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Subject: Re: [v3 1/2] iio: gyro: Add driver support for ADXRS290
To:     Jonathan Cameron <jic23@kernel.org>
Cc:     dragos.bogdan@analog.com, darius.berghe@analog.com,
        linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org
References: <20200724110159.24402-1-nish.malpani25@gmail.com>
 <20200726131549.02a28962@archlinux>
From:   Nishant Malpani <nish.malpani25@gmail.com>
Message-ID: <512ff7ea-76db-5a20-29ee-e48e28779b6d@gmail.com>
Date:   Sun, 26 Jul 2020 19:35:55 +0530
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On 26/07/20 5:45 pm, Jonathan Cameron wrote:
> On Fri, 24 Jul 2020 16:31:59 +0530
> Nishant Malpani <nish.malpani25@gmail.com> wrote:
> 
>> ADXRS290 is a high performance MEMS pitch and roll (dual-axis in-plane)
>> angular rate sensor (gyroscope) designed for use in stabilization
>> applications. It also features an internal temperature sensor and
>> programmable high-pass and low-pass filters.
>>
>> Add support for ADXRS290 in direct-access mode for now.
>>
>> Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/ADXRS290.pdf
>> Signed-off-by: Nishant Malpani <nish.malpani25@gmail.com>
> 
> Looks pretty good to me.  A few minor comments seeing as you'll be doing
> a v4 anyway to tidy up the bits Andy pointed out.
> 
> I've pointed out the locking is probably in excess of what is needed, but
> I have no problem with you leaving it as it stands, in the interests of
> having less fragile code as you extend the driver futher.
> 
> Thanks,
> 
> Jonathan
> 
>> ---
>>
>> Changes in v3:
>>    - drop "Link" tag & extra line in commit message
>>    - rename cut-off frequencies tables to
>>      'adxrs290_{lpf, hpf}_3db_freq_hz_table' to be more descriptive
>>    - fix unsigned type errors
>>    - add comments on how to scale raw angular velocity and temperature
>>      values to appropriate units mentioned in the ABI
>>    - re-order declarations in reversed spruce tree order
>>    - remove 'indio_dev->dev.parent = &spi->dev' as the iio core handles it
>>      during iio_device_alloc()
>>    - use plain msleep() instead of the interruptible variant
>>    - remove extra terminal comma
>>
>> Changes in v2:
>>    - append copyright tag with author's info
>>    - remove asm/unaligned.h header
>>    - remove unnecessary comments about the registers' description
>>    - rephrase comment on the usage of mutex_lock
>>    - discard the usage of local tx, rx buffers; use DMA-safe buffers
>>      provided by the SPI core instead
>>    - utilize spi_w8r16 provided by the SPI core instead of writing a
>>      wrapper over spi_sync_transfer which semantically does the same
>>    - equip spi_write_then_read instead of plain spi_write since the
>>      latter requires a DMA-safe buffer
>>    - implement exact matching of filter 3db frequencies instead of
>>      finding the "closest" match; rounding complexity is left to the
>>      userspace
>>    - include 'info_mask_shared_by_type_available' when initialising
>>      iio_chan_spec instead of explicitly exposing attributes
>>      signifying available filter 3db frequencies; with this we can
>>      utilize read_avail core callback
>> ---
>>   MAINTAINERS                 |   6 +
>>   drivers/iio/gyro/Kconfig    |  10 +
>>   drivers/iio/gyro/Makefile   |   1 +
>>   drivers/iio/gyro/adxrs290.c | 446 ++++++++++++++++++++++++++++++++++++
>>   4 files changed, 463 insertions(+)
>>   create mode 100644 drivers/iio/gyro/adxrs290.c
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 9077411c9890..71ae9b184179 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -1098,6 +1098,12 @@ L:	linux-media@vger.kernel.org
>>   S:	Maintained
>>   F:	drivers/media/i2c/adv7842*
>>   
>> +ANALOG DEVICES INC ADXRS290 DRIVER
>> +M:	Nishant Malpani <nish.malpani25@gmail.com>
>> +L:	linux-iio@vger.kernel.org
>> +S:	Supported
>> +F:	drivers/iio/gyro/adxrs290.c
>> +
>>   ANALOG DEVICES INC ASOC CODEC DRIVERS
>>   M:	Lars-Peter Clausen <lars@metafoo.de>
>>   M:	Nuno Sá <nuno.sa@analog.com>
>> diff --git a/drivers/iio/gyro/Kconfig b/drivers/iio/gyro/Kconfig
>> index 6daeddf37f60..024a34139875 100644
>> --- a/drivers/iio/gyro/Kconfig
>> +++ b/drivers/iio/gyro/Kconfig
>> @@ -41,6 +41,16 @@ config ADIS16260
>>   	  This driver can also be built as a module.  If so, the module
>>   	  will be called adis16260.
