Re: [PATCH 2/2] iio: accel: Add driver for Murata SCA3300 accelerometer

Jonathan Cameron
2021-04-12T11:09:52Z

On Mon, 12 Apr 2021 10:50:56 +0300
Tomas Melin <tomas.melin@vaisala.com> wrote:

> Add initial support for Murata SCA3300 3-axis industrial
> accelerometer with digital SPI interface. This device also
> provides a temperature measurement.
>
> Device product page including datasheet can be found at:
> https://www.murata.com/en-global/products/sensor/accel/sca3300
>
> Signed-off-by: Tomas Melin <tomas.melin@vaisala.com>

Hi Tomas,

Comments below.

Thanks,

Jonathan

> ---
> drivers/iio/accel/Kconfig | 13 ++
> drivers/iio/accel/Makefile | 1 +
> drivers/iio/accel/sca3300.c | 434 ++++++++++++++++++++++++++++++++++++
> 3 files changed, 448 insertions(+)
> create mode 100644 drivers/iio/accel/sca3300.c
>
> diff --git a/drivers/iio/accel/Kconfig b/drivers/iio/accel/Kconfig
> index cceda3cecbcf..0dbf7b648e8a 100644
> --- a/drivers/iio/accel/Kconfig
> +++ b/drivers/iio/accel/Kconfig
> @@ -450,6 +450,19 @@ config SCA3000
> To compile this driver as a module, say M here: the module will be
> called sca3000.
>
> +config SCA3300
> + tristate "Murata SCA3300 3-Axis Accelerometer Driver"
> + depends on SPI
> + select CRC8
> + select IIO_BUFFER
> + select IIO_TRIGGERED_BUFFER
> + help
> + Say yes here to build support for Murata SCA3300 3-Axis
> + accelerometer.
> +
> + To compile this driver as a module, choose M here: the module will be
> + called sca3300.
> +
> config STK8312
> tristate "Sensortek STK8312 3-Axis Accelerometer Driver"
> depends on I2C
> diff --git a/drivers/iio/accel/Makefile b/drivers/iio/accel/Makefile
> index 32cd1342a31a..4b56527a2b97 100644
> --- a/drivers/iio/accel/Makefile
> +++ b/drivers/iio/accel/Makefile
> @@ -50,6 +50,7 @@ obj-$(CONFIG_MXC4005) += mxc4005.o
> obj-$(CONFIG_MXC6255) += mxc6255.o
>
> obj-$(CONFIG_SCA3000) += sca3000.o
> +obj-$(CONFIG_SCA3300) += sca3300.o
>
> obj-$(CONFIG_STK8312) += stk8312.o
> obj-$(CONFIG_STK8BA50) += stk8ba50.o
> diff --git a/drivers/iio/accel/sca3300.c b/drivers/iio/accel/sca3300.c
> new file mode 100644
> index 000000000000..112fb88ecd3a
> --- /dev/null
> +++ b/drivers/iio/accel/sca3300.c
> @@ -0,0 +1,434 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) Vaisala Oyj. All rights reserved.

Give a year for the copyright notice if you can.

> + */
> +#include <linux/crc8.h>
> +#include <linux/delay.h>
> +#include <linux/iio/buffer.h>
> +#include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.h>
> +#include <linux/iio/trigger_consumer.h>
> +#include <linux/iio/triggered_buffer.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/spi/spi.h>
> +
> +#define SCA3300_ALIAS "sca3300"
> +
> +#define SCA3300_REG_STATUS 0x6
> +#define SCA3300_REG_MODE 0xd
> +#define SCA3300_REG_WHOAMI 0x10
> +#define SCA3300_VALUE_SW_RESET 0x20
> +#define SCA3300_CRC8_POLYNOMIAL 0x1d
> +#define SCA3300_X_READ 0

I wouldn't bother defining this.

> +#define SCA3300_X_WRITE BIT(7)

Even this one is something I'd just put inline with a comment.

