			0x07
> +#define RM3100_REG_CC_Z			0x09
> +
> +/* Poll Measurement Mode register. */
> +#define RM3100_REG_POLL			0x00
> +#define		RM3100_POLL_X		BIT(4)
> +#define		RM3100_POLL_Y		BIT(5)
> +#define		RM3100_POLL_Z		BIT(6)
> +
> +/* Continuous Measurement Mode register. */
> +#define RM3100_REG_CMM			0x01
> +#define		RM3100_CMM_START	BIT(0)
> +#define		RM3100_CMM_X		BIT(4)
> +#define		RM3100_CMM_Y		BIT(5)
> +#define		RM3100_CMM_Z		BIT(6)
> +
> +/* TiMe Rate Configuration register. */
> +#define RM3100_REG_TMRC			0x0B
> +#define RM3100_TMRC_OFFSET		0x92
> +
> +/* Result Status register. */
> +#define RM3100_REG_STATUS		0x34
> +#define		RM3100_STATUS_DRDY	BIT(7)
> +
> +/* Measurement result registers. */
> +#define RM3100_REG_MX2			0x24
> +#define RM3100_REG_MY2			0x27
> +#define RM3100_REG_MZ2			0x2a
> +
> +#define RM3100_W_REG_START		RM3100_REG_POLL
> +#define RM3100_W_REG_END		RM3100_REG_TMRC
> +#define RM3100_R_REG_START		RM3100_REG_POLL
> +#define RM3100_R_REG_END		RM3100_REG_STATUS
> +#define RM3100_V_REG_START		RM3100_REG_POLL
> +#define RM3100_V_REG_END		RM3100_REG_STATUS
> +
> +/*
> + * This is computed by hand, is the sum of channel storage bits and padding
> + * bits, which is 4+4+4+12=24 in here.
> + */
> +#define RM3100_SCAN_BYTES		24
> +
> +#define RM3100_CMM_AXIS_SHIFT		4
> +
> +struct rm3100_data {
> +	struct regmap *regmap;
> +	struct completion measuring_done;
> +	bool use_interrupt;
> +	int conversion_time;
> +	int scale;
> +	u8 buffer[RM3100_SCAN_BYTES];
> +	struct iio_trigger *drdy_trig;
> +
> +	/*
> +	 * This lock is for protecting the consistency of series of i2c
> +	 * operations, that is, to make sure a measurement process will
> +	 * not be interrupted by a set frequency operation, which should
> +	 * be taken where a series of i2c operation starts, released where
> +	 * the operation ends.
> +	 */
> +	struct mutex lock;
> +};
> +
> +static const struct regmap_range rm3100_readable_ranges[] = {
> +	regmap_reg_range(RM3100_R_REG_START, RM3100_R_REG_END),
> +};
> +
> +const struct regmap_access_table rm3100_readable_table = {
> +	.yes_ranges = rm3100_readable_ranges,
> +	.n_yes_ranges = ARRAY_SIZE(rm3100_readable_ranges),
> +};
> +EXPORT_SYMBOL_GPL(rm3100_readable_table);
> +
> +static const struct regmap_range rm3100_writable_ranges[] = {
> +	regmap_reg_range(RM3100_W_REG_START, RM3100_W_REG_END),
> +};
> +
> +const struct regmap_access_table rm3100_writable_table = {
> +	.yes_ranges = rm3100_writable_ranges,
> +	.n_yes_ranges = ARRAY_SIZE(rm3100_writable_ranges),
> +};
> +EXPORT_SYMBOL_GPL(rm3100_writable_table);
> +
> +static const struct regmap_range rm3100_volatile_ranges[] = {
> +	regmap_reg_range(RM3100_V_REG_START, RM3100_V_REG_END),
> +};
> +
> +const struct regmap_access_table rm3100_volatile_table = {
> +	.yes_ranges = rm3100_volatile_ranges,
> +	.n_yes_ranges = ARRAY_SIZE(rm3100_volatile_ranges),
> +};
> +EXPORT_SYMBOL_GPL(rm3100_volatile_table);
> +
> +static irqreturn_t rm3100_thread_fn(int irq, void *d)
> +{
> +	struct iio_dev *indio_dev = d;
> +	struct rm3100_data *data = iio_priv(indio_dev);
> +
> +	/*
> +	 * Write operation to any register or read operation
> +	 * to first byte of results will clear the interrupt.