>>   
>> +config ADXRS290
>> +	tristate "Analog Devices ADXRS290 Dual-Axis MEMS Gyroscope SPI driver"
>> +	depends on SPI
>> +	help
>> +	  Say yes here to build support for Analog Devices ADXRS290 programmable
>> +	  digital output gyroscope.
>> +
>> +	  This driver can also be built as a module. If so, the module will be
>> +	  called adxrs290.
>> +
>>   config ADXRS450
>>   	tristate "Analog Devices ADXRS450/3 Digital Output Gyroscope SPI driver"
>>   	depends on SPI
>> diff --git a/drivers/iio/gyro/Makefile b/drivers/iio/gyro/Makefile
>> index 45cbd5dc644e..0319b397dc3f 100644
>> --- a/drivers/iio/gyro/Makefile
>> +++ b/drivers/iio/gyro/Makefile
>> @@ -8,6 +8,7 @@ obj-$(CONFIG_ADIS16080) += adis16080.o
>>   obj-$(CONFIG_ADIS16130) += adis16130.o
>>   obj-$(CONFIG_ADIS16136) += adis16136.o
>>   obj-$(CONFIG_ADIS16260) += adis16260.o
>> +obj-$(CONFIG_ADXRS290) += adxrs290.o
>>   obj-$(CONFIG_ADXRS450) += adxrs450.o
>>   obj-$(CONFIG_BMG160) += bmg160_core.o
>>   obj-$(CONFIG_BMG160_I2C) += bmg160_i2c.o
>> diff --git a/drivers/iio/gyro/adxrs290.c b/drivers/iio/gyro/adxrs290.c
>> new file mode 100644
>> index 000000000000..cff1af9211bc
>> --- /dev/null
>> +++ b/drivers/iio/gyro/adxrs290.c
>> @@ -0,0 +1,446 @@
>> +// SPDX-License-Identifier: GPL-2.0-or-later
>> +/*
>> + * ADXRS290 SPI Gyroscope Driver
>> + *
>> + * Copyright (C) 2020 Nishant Malpani <nish.malpani25@gmail.com>
>> + * Copyright (C) 2020 Analog Devices, Inc.
