Re: [PATCH v4 2/3] iio: pressure: Honeywell mprls0025pa pressure sensor

Jonathan Cameron
2023-05-06T15:48:33Z

On Fri, 5 May 2023 15:22:07 +0200
Andreas Klinger <ak@it-klinger.de> wrote:

> Honeywell mprls0025pa is a series of pressure sensors.
>
> Add initial I2C support.
>
> Note:
> - IIO buffered mode is supported
> - SPI mode is not supported
>
> Signed-off-by: Andreas Klinger <ak@it-klinger.de>

Hi Andreas,

A few maths related questions inline + a few other bits noticed
on a fresh read through.

Thanks,

Jonathan

> ---
> drivers/iio/pressure/Kconfig | 13 +
> drivers/iio/pressure/Makefile | 1 +
> drivers/iio/pressure/mprls0025pa.c | 441 +++++++++++++++++++++++++++++
> 3 files changed, 455 insertions(+)
> create mode 100644 drivers/iio/pressure/mprls0025pa.c
>
> diff --git a/drivers/iio/pressure/Kconfig b/drivers/iio/pressure/Kconfig
> index c9453389e4f7..43aef35ce778 100644
> --- a/drivers/iio/pressure/Kconfig
> +++ b/drivers/iio/pressure/Kconfig
> @@ -148,6 +148,19 @@ config MPL3115
> To compile this driver as a module, choose M here: the module
> will be called mpl3115.
>
> +config MPRLS0025PA
> + tristate "Honeywell MPRLS0025PA (MicroPressure sensors series)"
> + depends on I2C
> + select IIO_BUFFER
> + select IIO_TRIGGERED_BUFFER
> + help
> + Say Y here to build support for the Honeywell MicroPressure pressure
> + sensor series. There are many different types with different pressure
> + range. These ranges can be set up in the device tree.
> +
> + To compile this driver as a module, choose M here: the module will be
> + called mprls0025pa.
> +
> config MS5611
> tristate "Measurement Specialties MS5611 pressure sensor driver"
> select IIO_BUFFER
> diff --git a/drivers/iio/pressure/Makefile b/drivers/iio/pressure/Makefile
> index 083ae87ff48f..c90f77210e94 100644
> --- a/drivers/iio/pressure/Makefile
> +++ b/drivers/iio/pressure/Makefile
> @@ -19,6 +19,7 @@ obj-$(CONFIG_MPL115) += mpl115.o
> obj-$(CONFIG_MPL115_I2C) += mpl115_i2c.o
> obj-$(CONFIG_MPL115_SPI) += mpl115_spi.o
> obj-$(CONFIG_MPL3115) += mpl3115.o
> +obj-$(CONFIG_MPRLS0025PA) += mprls0025pa.o
> obj-$(CONFIG_MS5611) += ms5611_core.o
> obj-$(CONFIG_MS5611_I2C) += ms5611_i2c.o
> obj-$(CONFIG_MS5611_SPI) += ms5611_spi.o
> diff --git a/drivers/iio/pressure/mprls0025pa.c b/drivers/iio/pressure/mprls0025pa.c
> new file mode 100644
> index 000000000000..7a8736de6e87
> --- /dev/null
> +++ b/drivers/iio/pressure/mprls0025pa.c
> @@ -0,0 +1,441 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * MPRLS0025PA - Honeywell MicroPressure pressure sensor series driver
> + *
> + * Copyright (c) Andreas Klinger <ak@it-klinger.de>
> + *
> + * Data sheet:
> + * https://prod-edam.honeywell.com/content/dam/honeywell-edam/sps/siot/en-us/
> + * products/sensors/pressure-sensors/board-mount-pressure-sensors/
> + * micropressure-mpr-series/documents/
> + * sps-siot-mpr-series-datasheet-32332628-ciid-172626.pdf
> + *
> + * 7-bit I2C default slave address: 0x18
> + */
> +
> +#include <asm/unaligned.h>
Common convention is put the asm stuff after the linux includes as it's
more specific.