> +	 */
> +	regmap_write(data->regmap, RM3100_REG_POLL, 0);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static irqreturn_t rm3100_irq_handler(int irq, void *d)
> +{
> +	struct iio_dev *indio_dev = d;
> +	struct rm3100_data *data = iio_priv(indio_dev);
> +
> +	switch (indio_dev->currentmode) {
> +	case INDIO_DIRECT_MODE:
> +		complete(&data->measuring_done);
> +		break;
> +	case INDIO_BUFFER_TRIGGERED:
> +		iio_trigger_poll(data->drdy_trig);
> +		break;
> +	default:
> +		dev_err(indio_dev->dev.parent,
> +			"device mode out of control, current mode: %d",
> +			indio_dev->currentmode);
> +	}
> +
> +	return IRQ_WAKE_THREAD;
> +}
> +
> +static int rm3100_wait_measurement(struct rm3100_data *data)
> +{
> +	struct regmap *regmap = data->regmap;
> +	unsigned int val;
> +	int tries = 20;
> +	int ret;
> +
> +	/*
> +	 * A read cycle of 400kbits i2c bus is about 20us, plus the time
> +	 * used for scheduling, a read cycle of fast mode of this device
> +	 * can reach 1.7ms, it may be possible for data to arrive just
> +	 * after we check the RM3100_REG_STATUS. In this case, irq_handler is
> +	 * called before measuring_done is reinitialized, it will wait
> +	 * forever for data that has already been ready.
> +	 * Reinitialize measuring_done before looking up makes sure we
> +	 * will always capture interrupt no matter when it happens.
> +	 */
> +	if (data->use_interrupt)
> +		reinit_completion(&data->measuring_done);
> +
> +	ret = regmap_read(regmap, RM3100_REG_STATUS, &val);
> +	if (ret < 0)
> +		return ret;
> +
> +	if ((val & RM3100_STATUS_DRDY) != RM3100_STATUS_DRDY) {
> +		if (data->use_interrupt) {
> +			ret = wait_for_completion_timeout(&data->measuring_done,
> +				msecs_to_jiffies(data->conversion_time));
> +			if (!ret)
> +				return -ETIMEDOUT;
> +		} else {
> +			do {
> +				usleep_range(1000, 5000);
> +
> +				ret = regmap_read(regmap, RM3100_REG_STATUS,
> +						  &val);
> +				if (ret < 0)
> +					return ret;
> +
> +				if (val & RM3100_STATUS_DRDY)
> +					break;
> +			} while (--tries);
> +			if (!tries)
> +				return -ETIMEDOUT;
> +		}
> +	}
> +	return 0;
> +}
> +
> +static int rm3100_read_mag(struct rm3100_data *data, int idx, int *val)
> +{
> +	struct regmap *regmap = data->regmap;
> +	u8 buffer[3];
> +	int ret;
> +
> +	mutex_lock(&data->lock);
> +	ret = regmap_write(regmap, RM3100_REG_POLL, BIT(4 + idx));
> +	if (ret < 0)
> +		goto unlock_return;
> +
> +	ret = rm3100_wait_measurement(data);
> +	if (ret < 0)
> +		goto unlock_return;
> +
> +	ret = regmap_bulk_read(regmap, RM3100_REG_MX2 + 3 * idx, buffer, 3);
> +	if (ret < 0)
> +		goto unlock_return;
> +	mutex_unlock(&data->lock);
> +
> +	*val = sign_extend32((buffer[0] << 16) | (buffer[1] << 8) | buffer[2],
> +			     23);
> +
> +	return IIO_VAL_INT;
> +
> +unlock_return:
> +	mutex_unlock(&data->lock);
> +	return ret;
> +}
> +
> +#define RM3100_CHANNEL(axis, idx)					\
> +	{								\
> +		.type = IIO_MAGN,					\
> +		.modified = 1,						\
> +		.channel2 = IIO_MOD_##axis,				\
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
> +		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) |	\
> +			BIT(IIO_CHAN_INFO_SAMP_FREQ),			\
> +		.scan_index = idx,					\
> +		.scan_type = {						\
> +			.sign = 's',					\
> +			.realbits = 24,					\
> +			.storagebits = 32,				\
> +			.shift = 8,					\
> +			.endianness = IIO_BE,				\
> +		},							\
> +	}
> +
> +static const struct iio_chan_spec rm3100_channels[] = {
> +	RM3100_CHANNEL(X, 0),
> +	RM3100_CHANNEL(Y, 1),
> +	RM3100_CHANNEL(Z, 2),
> +	IIO_CHAN_SOFT_TIMESTAMP(3),
> +};
> +
> +static IIO_CONST_ATTR_SAMP_FREQ_AVAIL(
> +	"600 300 150 75 37 18 9 4.5 2.3 1.2 0.6 0.3 0.015 0.075"
> +);
> +
> +static struct attribute *rm3100_attributes[] = {
> +	&iio_const_attr_sampling_frequency_available.dev_attr.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group rm3100_attribute_group = {
> +	.attrs = rm3100_attributes,
> +};
> +
> +#define RM3100_SAMP_NUM			14
> +
> +/*
> + * Frequency : rm3100_samp_rates[][0].rm3100_samp_rates[][1]Hz.
> + * Time between reading: rm3100_sam_rates[][2]ms.
> + * The first one is actually 1.7ms.
> + */
> +static const int rm3100_samp_rates[RM3100_SAMP_NUM][3] = {
> +	{600, 0, 2}, {300, 0, 3}, {150, 0, 7}, {75, 0, 13}, {37, 0, 27},
> +	{18, 0, 55}, {9, 0, 110}, {4, 500000, 220}, {2, 300000, 440},
> +	{1, 200000, 800}, {0, 600000, 1600}, {0, 300000, 3300},
> +	{0, 15000, 6700},  {0, 75000, 13000}
> +};
> +
> +static int rm3100_get_samp_freq(struct rm3100_data *data, int *val, int *val2)
> +{
> +	unsigned int tmp;
> +	int ret;
> +
> +	mutex_lock(&data->lock);
> +	ret = regmap_read(data->regmap, RM3100_REG_TMRC, &tmp);
> +	mutex_unlock(&data->lock);
> +	if (ret < 0)
> +		return ret;
> +	*val = rm3100_samp_rates[tmp - RM3100_TMRC_OFFSET][0];
> +	*val2 = rm3100_samp_rates[tmp - RM3100_TMRC_OFFSET][1];
> +
> +	return IIO_VAL_INT_PLUS_MICRO;
> +}
> +
> +static int rm3100_set_cycle_count(struct rm3100_data *data, int val)
> +{
> +	int ret;
> +	u8 i;
> +
> +	for (i = 0; i < 3; i++) {
> +		ret = regmap_write(data->regmap, RM3100_REG_CC_X + 2 * i, val);
> +		if (ret < 0)
> +			return ret;
> +	}
> +
> +	/*
> +	 * The scale of this sensor depends on the cycle count value, these
> +	 * three values are corresponding to the cycle count value 50, 100,
> +	 * 200. scale = output / gain * 10^4.
> +	 */
> +	switch (val) {
> +	case 50:
> +		data->scale = 500;
> +		break;
> +	case 100:
> +		data->scale = 263;
> +		break;
> +	/*
> +	 * case 200:
> +	 * This function will never be called by users' code, so here we
> +	 * assume that it will never get a wrong parameter.