>> + */
>> +
>> +#include <linux/bitfield.h>
>> +#include <linux/device.h>
>> +#include <linux/delay.h>
>> +#include <linux/kernel.h>
>> +#include <linux/module.h>
>> +#include <linux/spi/spi.h>
>> +
>> +#include <linux/iio/iio.h>
>> +#include <linux/iio/sysfs.h>
>> +
>> +#define ADXRS290_ADI_ID		0xAD
>> +#define ADXRS290_MEMS_ID	0x1D
>> +#define ADXRS290_DEV_ID		0x92
>> +
>> +#define ADXRS290_REG_ADI_ID	0x00
>> +#define ADXRS290_REG_MEMS_ID	0x01
>> +#define ADXRS290_REG_DEV_ID	0x02
>> +#define ADXRS290_REG_REV_ID	0x03
>> +#define ADXRS290_REG_SN0	0x04 /* Serial Number Registers, 4 bytes */
>> +#define ADXRS290_REG_DATAX0	0x08 /* Roll Rate o/p Data Regs, 2 bytes */
>> +#define ADXRS290_REG_DATAY0	0x0A /* Pitch Rate o/p Data Regs, 2 bytes */
>> +#define ADXRS290_REG_TEMP0	0x0C
>> +#define ADXRS290_REG_POWER_CTL	0x10
>> +#define ADXRS290_REG_FILTER	0x11
>> +#define ADXRS290_REG_DATA_RDY	0x12
>> +
>> +#define ADXRS290_READ		BIT(7)
>> +#define ADXRS290_TSM		BIT(0)
>> +#define ADXRS290_MEASUREMENT	BIT(1)
>> +#define ADXRS290_SYNC		GENMASK(1, 0)
>> +#define ADXRS290_LPF_MASK	GENMASK(2, 0)
>> +#define ADXRS290_LPF(x)		FIELD_PREP(ADXRS290_LPF_MASK, x)
>> +#define ADXRS290_HPF_MASK	GENMASK(7, 4)
>> +#define ADXRS290_HPF(x)		FIELD_PREP(ADXRS290_HPF_MASK, x)
>> +
>> +#define ADXRS290_READ_REG(reg)	(ADXRS290_READ | (reg))
>> +
>> +#define ADXRS290_MAX_TRANSITION_TIME_MS 100
>> +
>> +enum adxrs290_mode {
>> +	STANDBY,
>> +	MEASUREMENT,
>> +};
>> +
>> +struct adxrs290_state {
>> +	struct spi_device	*spi;
>> +	/* Serialize reads and their subsequent processing */
>> +	struct mutex		lock;
>> +	enum adxrs290_mode	mode;
>> +	unsigned int		lpf_3db_freq_idx;
>> +	unsigned int		hpf_3db_freq_idx;
>> +};
>> +
>> +/*
>> + * Available cut-off frequencies of the low pass filter in Hz.
>> + * The integer part and fractional part are represented separately.
>> + */
>> +static const int adxrs290_lpf_3db_freq_hz_table[][2] = {
>> +	[0] = {480, 0},
>> +	[1] = {320, 0},
>> +	[2] = {160, 0},
>> +	[3] = {80, 0},
>> +	[4] = {56, 600000},
>> +	[5] = {40, 0},
>> +	[6] = {28, 300000},
>> +	[7] = {20, 0},
>> +};
>> +
>> +/*
>> + * Available cut-off frequencies of the high pass filter in Hz.
>> + * The integer part and fractional part are represented separately.
>> + */
>> +static const int adxrs290_hpf_3db_freq_hz_table[][2] = {
>> +	[0] = {0, 0},
>> +	[1] = {0, 11000},
>> +	[2] = {0, 22000},
>> +	[3] = {0, 44000},
>> +	[4] = {0, 87000},
>> +	[5] = {0, 175000},
>> +	[6] = {0, 350000},
>> +	[7] = {0, 700000},
>> +	[8] = {1, 400000},
>> +	[9] = {2, 800000},
>> +	[10] = {11, 300000},
>> +};
>> +
>> +static int adxrs290_get_rate_data(struct iio_dev *indio_dev, const u8 cmd,
>> +				  unsigned int *val)
> 
> Why go through the effort of signed to unsigned to signed for val?
>
Yeah, those are some unnecessary type promotions and demotions. Will 
change the function signature to directly accept 'int *val' in v4.