> +#define SCA3300_DEVICE_ID 0x51
> +#define SCA3300_RS_ERROR 0x3
> +
> +enum sca3300_scan_indexes {
> + SCA3300_ACC_X = 0,
> + SCA3300_ACC_Y,
> + SCA3300_ACC_Z,
> + SCA3300_TEMP,
> + SCA3300_TIMESTAMP,
> +};
> +
> +#define SCA3300_ACCEL_CHANNEL(index, reg, axis) { \
> + .type = IIO_ACCEL, \
> + .address = reg, \
> + .modified = 1, \
> + .channel2 = IIO_MOD_##axis, \
> + .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) | \
> + BIT(IIO_CHAN_INFO_PROCESSED), \

As mentioned below, don't provide PROCESSED. Userspace is better at handling the
conversion so leave it to them.

> + .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), \
> + .scan_index = index, \
> + .scan_type = { \
> + .sign = 's', \
> + .realbits = 16, \
> + .storagebits = 16, \
> + .shift = 0, \
> + .endianness = IIO_CPU, \
> + }, \
> + }
> +
> +static const struct iio_chan_spec sca3300_channels[] = {
> + SCA3300_ACCEL_CHANNEL(SCA3300_ACC_X, 0x1, X),
> + SCA3300_ACCEL_CHANNEL(SCA3300_ACC_Y, 0x2, Y),
> + SCA3300_ACCEL_CHANNEL(SCA3300_ACC_Z, 0x3, Z),
> + {
> + .type = IIO_TEMP,
> + .address = 0x5,
> + .scan_index = SCA3300_TEMP,
> + .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> + .scan_type = {
> + .sign = 's',
> + .realbits = 16,
> + .storagebits = 16,
> + .shift = 0,
> + .endianness = IIO_CPU,
> + },
> + },
> + IIO_CHAN_SOFT_TIMESTAMP(4),
> +};
> +
> +static const int sca3300_accel_scale[] = {2700, 1350, 5400, 5400};
> +
> +static const unsigned long sca3300_scan_masks[] = {
> + BIT(SCA3300_ACC_X) | BIT(SCA3300_ACC_Y) | BIT(SCA3300_ACC_Z) |
> + BIT(SCA3300_TEMP),
> + 0};
> +
> +/**
> + * SCA3300 device data

run scripts/kernel-doc over the file and fix the warnings + errors.

> + *
> + * @spi SPI device structure
> + * @opmode Device operation mode
> + * @lock Data buffer lock
> + * @txbuf Transmit buffer
> + * @rxbuf Receive buffer
> + * @scan Triggered buffer. Four channel 16-bit data + 64-bit timestamp
> + */
> +struct sca3300_data {
> + struct spi_device *spi;
> + u32 opmode;
> + struct mutex lock;
> + u8 txbuf[4];
> + u8 rxbuf[4];
> + struct {
> + s16 channels[4];
> + s64 ts __aligned(sizeof(s64));
> + } scan;
> +};
> +
> +DECLARE_CRC8_TABLE(sca3300_crc_table);
> +
> +static int sca3300_transfer(struct sca3300_data *sca_data, int *val)
> +{
> + struct spi_delay delay = {.value = 10, .unit = SPI_DELAY_UNIT_USECS};
> + int32_t ret;
> + int rs;
> + u8 crc;
> + struct spi_transfer xfers[2] = {
> + {
> + .tx_buf = sca_data->txbuf,
> + .rx_buf = NULL,
> + .len = ARRAY_SIZE(sca_data->txbuf),
> + .delay = delay,
> + .cs_change = 1,
> + },
> + {
> + .tx_buf = NULL,
> + .rx_buf = sca_data->rxbuf,
> + .len = ARRAY_SIZE(sca_data->rxbuf),
> + .delay = delay,
> + .cs_change = 0,
> + }
> + };
> +
> + /* inverted crc value as described in device data sheet */
> + crc = ~crc8(sca3300_crc_table, &sca_data->txbuf[0], 3, CRC8_INIT_VALUE);
> + sca_data->txbuf[3] = crc;
> +
> + ret = spi_sync_transfer(sca_data->spi, xfers, 2);

Use ARRAY_SIZE(xfers) instead of 2.