> +	 */
> +	default:
> +		data->scale = 133;
> +	}
> +
> +	return 0;
> +}
> +
> +static int rm3100_set_samp_freq(struct iio_dev *indio_dev, int val, int val2)
> +{
> +	struct rm3100_data *data = iio_priv(indio_dev);
> +	struct regmap *regmap = data->regmap;
> +	unsigned int cycle_count;
> +	int ret;
> +	int i;
> +
> +	mutex_lock(&data->lock);
> +	/* All cycle count registers use the same value. */
> +	ret = regmap_read(regmap, RM3100_REG_CC_X, &cycle_count);
> +	if (ret < 0)
> +		goto unlock_return;
> +
> +	for (i = 0; i < RM3100_SAMP_NUM; i++) {
> +		if (val == rm3100_samp_rates[i][0] &&
> +		    val2 == rm3100_samp_rates[i][1])
> +			break;
> +	}
> +	if (i == RM3100_SAMP_NUM) {
> +		ret = -EINVAL;
> +		goto unlock_return;
> +	}
> +
> +	ret = regmap_write(regmap, RM3100_REG_TMRC, i + RM3100_TMRC_OFFSET);
> +	if (ret < 0)
> +		goto unlock_return;
> +
> +	/* Checking if cycle count registers need changing. */
> +	if (val == 600 && cycle_count == 200) {
> +		ret = rm3100_set_cycle_count(data, 100);
> +		if (ret < 0)
> +			goto unlock_return;
> +	} else if (val != 600 && cycle_count == 100) {
> +		ret = rm3100_set_cycle_count(data, 200);
> +		if (ret < 0)
> +			goto unlock_return;
> +	}
> +
> +	if (indio_dev->currentmode == INDIO_BUFFER_TRIGGERED) {
> +		/* Writing TMRC registers requires CMM reset. */
> +		ret = regmap_write(regmap, RM3100_REG_CMM, 0);
> +		if (ret < 0)
> +			goto unlock_return;
> +		ret = regmap_write(data->regmap, RM3100_REG_CMM,
> +		(*indio_dev->active_scan_mask & 0x7) << RM3100_CMM_AXIS_SHIFT |
> +		RM3100_CMM_START);
These should be indented one more tab.

> +		if (ret < 0)
> +			goto unlock_return;
> +	}
> +	mutex_unlock(&data->lock);
> +
> +	data->conversion_time = rm3100_samp_rates[i][2] * 2;
> +	return 0;
> +
> +unlock_return:
> +	mutex_unlock(&data->lock);
> +	return ret;
> +}
> +
> +static int rm3100_read_raw(struct iio_dev *indio_dev,
> +			   const struct iio_chan_spec *chan,
> +			   int *val, int *val2, long mask)
> +{
> +	struct rm3100_data *data = iio_priv(indio_dev);
> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		ret = iio_device_claim_direct_mode(indio_dev);
> +		if (ret < 0)
> +			return ret;
> +
> +		ret = rm3100_read_mag(data, chan->scan_index, val);
> +		iio_device_release_direct_mode(indio_dev);
> +
> +		return ret;
> +	case IIO_CHAN_INFO_SCALE:
> +		*val = 0;
> +		*val2 = data->scale;
> +
> +		return IIO_VAL_INT_PLUS_MICRO;
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		return rm3100_get_samp_freq(data, val, val2);
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static int rm3100_write_raw(struct iio_dev *indio_dev,
> +			    struct iio_chan_spec const *chan,
> +			    int val, int val2, long mask)
> +{
> +	switch (mask) {
> +	case IIO_CHAN_INFO_SAMP_FREQ:
> +		return rm3100_set_samp_freq(indio_dev, val, val2);
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
> +static const struct iio_info rm3100_info = {
> +	.attrs = &rm3100_attribute_group,
> +	.read_raw = rm3100_read_raw,
> +	.write_raw = rm3100_write_raw,
> +};
> +
> +static int rm3100_buffer_preenable(struct iio_dev *indio_dev)
> +{
> +	struct rm3100_data *data = iio_priv(indio_dev);
> +
> +	/* Starting channels enabled. */
> +	return regmap_write(data->regmap, RM3100_REG_CMM,
> +		(*indio_dev->active_scan_mask & 0x7) << RM3100_CMM_AXIS_SHIFT |
> +		RM3100_CMM_START);
> +}
> +
> +static int rm3100_buffer_postdisable(struct iio_dev *indio_dev)
> +{
> +	struct rm3100_data *data = iio_priv(indio_dev);
> +
> +	return regmap_write(data->regmap, RM3100_REG_CMM, 0);
> +}
> +
> +static const struct iio_buffer_setup_ops rm3100_buffer_ops = {
> +	.preenable = rm3100_buffer_preenable,
> +	.postenable = iio_triggered_buffer_postenable,
> +	.predisable = iio_triggered_buffer_predisable,
> +	.postdisable = rm3100_buffer_postdisable,
> +};
> +
> +static irqreturn_t rm3100_trigger_handler(int irq, void *p)
> +{
> +	struct iio_poll_func *pf = p;
> +	struct iio_dev *indio_dev = pf->indio_dev;
> +	unsigned long scan_mask = *indio_dev->active_scan_mask;
> +	unsigned int mask_len = indio_dev->masklength;
> +	struct rm3100_data *data = iio_priv(indio_dev);
> +	struct regmap *regmap = data->regmap;
> +	int ret, i, bit;
> +
> +	mutex_lock(&data->lock);
> +	switch (scan_mask) {
> +	case BIT(0) | BIT(1) | BIT(2):
> +	case BIT(0) | BIT(2):
> +		ret = regmap_bulk_read(regmap, RM3100_REG_MX2, data->buffer, 9);
I could be going crazy but...