>> +{
>> +	struct adxrs290_state *st = iio_priv(indio_dev);
>> +	int ret = 0;
>> +	int temp;
>> +
>> +	mutex_lock(&st->lock);
>> +	temp = spi_w8r16(st->spi, cmd);
>> +	if (temp < 0) {
>> +		ret = temp;
>> +		goto err_unlock;
>> +	}
>> +
>> +	*val = temp;
>> +
>> +err_unlock:
>> +	mutex_unlock(&st->lock);
>> +	return ret;
>> +}
>> +
>> +static int adxrs290_get_temp_data(struct iio_dev *indio_dev, unsigned int *val)
>> +{
>> +	const u8 cmd = ADXRS290_READ_REG(ADXRS290_REG_TEMP0);
>> +	struct adxrs290_state *st = iio_priv(indio_dev);
>> +	int ret = 0;
>> +	int temp;
>> +
>> +	mutex_lock(&st->lock);
> 
> Just a quick note here.  I don't think you actually need the lock
> (yet) as you aren't doing any read modify write cycles and in this
> particular case there is no local cached state to protect.
> However, I don't mind if you want to leave them as it may make things
> less fragile as you move forwards.
> 
I was also doubtful about the protections previously but, as you've 
summarized perfectly, I left those as a 'good-to-have' for now, in the 
hope that they might be necessary as I incrementally add more support in 
the driver.

>> +	temp = spi_w8r16(st->spi, cmd);
>> +	if (temp < 0) {
>> +		ret = temp;
>> +		goto err_unlock;
>> +	}
>> +
>> +	/* extract lower 12 bits temperature reading */
>> +	*val = temp & 0x0FFF;
>> +
>> +err_unlock:
>> +	mutex_unlock(&st->lock);
>> +	return ret;
>> +}
>> +
>> +static int adxrs290_get_3db_freq(struct iio_dev *indio_dev, u8 *val, u8 *val2)
>> +{
>> +	const u8 cmd = ADXRS290_READ_REG(ADXRS290_REG_FILTER);
>> +	struct adxrs290_state *st = iio_priv(indio_dev);
>> +	int ret = 0;
>> +	short temp;
>> +
>> +	mutex_lock(&st->lock);
>> +	temp = spi_w8r8(st->spi, cmd);
>> +	if (temp < 0) {
>> +		ret = temp;
>> +		goto err_unlock;
>> +	}
>> +
>> +	*val = FIELD_GET(ADXRS290_LPF_MASK, temp);
>> +	*val2 = FIELD_GET(ADXRS290_HPF_MASK, temp);
>> +
>> +err_unlock:
>> +	mutex_unlock(&st->lock);
>> +	return ret;
>> +}
>> +
>> +static int adxrs290_spi_write_reg(struct spi_device *spi, const u8 reg,
>> +				  const u8 val)
>> +{
>> +	u8 buf[2];
>> +
>> +	buf[0] = reg;
>> +	buf[1] = val;
>> +
>> +	return spi_write_then_read(spi, buf, ARRAY_SIZE(buf), NULL, 0);
>> +}
>> +
>> +static int adxrs290_find_match(const int (*freq_tbl)[2], const int n,
>> +			       const int val, const int val2)
>> +{
>> +	int i;
>> +
>> +	for (i = 0; i < n; i++) {
>> +		if (freq_tbl[i][0] == val && freq_tbl[i][1] == val2)
>> +			return i;
>> +	}
>> +
>> +	return -EINVAL;
>> +}
>> +
>> +static int adxrs290_set_filter_freq(struct iio_dev *indio_dev,
>> +				    const unsigned int lpf_idx,
>> +				    const unsigned int hpf_idx)
>> +{
>> +	struct adxrs290_state *st = iio_priv(indio_dev);
>> +	u8 val;
>> +
>> +	val = ADXRS290_HPF(hpf_idx) | ADXRS290_LPF(lpf_idx);
>> +
>> +	return adxrs290_spi_write_reg(st->spi, ADXRS290_REG_FILTER, val);
>> +}
>> +
>> +static int adxrs290_initial_setup(struct iio_dev *indio_dev)
>> +{
>> +	struct adxrs290_state *st = iio_priv(indio_dev);
