Date:   Mon, 26 Apr 2021 12:25:36 +0200
From:   Tomasz Duszynski <tomasz.duszynski@...akon.com>
To:     Jonathan Cameron <jic23@...nel.org>
CC:     Tomasz Duszynski <tomasz.duszynski@...akon.com>,
        <linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <lars@...afoo.de>,
        <robh+dt@...nel.org>
Subject: Re: [PATCH 2/3] iio: sps30: add support for serial interface

On Sun, Apr 25, 2021 at 04:53:44PM +0100, Jonathan Cameron wrote:
> On Sun, 25 Apr 2021 15:55:45 +0200
> Tomasz Duszynski <tomasz.duszynski@...akon.com> wrote:
>
> > Sensor has support for both i2c and serial communication interfaces.
> > Both offer very similar set of features. Minor differences don't impact
> > overall functionality like doing measurements, etc.
> >
> > Support for i2c have already been added, this patch adds support
> > for the latter ie. serial interface.
> >
> > Signed-off-by: Tomasz Duszynski <tomasz.duszynski@...akon.com>
>
> Hi Tomasz,
>
> A few things inline that need tidying up.
>
> I'm far from an expert on serdev drivers though so I'm not 100% sure on that
> side of things.
>
> Thanks,
>
> Jonathan
>
> > ---
> >  MAINTAINERS                         |   1 +
> >  drivers/iio/chemical/Kconfig        |  10 +
> >  drivers/iio/chemical/Makefile       |   1 +
> >  drivers/iio/chemical/sps30_serial.c | 420 ++++++++++++++++++++++++++++
> >  4 files changed, 432 insertions(+)
> >  create mode 100644 drivers/iio/chemical/sps30_serial.c
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 4b39a9c48736..cab9a63ad2cf 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -16138,6 +16138,7 @@ S:	Maintained
> >  F:	Documentation/devicetree/bindings/iio/chemical/sensirion,sps30.yaml
> >  F:	drivers/iio/chemical/sps30.c
> >  F:	drivers/iio/chemical/sps30_i2c.c
> > +F:	drivers/iio/chemical/sps30_serial.c
> >
> >  SERIAL DEVICE BUS
> >  M:	Rob Herring <robh@...nel.org>
> > diff --git a/drivers/iio/chemical/Kconfig b/drivers/iio/chemical/Kconfig
> > index 82af5f62fbc6..6909b4754b9e 100644
> > --- a/drivers/iio/chemical/Kconfig
> > +++ b/drivers/iio/chemical/Kconfig
> > @@ -153,6 +153,16 @@ config SPS30_I2C
> >  	  To compile this driver as a module, choose M here: the module will
> >  	  be called sps30_i2c.
> >
> > +config SPS30_SERIAL
> > +	tristate "SPS30 particulate matter sensor serial driver"
> > +	depends on SPS30 && SERIAL_DEV_BUS
> > +	help
> > +	  Say Y here to build support for the Sensirion SPS30 serial interface
> > +	  driver.
> > +
> > +	  To compile this driver as a module, choose M here: the module will
> > +	  be called sps30_serial.