This results in x and z being read and...

> +		mutex_unlock(&data->lock);
> +		if (ret < 0)
> +			goto done;
> +	break;
> +	case BIT(0) | BIT(1):
> +		ret = regmap_bulk_read(regmap, RM3100_REG_MX2, data->buffer, 6);
> +		mutex_unlock(&data->lock);
> +		if (ret < 0)
> +			goto done;
> +	break;
> +	case BIT(1) | BIT(2):
> +		ret = regmap_bulk_read(regmap, RM3100_REG_MY2, data->buffer, 6);
> +		mutex_unlock(&data->lock);
> +		if (ret < 0)
> +			goto done;
> +	break;
> +	default:
> +		for_each_set_bit(bit, &scan_mask, mask_len) {
> +			ret = regmap_bulk_read(regmap, RM3100_REG_MX2 + 3 * bit,
> +					       data->buffer + bit * 3, 3);
> +			if (ret < 0) {
> +				mutex_unlock(&data->lock);
> +				goto done;
> +			}
> +		}
> +		mutex_unlock(&data->lock);
> +	}
> +
> +	/* Convert XXXYYYZZZxxx to XXXxYYYxZZZx. x for paddings. */
> +	for (i = mask_len - 1; i > 0; i--)
> +		if (scan_mask | BIT(i))
> +			memcpy(data->buffer + i * 4, data->buffer + i * 3, 3);
... shuffles them to be correctly aligned, but not as
XXXxZZZx but rather XXXxxxxxZZZx which is not where we expect them to be.
Now if you had provided available_scan_masks you could actually drop
the explicit handling of BIT(0) | BIT(2) but then you'd end up shifting
data that you didn't care about (probably not too bad).

Idle thought, I wonder if it's cheaper not to check the scan_mask and just
shuffle stuff that might not be used..  Those conditionals are pricey but
the memcpy may or may not have some as well depending on how clever the
compiler is being.

> +
> +	/*
> +	 * Always using the same buffer so that we wouldn't need to set the
> +	 * paddings to 0 in case of leaking any data.
> +	 */
> +	iio_push_to_buffers_with_timestamp(indio_dev, data->buffer,
> +					   pf->timestamp);
> +
> +done:
> +	iio_trigger_notify_done(indio_dev->trig);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +int rm3100_common_probe(struct device *dev, struct regmap *regmap, int irq)
> +{
> +	struct iio_dev *indio_dev;
> +	struct rm3100_data *data;
> +	unsigned int tmp;
> +	int ret;
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	data = iio_priv(indio_dev);
> +	data->regmap = regmap;
> +
> +	mutex_init(&data->lock);
> +
> +	indio_dev->dev.parent = dev;
> +	indio_dev->name = "rm3100";
> +	indio_dev->info = &rm3100_info;
> +	indio_dev->channels = rm3100_channels;
> +	indio_dev->num_channels = ARRAY_SIZE(rm3100_channels);
> +	indio_dev->modes = INDIO_DIRECT_MODE | INDIO_BUFFER_TRIGGERED;
> +	indio_dev->currentmode = INDIO_DIRECT_MODE;

Huh. That's an interesting one... Looks like a bug in the core to me that
somehow has never bitten us as no driver has ever done anything other
than explicitly match against other modes.  No one sets currentmode
directly so we should be good just putting this in the core as long
as a device supports direct mode.  I'll look at that when I get a moment.