>> +
>> +	st->mode = MEASUREMENT;
>> +
>> +	return adxrs290_spi_write_reg(st->spi,
>> +				      ADXRS290_REG_POWER_CTL,
>> +				      ADXRS290_MEASUREMENT | ADXRS290_TSM);
>> +}
>> +
>> +static int adxrs290_read_raw(struct iio_dev *indio_dev,
>> +			     struct iio_chan_spec const *chan,
>> +			     int *val,
>> +			     int *val2,
>> +			     long mask)
>> +{
>> +	struct adxrs290_state *st = iio_priv(indio_dev);
>> +	unsigned int t;
>> +	int ret;
>> +
>> +	switch (mask) {
>> +	case IIO_CHAN_INFO_RAW:
>> +		switch (chan->type) {
>> +		case IIO_ANGL_VEL:
>> +			ret = adxrs290_get_rate_data(indio_dev,
>> +						     ADXRS290_READ_REG(chan->address),
>> +						     &t);
>> +			if (ret < 0)
>> +				return ret;
>> +			*val = t;
> 
> As mentioned above, you should be fine with using a signed value where you have &t.
> As we don't use *val in the error case, it's fine to write directly into it and
> avoid the need for the local variable t at all.

Okay, will take care of this in v4.

> 
>> +			return IIO_VAL_INT;
>> +		case IIO_TEMP:
>> +			ret = adxrs290_get_temp_data(indio_dev, &t);
>> +			if (ret < 0)
>> +				return ret;
>> +			*val = t;
>> +			return IIO_VAL_INT;
>> +		default:
>> +			return -EINVAL;
>> +		}
>> +	case IIO_CHAN_INFO_SCALE:
>> +		switch (chan->type) {
>> +		case IIO_ANGL_VEL:
>> +			/* 1 LSB = 0.005 degrees/sec */
>> +			*val = 0;
>> +			*val2 = 87266;
>> +			return IIO_VAL_INT_PLUS_NANO;
>> +		case IIO_TEMP:
>> +			/* 1 LSB = 0.1 degrees Celsius */
>> +			*val = 100;
>> +			return IIO_VAL_INT;
>> +		default:
>> +			return -EINVAL;
>> +		}
>> +	case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY:
>> +		switch (chan->type) {
>> +		case IIO_ANGL_VEL:
>> +			t = st->lpf_3db_freq_idx;
>> +			*val = adxrs290_lpf_3db_freq_hz_table[t][0];
>> +			*val2 = adxrs290_lpf_3db_freq_hz_table[t][1];
>> +			return IIO_VAL_INT_PLUS_MICRO;
>> +		default:
>> +			return -EINVAL;
>> +		}
>> +	case IIO_CHAN_INFO_HIGH_PASS_FILTER_3DB_FREQUENCY:
>> +		switch (chan->type) {
>> +		case IIO_ANGL_VEL:
>> +			t = st->hpf_3db_freq_idx;
>> +			*val = adxrs290_hpf_3db_freq_hz_table[t][0];
>> +			*val2 = adxrs290_hpf_3db_freq_hz_table[t][1];
>> +			return IIO_VAL_INT_PLUS_MICRO;
>> +		default:
>> +			return -EINVAL;
>> +		}
>> +	}
>> +
>> +	return -EINVAL;
>> +}
>> +
>> +static int adxrs290_write_raw(struct iio_dev *indio_dev,
>> +			      struct iio_chan_spec const *chan,
>> +			      int val,
>> +			      int val2,
>> +			      long mask)
>> +{
>> +	struct adxrs290_state *st = iio_priv(indio_dev);
>> +	int lpf_idx, hpf_idx;
>> +
>> +	switch (mask) {
>> +	case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY:
>> +		lpf_idx = adxrs290_find_match(adxrs290_lpf_3db_freq_hz_table,
>> +					      ARRAY_SIZE(adxrs290_lpf_3db_freq_hz_table),
>> +					      val, val2);
>> +		if (lpf_idx < 0)
>> +			return -EINVAL;
>> +		/* caching the updated state of the low-pass filter */
>> +		st->lpf_3db_freq_idx = lpf_idx;
>> +		/* retrieving the current state of the high-pass filter */