> + if (ret < 0) {
> + dev_err(&sca_data->spi->dev,
> + "transfer error, error: %d\n", ret);
> + return -EIO;
> + }
> +
> + crc = ~crc8(sca3300_crc_table, &sca_data->rxbuf[0], 3, CRC8_INIT_VALUE);
> + if (sca_data->rxbuf[3] != crc) {
> + dev_err(&sca_data->spi->dev, "CRC checksum mismatch");
> + return -EIO;
> + }
> +
> + /* get return status */
> + rs = sca_data->rxbuf[0] & 0x03;
> + if (rs == SCA3300_RS_ERROR)
> + return rs;
> +
> + *val = (s16)(sca_data->rxbuf[2] | (sca_data->rxbuf[1] << 8));

Preference for an unaligned endian conversion here and explicit sign extend e.g
something like

sign_extend32(get_unaligned_le16(&sca_data->rxbuf[1]), 15)

> +
> + return 0;
> +}
> +
> +static int sca3300_read_reg(struct sca3300_data *sca_data, u8 reg, int *val)
> +{
> + int ret;
> +
> + mutex_lock(&sca_data->lock);
> + sca_data->txbuf[0] = SCA3300_X_READ | (reg << 2);
> + ret = sca3300_transfer(sca_data, val);
> + if (ret > 0) {
> + sca_data->txbuf[0] = SCA3300_X_READ | (SCA3300_REG_STATUS << 2);
> + ret = sca3300_transfer(sca_data, val);
> + /* status 0 = startup, 0x2 = mode change */
> + if (ret > 0 && *val != 0 && *val != 0x2) {
> + dev_err_ratelimited(&sca_data->spi->dev,
> + "device status: %x\n",
> + (u16)*val);
> + mutex_unlock(&sca_data->lock);
> + return -EIO;
> + }
> + if (ret > 0)
> + ret = 0;
> + }
> + mutex_unlock(&sca_data->lock);
> +
> + return ret;
> +}
> +
> +static int sca3300_write_reg(struct sca3300_data *sca_data, u8 reg, int val)
> +{
> + int reg_val = 0;
> + int ret;
> +
> + mutex_lock(&sca_data->lock);
> + sca_data->txbuf[0] = SCA3300_X_WRITE | (reg << 2);
> + sca_data->txbuf[1] = val >> 8;
> + sca_data->txbuf[2] = val & 0xFF;

Prefer (Slightly) an unaligned put.

> + ret = sca3300_transfer(sca_data, &reg_val);
> + if (ret > 0) {

Factor this error handling out to another function, plus trigger it from an
appropriate standard error code rather than a positive return value.

> + sca_data->txbuf[0] = SCA3300_X_READ | (SCA3300_REG_STATUS << 2);
> + ret = sca3300_transfer(sca_data, &reg_val);
> + /* status 0 = startup, 0x2 = mode change */
> + if (ret > 0 && reg_val != 0 && reg_val != 0x2) {
> + dev_err_ratelimited(&sca_data->spi->dev,
> + "device status: %x\n",
> + (u16)reg_val);
> + mutex_unlock(&sca_data->lock);
> + return -EIO;
> + }
> + if (ret > 0)
> + ret = 0;

Whenever you get this sort of juggling it rather implies your design is
less than ideal.

> + }
> + mutex_unlock(&sca_data->lock);
> +
> + return ret;
> +}
> +
> +static int sca3300_write_raw(struct iio_dev *indio_dev,
> + struct iio_chan_spec const *chan,
> + int val, int val2, long mask)
> +{
> + struct sca3300_data *data = iio_priv(indio_dev);
> +
> + switch (mask) {
> + case IIO_CHAN_INFO_SCALE:
> + if (val < 0 || val > 3)
> + return -EINVAL;

No. Scale values need to be the value of 1LSB not a random integer
that requires you to look up the datasheet.

> + return sca3300_write_reg(data, SCA3300_REG_MODE, val);
> + default:
> + return -EINVAL;
> + }
> +}
> +
> +static int sca3300_read_raw(struct iio_dev *indio_dev,
> + struct iio_chan_spec const *chan,
> + int *val, int *val2, long mask)
> +{
> + struct sca3300_data *data = iio_priv(indio_dev);
> + int ret;
> + int reg_val;
> +
> + switch (mask) {
> + case IIO_CHAN_INFO_RAW:
> + ret = sca3300_read_reg(data, chan->address, val);
> + if (ret < 0)
> + return ret;
> + return IIO_VAL_INT;
> + case IIO_CHAN_INFO_SCALE:
> + ret = sca3300_read_reg(data, SCA3300_REG_MODE, &reg_val);
> + if (ret < 0)
> + return ret;
> + *val = sca3300_accel_scale[reg_val];

Scale is very very rarely an integer value which makes me wonder what
you are returning here... It should be the multiplier needed to
take the raw value to a reading in m/sec^2 Given you use it as fractional
below, I'm guessing this is 1/scale_value?