> +
> +	if (!irq)
> +		data->use_interrupt = false;
> +	else {
> +		data->use_interrupt = true;
> +
> +		ret = devm_request_threaded_irq(dev,
> +						irq,
> +						rm3100_irq_handler,
> +						rm3100_thread_fn,
> +						IRQF_TRIGGER_HIGH |
> +						IRQF_ONESHOT,
> +						indio_dev->name,
> +						indio_dev);
> +		if (ret < 0) {
> +			dev_err(dev, "request irq line failed.\n");
> +			return ret;
> +		}
> +		init_completion(&data->measuring_done);
> +
> +		data->drdy_trig = devm_iio_trigger_alloc(dev, "%s-drdy%d",
> +							 indio_dev->name,
> +							 indio_dev->id);
> +		if (!data->drdy_trig)
> +			return -ENOMEM;
> +
> +		data->drdy_trig->dev.parent = dev;
> +		ret = devm_iio_trigger_register(dev, data->drdy_trig);
> +		if (ret < 0)
> +			return ret;
> +	}
> +
> +	ret = devm_iio_triggered_buffer_setup(dev, indio_dev,
> +					      &iio_pollfunc_store_time,
> +					      rm3100_trigger_handler,
> +					      &rm3100_buffer_ops);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = regmap_read(regmap, RM3100_REG_TMRC, &tmp);
> +	if (ret < 0)
> +		return ret;
> +	/* Initializing max wait time, which is double conversion time. */
> +	data->conversion_time = rm3100_samp_rates[tmp - RM3100_TMRC_OFFSET][2]
> +				* 2;
> +
> +	/* Cycle count values may not be what we want. */
> +	if ((tmp - RM3100_TMRC_OFFSET) == 0)
> +		rm3100_set_cycle_count(data, 100);
> +	else
> +		rm3100_set_cycle_count(data, 200);
> +
> +	return devm_iio_device_register(dev, indio_dev);
> +}
> +EXPORT_SYMBOL_GPL(rm3100_common_probe);
> +
> +MODULE_AUTHOR("Song Qiang <songqiang1304521@gmail.com>");
> +MODULE_DESCRIPTION("PNI RM3100 3-axis magnetometer i2c driver");
> +MODULE_LICENSE("GPL v2");
> diff --git a/drivers/iio/magnetometer/rm3100-i2c.c b/drivers/iio/magnetometer/rm3100-i2c.c
> new file mode 100644
> index 000000000000..a3b2ae4fb53d
> --- /dev/null
> +++ b/drivers/iio/magnetometer/rm3100-i2c.c
> @@ -0,0 +1,54 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Support for PNI RM3100 3-axis geomagnetic sensor on a i2c bus.
> + *
> + * Copyright (C) 2018 Song Qiang <songqiang1304521@gmail.com>
> + *
> + * i2c slave address: 0x20 + SA1 << 1 + SA0.
> + */
> +
> +#include <linux/i2c.h>
> +#include <linux/module.h>
> +
> +#include "rm3100.h"
> +
> +static const struct regmap_config rm3100_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +
> +	.rd_table = &rm3100_readable_table,
> +	.wr_table = &rm3100_writable_table,
> +	.volatile_table = &rm3100_volatile_table,
> +
> +	.cache_type = REGCACHE_RBTREE,
> +};
> +
> +static int rm3100_probe(struct i2c_client *client)
> +{
> +	struct regmap *regmap;
> +
> +	regmap =  devm_regmap_init_i2c(client, &rm3100_regmap_config);

Extra space before devm.