>> +		hpf_idx = st->hpf_3db_freq_idx;
>> +		return adxrs290_set_filter_freq(indio_dev, lpf_idx, hpf_idx);
>> +	case IIO_CHAN_INFO_HIGH_PASS_FILTER_3DB_FREQUENCY:
>> +		hpf_idx = adxrs290_find_match(adxrs290_hpf_3db_freq_hz_table,
>> +					      ARRAY_SIZE(adxrs290_hpf_3db_freq_hz_table),
>> +					      val, val2);
>> +		if (hpf_idx < 0)
>> +			return -EINVAL;
>> +		/* caching the updated state of the high-pass filter */
>> +		st->hpf_3db_freq_idx = hpf_idx;
>> +		/* retrieving the current state of the low-pass filter */
>> +		lpf_idx = st->lpf_3db_freq_idx;
>> +		return adxrs290_set_filter_freq(indio_dev, lpf_idx, hpf_idx);
>> +	}
>> +
>> +	return -EINVAL;
>> +}
>> +
>> +static int adxrs290_read_avail(struct iio_dev *indio_dev,
>> +			       struct iio_chan_spec const *chan,
>> +			       const int **vals, int *type, int *length,
>> +			       long mask)
>> +{
>> +	switch (mask) {
>> +	case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY:
>> +		*vals = (const int *)adxrs290_lpf_3db_freq_hz_table;
>> +		*type = IIO_VAL_INT_PLUS_MICRO;
>> +		/* Values are stored in a 2D matrix */
>> +		*length = ARRAY_SIZE(adxrs290_lpf_3db_freq_hz_table) * 2;
>> +
>> +		return IIO_AVAIL_LIST;
>> +	case IIO_CHAN_INFO_HIGH_PASS_FILTER_3DB_FREQUENCY:
>> +		*vals = (const int *)adxrs290_hpf_3db_freq_hz_table;
>> +		*type = IIO_VAL_INT_PLUS_MICRO;
>> +		/* Values are stored in a 2D matrix */
>> +		*length = ARRAY_SIZE(adxrs290_hpf_3db_freq_hz_table) * 2;
>> +
>> +		return IIO_AVAIL_LIST;
>> +	default:
>> +		return -EINVAL;
>> +	}
>> +}
>> +
>> +#define ADXRS290_ANGL_VEL_CHANNEL(reg, axis) {				\
>> +	.type = IIO_ANGL_VEL,						\
>> +	.address = reg,							\
>> +	.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_LOW_PASS_FILTER_3DB_FREQUENCY) |		\
>> +	BIT(IIO_CHAN_INFO_HIGH_PASS_FILTER_3DB_FREQUENCY),		\
>> +	.info_mask_shared_by_type_available =				\
>> +	BIT(IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY) |		\
>> +	BIT(IIO_CHAN_INFO_HIGH_PASS_FILTER_3DB_FREQUENCY),		\
>> +}
>> +
>> +static const struct iio_chan_spec adxrs290_channels[] = {
>> +	ADXRS290_ANGL_VEL_CHANNEL(ADXRS290_REG_DATAX0, X),
>> +	ADXRS290_ANGL_VEL_CHANNEL(ADXRS290_REG_DATAY0, Y),
>> +	{
>> +		.type = IIO_TEMP,
>> +		.address = ADXRS290_REG_TEMP0,
>> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
>> +		BIT(IIO_CHAN_INFO_SCALE),
>> +	},
>> +};
>> +
>> +static const struct iio_info adxrs290_info = {
>> +	.read_raw = &adxrs290_read_raw,
>> +	.write_raw = &adxrs290_write_raw,
>> +	.read_avail = &adxrs290_read_avail,
>> +};
>> +
>> +static int adxrs290_probe(struct spi_device *spi)
>> +{
>> +	struct iio_dev *indio_dev;
>> +	struct adxrs290_state *st;
>> +	u8 val, val2;
>> +	int ret;
>> +
>> +	indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));
>> +	if (!indio_dev)
>> +		return -ENOMEM;
>> +
>> +	st = iio_priv(indio_dev);
>> +	st->spi = spi;
>> +	spi_set_drvdata(spi, indio_dev);
> 
> As things currently stand I don't think you ever use this.