Often you get:

General includes

Subsystem specific includes

asm includes

> +#include <linux/delay.h>
> +#include <linux/device.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/i2c.h>
> +#include <linux/iio/buffer.h>
> +#include <linux/iio/iio.h>
> +#include <linux/iio/trigger_consumer.h>
> +#include <linux/iio/triggered_buffer.h>
> +#include <linux/math64.h>
> +#include <linux/mod_devicetable.h>
> +#include <linux/module.h>
> +#include <linux/property.h>
> +#include <linux/regulator/consumer.h>
> +
> +/* bits in i2c status byte */
> +#define MPR_I2C_POWER BIT(6) /* device is powered */
> +#define MPR_I2C_BUSY BIT(5) /* device is busy */
> +#define MPR_I2C_MEMORY BIT(2) /* integrity test passed */
> +#define MPR_I2C_MATH BIT(0) /* internal math saturation */
> +
> +#define MPR_NANO_PART 1000000000LL

NANO from units.h instead of this?

> +
> +/*
> + * _INPUT interface:

Why _INPUT? I kind of get what you mean, but I'd just call it sysfs
interface and talk about the units the value ends up in rather than
referring to a different sysfs interface the driver correctly isn't
supplying to userspace.

> + * Calculation formular from the datasheet:
> + * pressure = (press_cnt - outputmin) * scale + pmin
> + * with:
> + * * pressure - measured pressure in Pascal
> + * * press_cnt - raw value read from sensor
> + * * pmin - minimum pressure range value of sensor (data->pmin)
> + * * pmax - maximum pressure range value of sensor (data->pmax)
> + * * outputmin - minimum numerical range raw value delivered by sensor
> + * (MPR_OUT_MIN)
> + * * outputmax - maximum numerical range raw value delivered by sensor
> + * (MPR_OUT_MAX)
> + * * scale - (pmax - pmin) / (outputmax - outputmin)
> + *
> + * _RAW interface:
> + * pressure = (raw + offset) * scale
> + * --> need to adjust offset for fitting into _RAW interface
> + * Values for _RAW interface:
> + * * raw - press_cnt
> + * * scale - (pmax - pmin) / (outputmax - outputmin)
> + * * offset - (-1 * outputmin) - pmin / scale
> + * note: With all sensors from the datasheet pmin = 0
> + * which reduces the offset to (-1 * outputmin)
> + */
> +
> +/*
> + * transfer function A: 10% to 90% of 2^24
> + * transfer function B: 2.5% to 22.5% of 2^24
> + * transfer function C: 20% to 80% of 2^24
> + */
> +enum mpr_func_id {
> + MPR_FUNCTION_A,
> + MPR_FUNCTION_B,
> + MPR_FUNCTION_C,
> +};
> +
> +struct mpr_func_spec {
> + u32 output_min;
> + u32 output_max;
> +};
> +
> +static const struct mpr_func_spec mpr_func_spec[] = {
> + [MPR_FUNCTION_A] = {.output_min = 1677722, .output_max = 15099494},
> + [MPR_FUNCTION_B] = {.output_min = 419430, .output_max = 3774874},
> + [MPR_FUNCTION_C] = {.output_min = 3355443, .output_max = 13421773},
> +};
> +
> +struct mpr_chan {
> + s32 pres; /* pressure value */
> + s64 ts; /* timestamp */
> +};
> +
> +struct mpr_data {
> + struct i2c_client *client;
> + struct mutex lock; /* i2c transactions */

That's a little vague. Key bit here I think is to lock the access to the device when
waiting for an interrupt or timeout on a reading, not the transactions themselves.

> + u32 pmin; /* minimal pressure in pascal */
> + u32 pmax; /* maximal pressure in pascal */
> + u32 function; /* transfer function */

Why not enum mpr_func_id ?