> > +
> >  config VZ89X
> >  	tristate "SGX Sensortech MiCS VZ89X VOC sensor"
> >  	depends on I2C
> > diff --git a/drivers/iio/chemical/Makefile b/drivers/iio/chemical/Makefile
> > index 41c264a229c0..4898690cc155 100644
> > --- a/drivers/iio/chemical/Makefile
> > +++ b/drivers/iio/chemical/Makefile
> > @@ -18,4 +18,5 @@ obj-$(CONFIG_SCD30_SERIAL) += scd30_serial.o
> >  obj-$(CONFIG_SENSIRION_SGP30)	+= sgp30.o
> >  obj-$(CONFIG_SPS30) += sps30.o
> >  obj-$(CONFIG_SPS30_I2C) += sps30_i2c.o
> > +obj-$(CONFIG_SPS30_SERIAL) += sps30_serial.o
> >  obj-$(CONFIG_VZ89X)		+= vz89x.o
> > diff --git a/drivers/iio/chemical/sps30_serial.c b/drivers/iio/chemical/sps30_serial.c
> > new file mode 100644
> > index 000000000000..5adeeed9bc8f
> > --- /dev/null
> > +++ b/drivers/iio/chemical/sps30_serial.c
> > @@ -0,0 +1,420 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Sensirion SPS30 particulate matter sensor serial driver
> > + *
> > + * Copyright (c) 2021 Tomasz Duszynski <tomasz.duszynski@...akon.com>
> > + */
> > +#include <linux/completion.h>
> > +#include <linux/device.h>
> > +#include <linux/errno.h>
> > +#include <linux/iio/iio.h>
> > +#include <linux/mod_devicetable.h>
> > +#include <linux/module.h>
> > +#include <linux/serdev.h>
> > +
> > +#include "sps30.h"
> > +
> > +#define SPS30_SERIAL_SOF_EOF 0x7e
> > +#define SPS30_SERIAL_TIMEOUT msecs_to_jiffies(20)
> > +#define SPS30_SERIAL_MAX_BUF_SIZE 263
> > +#define SPS30_SERIAL_ESCAPE_CHAR 0x7d
> > +
> > +#define SPS30_SERIAL_FRAME_MIN_SIZE 7
> > +#define SPS30_SERIAL_FRAME_ADR_OFFSET 1
> > +#define SPS30_SERIAL_FRAME_CMD_OFFSET 2
> > +#define SPS30_SERIAL_FRAME_MOSI_LEN_OFFSET 3
> > +#define SPS30_SERIAL_FRAME_MISO_STATE_OFFSET 3
> > +#define SPS30_SERIAL_FRAME_MISO_LEN_OFFSET 4
> > +#define SPS30_SERIAL_FRAME_MISO_DATA_OFFSET 5
> > +
> > +#define SPS30_SERIAL_START_MEAS 0x00
> > +#define SPS30_SERIAL_STOP_MEAS 0x01
> > +#define SPS30_SERIAL_READ_MEAS 0x03
> > +#define SPS30_SERIAL_RESET 0xd3
> > +#define SPS30_SERIAL_CLEAN_FAN 0x56
> > +#define SPS30_SERIAL_PERIOD 0x80
> > +#define SPS30_SERIAL_DEV_INFO 0xd0
> > +#define SPS30_SERIAL_READ_VERSION 0xd1
> > +
> > +struct sps30_serial_priv {
> > +	struct completion new_frame;
> > +	char buf[SPS30_SERIAL_MAX_BUF_SIZE];
> > +	int num;
> > +	unsigned int chksum;
> > +	bool escaped;
> > +	bool done;
> > +};
> > +
> > +static int sps30_serial_xfer(struct sps30_state *state, const char *buf, int size)
> > +{
> > +	struct serdev_device *serdev = to_serdev_device(state->dev);
> > +	struct sps30_serial_priv *priv = state->priv;
> > +	int ret;
> > +
> > +	priv->num = 0;
> > +	priv->chksum = 0;
> > +	priv->escaped = false;
> > +	priv->done = false;
> > +
> > +	ret = serdev_device_write(serdev, buf, size, SPS30_SERIAL_TIMEOUT);
> > +	if (ret < 0)
> > +		return ret;
> > +	if (ret != size)
> > +		return -EIO;
> > +