> + return IIO_VAL_INT;
> + case IIO_CHAN_INFO_PROCESSED:
Don't provide processed here. Userspace needs to do the conversion itself
(and given it has floating point easily available will probably do a better
job than we can). I'm assuming the mode can't autonomously change?

> + ret = sca3300_read_reg(data, SCA3300_REG_MODE, &reg_val);
> + if (ret < 0)
> + return ret;
> + *val2 = sca3300_accel_scale[reg_val];
> + ret = sca3300_read_reg(data, chan->address, val);
> + if (ret < 0)
> + return ret;
> + return IIO_VAL_FRACTIONAL;
> + default:
> + return -EINVAL;
> + }
> +}
> +
> +static irqreturn_t sca3300_trigger_handler(int irq, void *p)
> +{
> + struct iio_poll_func *pf = p;
> + struct iio_dev *indio_dev = pf->indio_dev;
> + struct sca3300_data *data = iio_priv(indio_dev);
> + s64 time_ns = iio_get_time_ns(indio_dev);

Is the timestamp at the start more accurate that that at the end
of reading the channels? If not, just put this inline in the
iio_push_to_buffers_with_timestamp() call.

> + int bit, ret, val, i = 0;
> +
> + for_each_set_bit(bit, indio_dev->active_scan_mask,
> + indio_dev->masklength) {
> + ret = sca3300_read_reg(data, sca3300_channels[bit].address,
> + &val);
> + if (ret < 0)

Given we can't return an error code from interrupt handlers, it is usually
a good idea to print something to the log. Otherwise we get missing data
with no idea of why..

> + goto out;
> + if (ARRAY_SIZE(data->scan.channels) > i)

How could this not be true? If it's always true, don't bother
checking i.

> + ((s16 *)data->scan.channels)[i++] = val;
> + }
> +
> + iio_push_to_buffers_with_timestamp(indio_dev, &data->scan, time_ns);
> +out:
> + iio_trigger_notify_done(indio_dev->trig);
> +
> + return IRQ_HANDLED;
> +}
> +
> +static int sca3300_init(struct sca3300_data *sca_data,
> + struct iio_dev *indio_dev)
> +{
> + int ret;
> + int value = 0;
> +
> + if (sca_data->opmode < 1 || sca_data->opmode > 4)
> + return -EINVAL;

Whilst this is going anyway, better to check that next to where
it is read so we drop out immediately rather than buried in this
function.

> +
> + ret = sca3300_write_reg(sca_data, SCA3300_REG_MODE,
> + SCA3300_VALUE_SW_RESET);
> + if (ret != 0)
> + return ret;

For sleeps, good to reference which section in data sheet gives the
timing.

> + usleep_range(2e3, 10e3);
> +
> + ret = sca3300_write_reg(sca_data, SCA3300_REG_MODE,
> + sca_data->opmode - 1);
> + if (ret != 0)
if (ret) see below.

> + return ret;
> + msleep(100);

Again, document where the time comes from. Saves reviewers time if
they want to check it. (I'm too lazy :)

> + ret = sca3300_read_reg(sca_data, SCA3300_REG_WHOAMI, &value);
> + if (ret != 0)

if (ret) is more idiomatic in kernel code.

> + return ret;
> +
> + if (value != SCA3300_DEVICE_ID) {
> + dev_err(&sca_data->spi->dev, "device id not expected value\n");

Perhaps useful to print what was expected and what was seen. Maybe it's
a new variant and this might help the user to identify that and add it to the
driver.

> + return -EIO;

-EINVAL probably more appropriate return.

> + }
> + return 0;
> +}
> +
> +static int sca3300_debugfs_reg_access(struct iio_dev *indio_dev,
> + unsigned int reg, unsigned int writeval,
> + unsigned int *readval)
> +{
> + struct sca3300_data *data = iio_priv(indio_dev);
> + int value;
> + int ret;
> +
> + if (reg > 0x1f)

Use a define that names that register.