> + u32 outmin; /*
> + * minimal numerical range raw
> + * value from sensor
> + */
> + u32 outmax; /*
> + * maximal numerical range raw
> + * value from sensor
> + */
> + int scale; /* int part of scale */
> + int scale2; /* nano part of scale */
> + int offset; /* int part of offset */
> + int offset2; /* nano part of offset */
> + struct gpio_desc *gpiod_reset; /* reset */
> + int irq; /* end of conversion irq */

Only needed in probe, no need for a copy in here.

> + struct completion completion; /* handshake from irq to read */
> + struct mpr_chan chan; /*
> + * channel values for buffered
> + * mode
> + */
> +};

> +/**
> + * mpr_read_pressure() - Read pressure value from sensor via I2C
> + * @data: Pointer to private data struct.
> + * @press: Output value read from sensor.
> + *
> + * Reading from the sensor by sending and receiving I2C telegrams.
> + *
> + * If there is an end of conversion (EOC) interrupt registered the function
> + * waits for a maximum of one second for the interrupt.
> + *
> + * Context: The function can sleep and data->lock should be held when calling it
> + * Return:
> + * * 0 - OK, the pressure value could be read
> + * * -ETIMEDOUT - Timeout while waiting for the EOC interrupt or busy flag is
> + * still set after nloops attempts of reading
> + */
> +static int mpr_read_pressure(struct mpr_data *data, s32 *press)
> +{
> + struct device *dev = &data->client->dev;
> + int ret, i;
> + u8 wdata[] = {0xAA, 0x00, 0x00};
> + s32 status;
> + int nloops = 10;
> + u8 buf[5];
> +
> + reinit_completion(&data->completion);
> +
> + ret = i2c_master_send(data->client, wdata, sizeof(wdata));
> + if (ret < 0) {
> + dev_err(dev, "error while writing ret: %d\n", ret);
> + return ret;
> + }
> + if (ret != sizeof(wdata)) {
> + dev_err(dev, "received size doesn't fit - ret: %d / %u\n", ret,
> + sizeof(wdata));
> + return -EIO;
> + }
> +
> + if (data->irq > 0) {
> + ret = wait_for_completion_timeout(&data->completion, HZ);
> + if (!ret) {
> + dev_err(dev, "timeout while waiting for eoc irq\n");
> + return -ETIMEDOUT;
> + }
> + } else {
> + /* wait until status indicates data is ready */
> + for (i = 0; i < nloops; i++) {
> + /*
> + * datasheet only says to wait at least 5 ms for the
> + * data but leave the maximum response time open
> + * --> let's try it nloops (10) times which seems to be
> + * quite long
> + */
> + usleep_range(5000, 10000);
> + status = i2c_smbus_read_byte(data->client);
> + if (status < 0) {
> + dev_err(dev,
> + "error while reading, status: %d\n",
> + status);
> + return status;
> + }
> + if (!(status & MPR_I2C_BUSY))
> + break;
> + }
> + if (i == nloops) {
> + dev_err(dev, "timeout while reading\n");
> + return -ETIMEDOUT;
> + }
> + }
> +
> + ret = i2c_master_recv(data->client, buf, sizeof(buf));
> + if (ret < 0) {
> + dev_err(dev, "error in i2c_master_recv ret: %d\n", ret);
> + return ret;
> + }
> + if (ret != sizeof(buf)) {
> + dev_err(dev, "received size doesn't fit - ret: %d / %u\n", ret,
> + sizeof(buf));
> + return -EIO;
> + }
> +
> + if (buf[0] & MPR_I2C_BUSY) {
> + /*
> + * it should never be the case that status still indicates
> + * business
> + */
> + dev_err(dev, "data still not ready: %08x\n", buf[0]);
> + return -ETIMEDOUT;
> + }
> +
> + *press = get_unaligned_be24(&buf[1]);

Is it necessary to read the 5th byte even though it's never touched?
A quick galnce at datasheet shows no mention of that byte so I'm a little confused.