> > +	ret = wait_for_completion_interruptible_timeout(&priv->new_frame, SPS30_SERIAL_TIMEOUT);
> > +	if (ret < 0)
> > +		return ret;
> > +	if (!ret)
> > +		return -ETIMEDOUT;
> > +
> > +	return 0;
> > +}
> > +
> > +static struct {
> > +	char byte;
> > +	char byte2;
> > +} sps30_serial_bytes[] = {
> > +	{ 0x11, 0x31 },
> > +	{ 0x13, 0x33 },
> > +	{ 0x7e, 0x5e },
> > +	{ 0x7d, 0x5d },
> > +};
> > +
> > +static int sps30_serial_put_byte(char *buf, char byte)
> > +{
> > +	int i;
> > +
> > +	for (i = 0; i < ARRAY_SIZE(sps30_serial_bytes); i++) {
> > +		if (sps30_serial_bytes[i].byte != byte)
> > +			continue;
> > +
> > +		buf[0] = SPS30_SERIAL_ESCAPE_CHAR;
> > +		buf[1] = sps30_serial_bytes[i].byte2;
> > +
> > +		return 2;
> > +	}
> > +
> > +	buf[0] = byte;
> > +
> > +	return 1;
> > +}
> > +
> > +static char sps30_serial_get_byte(bool escaped, char byte2)
> > +{
> > +	int i;
> > +
> > +	if (!escaped)
> > +		return byte2;
> > +
> > +	for (i = 0; i < ARRAY_SIZE(sps30_serial_bytes); i++) {
> > +		if (sps30_serial_bytes[i].byte2 != byte2)
> > +			continue;
> > +
> > +		return sps30_serial_bytes[i].byte;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int sps30_serial_prep_frame(char *buf, char cmd, const char *arg, int arg_size)
> > +{
> > +	unsigned int chksum;
> > +	unsigned char byte;
> > +	int i, num = 0;
> > +
> > +	buf[num++] = SPS30_SERIAL_SOF_EOF;
> > +	buf[num++] = 0;
> > +
> > +	byte = cmd;
> > +	num += sps30_serial_put_byte(buf + num, byte);
> > +	chksum = byte;
> > +
> > +	byte = (unsigned char)arg_size;
> > +	num += sps30_serial_put_byte(buf + num, byte);
> > +	chksum += byte;
> > +
> > +	for (i = 0; i < arg_size; i++) {
> > +		byte = arg[i];
> > +		num += sps30_serial_put_byte(buf + num, byte);
> > +		chksum += byte;
> > +	}
> > +
> > +	byte = (unsigned char)~chksum;
> > +	num += sps30_serial_put_byte(buf + num, byte);
> > +
> > +	buf[num++] = SPS30_SERIAL_SOF_EOF;
> > +
> > +	return num;
> > +}
> > +
> > +static bool sps30_serial_frame_valid(struct sps30_state *state, const char *buf)
> > +{
> > +	struct sps30_serial_priv *priv = state->priv;
> > +
> > +	if ((priv->num < SPS30_SERIAL_FRAME_MIN_SIZE) ||
> > +	    (priv->num != SPS30_SERIAL_FRAME_MIN_SIZE +
> > +	     priv->buf[SPS30_SERIAL_FRAME_MISO_LEN_OFFSET])) {
> > +		dev_err(state->dev, "frame has invalid number of bytes\n");
> > +		return false;
> > +	}
> > +
> > +	if ((priv->buf[SPS30_SERIAL_FRAME_ADR_OFFSET] != buf[SPS30_SERIAL_FRAME_ADR_OFFSET]) ||
> > +	    (priv->buf[SPS30_SERIAL_FRAME_CMD_OFFSET] != buf[SPS30_SERIAL_FRAME_CMD_OFFSET])) {
> > +		dev_err(state->dev, "frame has wrong ADR and CMD bytes\n");
> > +		return false;
> > +	}
> > +
> > +	if (priv->buf[SPS30_SERIAL_FRAME_MISO_STATE_OFFSET]) {
> > +		dev_err(state->dev, "frame with non-zero state received (0x%02x)\n",
> > +			priv->buf[SPS30_SERIAL_FRAME_MISO_STATE_OFFSET]);
> > +		//return false;
>
> ?