> So drop it for now and reintroduce it when you need it (probably when
> you add power management support).

Okay, makes sense. Will remove it in v4.

With regards,
Nishant Malpani

> 
>> +
>> +	indio_dev->name = "adxrs290";
>> +	indio_dev->modes = INDIO_DIRECT_MODE;
>> +	indio_dev->channels = adxrs290_channels;
>> +	indio_dev->num_channels = ARRAY_SIZE(adxrs290_channels);
>> +	indio_dev->info = &adxrs290_info;
>> +
>> +	val = spi_w8r8(spi, ADXRS290_READ_REG(ADXRS290_REG_ADI_ID));
>> +	if (val != ADXRS290_ADI_ID) {
>> +		dev_err(&spi->dev, "Wrong ADI ID 0x%02x\n", val);
>> +		return -ENODEV;
>> +	}
>> +
>> +	val = spi_w8r8(spi, ADXRS290_READ_REG(ADXRS290_REG_MEMS_ID));
>> +	if (val != ADXRS290_MEMS_ID) {
>> +		dev_err(&spi->dev, "Wrong MEMS ID 0x%02x\n", val);
>> +		return -ENODEV;
>> +	}
>> +
>> +	val = spi_w8r8(spi, ADXRS290_READ_REG(ADXRS290_REG_DEV_ID));
>> +	if (val != ADXRS290_DEV_ID) {
>> +		dev_err(&spi->dev, "Wrong DEV ID 0x%02x\n", val);
>> +		return -ENODEV;
>> +	}
>> +
>> +	/* default mode the gyroscope starts in */
>> +	st->mode = STANDBY;
>> +
>> +	/* switch to measurement mode and switch on the temperature sensor */
>> +	ret = adxrs290_initial_setup(indio_dev);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	/* max transition time to measurement mode */
>> +	msleep(ADXRS290_MAX_TRANSITION_TIME_MS);
>> +
>> +	ret = adxrs290_get_3db_freq(indio_dev, &val, &val2);
>> +	if (ret < 0)
>> +		return ret;
>> +
>> +	st->lpf_3db_freq_idx = val;
>> +	st->hpf_3db_freq_idx = val2;
>> +
>> +	return devm_iio_device_register(&spi->dev, indio_dev);
>> +}
>> +
>> +static const struct of_device_id adxrs290_of_match[] = {
>> +	{ .compatible = "adi,adxrs290" },
>> +	{ }
>> +};
>> +MODULE_DEVICE_TABLE(of, adxrs290_of_match);
>> +
>> +static struct spi_driver adxrs290_driver = {
>> +	.driver = {
>> +		.name = "adxrs290",
>> +		.of_match_table = adxrs290_of_match,
>> +	},
>> +	.probe = adxrs290_probe,
>> +};
>> +module_spi_driver(adxrs290_driver);
>> +
>> +MODULE_AUTHOR("Nishant Malpani <nish.malpani25@gmail.com>");
>> +MODULE_DESCRIPTION("Analog Devices ADXRS290 Gyroscope SPI driver");
>> +MODULE_LICENSE("GPL");
>