> +
> + dev_dbg(dev, "received: %*ph cnt: %d\n", ret, buf, *press);
> +
> + return 0;
> +}
> +
> +static irqreturn_t mpr_eoc_handler(int irq, void *p)
> +{
> + struct mpr_data *data = (struct mpr_data *)p;

You should never need to cast explicitly from a void * (C spec thing)
Hence I don't think that cast is necessary.

> +
> + complete(&data->completion);
> +
> + return IRQ_HANDLED;
> +}
> +
> +static irqreturn_t mpr_trigger_handler(int irq, void *p)
> +{
> + int ret;
> + struct iio_poll_func *pf = p;
> + struct iio_dev *indio_dev = pf->indio_dev;
> + struct mpr_data *data = iio_priv(indio_dev);
> +
> + mutex_lock(&data->lock);
> + ret = mpr_read_pressure(data, &data->chan.pres);
> + if (ret < 0) {
> + mutex_unlock(&data->lock);

Move the err label above the mutex unlock then go to that instead, allowing
you to unlock in just one place.

> + goto err;
> + }
> +
> + iio_push_to_buffers_with_timestamp(indio_dev, &data->chan,
> + iio_get_time_ns(indio_dev));
> + mutex_unlock(&data->lock);
> +
> +err:
> + iio_trigger_notify_done(indio_dev->trig);
> +
> + return IRQ_HANDLED;
> +}
> +

> +static int mpr_probe(struct i2c_client *client)
> +{

> + data->outmin = mpr_func_spec[data->function].output_min;
> + data->outmax = mpr_func_spec[data->function].output_max;
> +
> + scale = div_s64(((s64)(data->pmax - data->pmin)) * MPR_NANO_PART,

NANO.

> + data->outmax - data->outmin);
> + data->scale = div_s64(scale, MPR_NANO_PART);
> + data->scale2 = scale - data->scale * MPR_NANO_PART;

As below, I'm not seeing why div_s64_rem() isn't appropriate for this
as well as making it immediately obvious what is going on.

> +
> + offset = ((-1LL) * (s64)data->outmin) * MPR_NANO_PART -

> + div_s64(div_s64((s64)data->pmin * MPR_NANO_PART, scale),
> + MPR_NANO_PART);

I'm guessing the multiply by MPR_NANO_PART then divide by it is to maintain precision?
If so I'd like a comment here explaining the logic behind it.

> + data->offset = div_s64(offset, MPR_NANO_PART);
> + data->offset2 = offset - data->offset * MPR_NANO_PART;

Is this a round about way of doing offset % NANO?
div_s64_rem() appropriate here?

> +
> + if (data->irq > 0) {
> + ret = devm_request_irq(dev, data->irq, mpr_eoc_handler,
> + IRQF_TRIGGER_RISING, client->name, data);
> + if (ret)
> + return dev_err_probe(dev, ret,
> + "request irq %d failed\n", data->irq);
> + }
> +
> + data->gpiod_reset = devm_gpiod_get_optional(dev, "reset",
> + GPIOD_OUT_HIGH);
> + if (IS_ERR(data->gpiod_reset))
> + return dev_err_probe(dev, PTR_ERR(data->gpiod_reset),
> + "request reset-gpio failed\n");
> +
> + mpr_reset(data);
> +
> + ret = devm_iio_triggered_buffer_setup(dev, indio_dev, NULL,
> + mpr_trigger_handler, NULL);
> + if (ret)
> + return dev_err_probe(dev, ret,
> + "iio triggered buffer setup failed\n");
> +
> + ret = devm_iio_device_register(dev, indio_dev);
> + if (ret)
> + return dev_err_probe(dev, ret,
> + "unable to register iio device\n");
> +
> + return 0;
> +}