> + return -EINVAL;
> +
> + if (!readval)
> + return sca3300_write_reg(data, reg, writeval);
> +
> + ret = sca3300_read_reg(data, reg, &value);
> + if (ret < 0)
> + return ret;
> +
> + *readval = (unsigned int)value;
> +
> + return 0;
> +}
> +
> +static const struct iio_info sca3300_info = {
> + .read_raw = sca3300_read_raw,
> + .write_raw = sca3300_write_raw,
> + .debugfs_reg_access = &sca3300_debugfs_reg_access,
> +};
> +
> +static int sca3300_probe(struct spi_device *spi)
> +{
> + struct sca3300_data *sca_data;
> + struct iio_dev *indio_dev;
> + int ret;
> +
> + indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*sca_data));
> + if (!indio_dev) {
> + dev_err(&spi->dev,
> + "failed to allocate memory for iio device\n");
> + return -ENOMEM;
> + }
> +
> + sca_data = iio_priv(indio_dev);
> + mutex_init(&sca_data->lock);
> + sca_data->spi = spi;
> + spi_set_drvdata(spi, indio_dev);

Won't be used once using devm as below and remove() is dropped, so drop this.

> +
> + crc8_populate_msb(sca3300_crc_table, SCA3300_CRC8_POLYNOMIAL);
> +
> + indio_dev->dev.parent = &spi->dev;
> + indio_dev->info = &sca3300_info;
> + indio_dev->name = SCA3300_ALIAS;
> + indio_dev->modes = INDIO_DIRECT_MODE | INDIO_BUFFER_TRIGGERED;

BUFFER_TRIGGERED bit now set by iio_triggered_buffer_setup() so shouldn't
be ehre as well.

> + indio_dev->channels = sca3300_channels;
> + indio_dev->num_channels = ARRAY_SIZE(sca3300_channels);
> + indio_dev->available_scan_masks = sca3300_scan_masks;
> +
> + if (spi->dev.of_node) {
> + ret = of_property_read_u32(spi->dev.of_node, "murata,opmode",

Please use generic firmware access calls rather than the of specific ones.
That lets us get ACPI support for free :)

As per the binding review however, this one needs to go in favour of userspace
control of scale + filter frequencies / sampling freq.

> + &sca_data->opmode);
> + if (ret < 0)
> + return ret;
> + }
> +
> + ret = sca3300_init(sca_data, indio_dev);
> + if (ret < 0) {
> + dev_err(&spi->dev, "failed to init device, error: %d\n", ret);
> + return ret;
> + }
> +
> + ret = iio_triggered_buffer_setup(indio_dev, iio_pollfunc_store_time,
> + sca3300_trigger_handler, NULL);

devm_iio_triggered_buffer_setup() and you can drop the manual cleanup in remove()
and hence drop remove() entirely as nothing else left.

> + if (ret < 0) {
> + dev_err(&spi->dev,
> + "iio triggered buffer setup failed, error: %d\n", ret);
> + return ret;
> + }
> +
> + ret = devm_iio_device_register(&spi->dev, indio_dev);
> + if (ret < 0) {
> + dev_err(&spi->dev, "iio device register failed, error: %d\n",
> + ret);
> + iio_triggered_buffer_cleanup(indio_dev);
With devm above, no need to manually clean this up.

> + return ret;
> + }
> +
> + return 0;
> +}
> +
> +static int sca3300_remove(struct spi_device *spi)
> +{
> + struct iio_dev *indio_dev = spi_get_drvdata(spi);
> +
> + iio_triggered_buffer_cleanup(indio_dev);
> + return 0;
> +}
> +
> +static const struct of_device_id sca3300_dt_ids[] = {
> + { .compatible = "murata,sca3300"},
> + {},
> +};
> +MODULE_DEVICE_TABLE(of, sca3300_dt_ids);
> +
> +static struct spi_driver sca3300_driver = {
> + .driver = {
> + .name = SCA3300_ALIAS,
> + .owner = THIS_MODULE,
> + .of_match_table = of_match_ptr(sca3300_dt_ids),
> + },
> +
> + .probe = sca3300_probe,
> + .remove = sca3300_remove,
> +};
> +
> +module_spi_driver(sca3300_driver);
> +
> +MODULE_AUTHOR("Tomas Melin <tomas.melin@vaisala.com>");
> +MODULE_DESCRIPTION("Murata SCA3300 SPI Accelerometer");
> +MODULE_LICENSE("GPL v2");