> +	if (IS_ERR(regmap))
> +		return PTR_ERR(regmap);
> +
> +	return rm3100_common_probe(&client->dev, regmap, client->irq);
> +}
> +
> +static const struct of_device_id rm3100_dt_match[] = {
> +	{ .compatible = "pni,rm3100", },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, rm3100_dt_match);
> +
> +static struct i2c_driver rm3100_driver = {
> +	.driver = {
> +		.name = "rm3100-i2c",
> +		.of_match_table = rm3100_dt_match,
> +	},
> +	.probe_new = rm3100_probe,
> +};
> +module_i2c_driver(rm3100_driver);
> +
> +MODULE_AUTHOR("Song Qiang <songqiang1304521@gmail.com>");
> +MODULE_DESCRIPTION("PNI RM3100 3-axis magnetometer i2c driver");
> +MODULE_LICENSE("GPL v2");
> diff --git a/drivers/iio/magnetometer/rm3100-spi.c b/drivers/iio/magnetometer/rm3100-spi.c
> new file mode 100644
> index 000000000000..65d5eb9e4f5e
> --- /dev/null
> +++ b/drivers/iio/magnetometer/rm3100-spi.c
> @@ -0,0 +1,64 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Support for PNI RM3100 3-axis geomagnetic sensor on a spi bus.
> + *
> + * Copyright (C) 2018 Song Qiang <songqiang1304521@gmail.com>
> + */
> +
> +#include <linux/module.h>
> +#include <linux/spi/spi.h>
> +
> +#include "rm3100.h"
> +
> +static const struct regmap_config rm3100_regmap_config = {
> +	.reg_bits = 8,
> +	.val_bits = 8,
> +
> +	.rd_table = &rm3100_readable_table,
> +	.wr_table = &rm3100_writable_table,
> +	.volatile_table = &rm3100_volatile_table,
> +
> +	.read_flag_mask = 0x80,
> +
> +	.cache_type = REGCACHE_RBTREE,
> +};
> +
> +static int rm3100_probe(struct spi_device *spi)
> +{
> +	struct regmap *regmap;
> +	int ret;
> +
> +	/* Actually this device supports both mode 0 and mode 3. */
> +	spi->mode = SPI_MODE_0;
> +	/* Data rates cannot exceed 1Mbits. */
> +	spi->max_speed_hz = 1000000;
> +	spi->bits_per_word = 8;
> +	ret = spi_setup(spi);
> +	if (ret)
> +		return ret;
> +
> +	regmap = devm_regmap_init_spi(spi, &rm3100_regmap_config);
> +	if (IS_ERR(regmap))
> +		return PTR_ERR(regmap);
> +
> +	return rm3100_common_probe(&spi->dev, regmap, spi->irq);
> +}
> +
> +static const struct of_device_id rm3100_dt_match[] = {
> +	{ .compatible = "pni,rm3100", },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, rm3100_dt_match);
> +
> +static struct spi_driver rm3100_driver = {
> +	.driver = {
> +		.name = "rm3100-spi",
> +		.of_match_table = rm3100_dt_match,
> +	},
> +	.probe = rm3100_probe,
> +};
> +module_spi_driver(rm3100_driver);
> +
> +MODULE_AUTHOR("Song Qiang <songqiang1304521@gmail.com>");
> +MODULE_DESCRIPTION("PNI RM3100 3-axis magnetometer spi driver");
> +MODULE_LICENSE("GPL v2");
> diff --git a/drivers/iio/magnetometer/rm3100.h b/drivers/iio/magnetometer/rm3100.h
> new file mode 100644
> index 000000000000..c3508218bc77
> --- /dev/null
> +++ b/drivers/iio/magnetometer/rm3100.h
> @@ -0,0 +1,17 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2018 Song Qiang <songqiang1304521@gmail.com>
> + */
> +
> +#ifndef RM3100_CORE_H
> +#define RM3100_CORE_H
> +
> +#include <linux/regmap.h>
> +
> +extern const struct regmap_access_table rm3100_readable_table;
> +extern const struct regmap_access_table rm3100_writable_table;
> +extern const struct regmap_access_table rm3100_volatile_table;
> +
> +int rm3100_common_probe(struct device *dev, struct regmap *regmap, int irq);
> +
> +#endif /* RM3100_CORE_H */