>
> > +	}
> > +
> > +	if (priv->buf[priv->num - 2] != priv->chksum) {
> > +		dev_err(state->dev, "frame integrity check failed\n");
> > +		return false;
> > +	}
> > +
> > +	return true;
> > +}
> > +
> > +static int sps30_serial_command(struct sps30_state *state, char cmd, void *arg, int arg_size,
> > +				void *rsp, int rsp_size)
> > +{
> > +	struct sps30_serial_priv *priv = state->priv;
> > +	char buf[SPS30_SERIAL_MAX_BUF_SIZE];
> > +	int ret, size;
> > +
> > +	size = sps30_serial_prep_frame(buf, cmd, arg, arg_size);
> > +	ret = sps30_serial_xfer(state, buf, size);
> > +	if (ret)
> > +		return ret;
> > +
> > +	if (!sps30_serial_frame_valid(state, buf))
> > +		return -EIO;
> > +
> > +	if (rsp) {
> > +		rsp_size = clamp((int)priv->buf[SPS30_SERIAL_FRAME_MISO_LEN_OFFSET], 0, rsp_size);
> > +		memcpy(rsp, &priv->buf[SPS30_SERIAL_FRAME_MISO_DATA_OFFSET], rsp_size);
> > +	}
> > +
> > +	return rsp_size;
> > +}
> > +
> > +static int sps30_serial_receive_buf(struct serdev_device *serdev, const unsigned char *buf,
> > +				    size_t size)
> > +{
> > +	struct iio_dev *indio_dev = dev_get_drvdata(&serdev->dev);
> > +	struct sps30_serial_priv *priv;
> > +	struct sps30_state *state;
> > +	unsigned char byte;
> > +	int i;
> > +
> > +	if (!indio_dev)
> > +		return 0;
> > +
> > +	state = iio_priv(indio_dev);
> > +	priv = state->priv;
> > +
> > +	/* just in case device put some unexpected data on the bus */
> > +	if (priv->done)
> > +		return size;
> > +
> > +	/* wait for the start of frame */
> > +	if (!priv->num && size && buf[0] != SPS30_SERIAL_SOF_EOF)
> > +		return 1;
> > +
> > +	if (priv->num + size >= ARRAY_SIZE(priv->buf))
> > +		size = ARRAY_SIZE(priv->buf) - priv->num;
> > +
> > +	for (i = 0; i < size; i++) {
> > +		byte = buf[i];
> > +		/* remove stuffed bytes on-the-fly */
> > +		if (byte == SPS30_SERIAL_ESCAPE_CHAR) {
> > +			priv->escaped = true;
> > +			continue;
> > +		}
> > +
> > +		byte = sps30_serial_get_byte(priv->escaped, byte);
> > +		if (priv->escaped && !byte)
> > +			dev_warn(state->dev, "unrecognized escaped char (0x%02x)\n", byte);
> > +		priv->chksum += byte;
> > +		/* incrementing here would complete rx just after reading SOF */
> > +		priv->buf[priv->num] = byte;
> > +
> > +		if (priv->num++ && !priv->escaped && byte == SPS30_SERIAL_SOF_EOF) {
> > +			/* SOF, EOF and checksum itself are not checksummed */
> > +			priv->chksum -= 2 * SPS30_SERIAL_SOF_EOF + priv->buf[priv->num - 2];
> > +			priv->chksum = (unsigned char)~priv->chksum;
> > +			priv->done = true;
> > +			complete(&priv->new_frame);
> > +			i++;
> > +			break;
> > +		}
> > +
> > +		priv->escaped = false;
> > +	}
> > +
> > +	return i;
> > +}
> > +
> > +static const struct serdev_device_ops sps30_serial_device_ops = {
> > +	.receive_buf = sps30_serial_receive_buf,
> > +	.write_wakeup = serdev_device_write_wakeup,
> > +};
> > +
> > +static int sps30_serial_start_meas(struct sps30_state *state)
> > +{
> > +	/* request BE IEEE754 formatted data */
> > +	char buf[] = { 0x01, 0x03 };
> > +
> > +	return sps30_serial_command(state, SPS30_SERIAL_START_MEAS, buf, sizeof(buf), NULL, 0);
> > +}
> > +
> > +static int sps30_serial_stop_meas(struct sps30_state *state)
> > +{
> > +	return sps30_serial_command(state, SPS30_SERIAL_STOP_MEAS, NULL, 0, NULL, 0);
> > +}
> > +
> > +static int sps30_serial_reset(struct sps30_state *state)
> > +{
> > +	int ret;
> > +
> > +	ret = sps30_serial_command(state, SPS30_SERIAL_RESET, NULL, 0, NULL, 0);
> > +	msleep(500);
> > +
> > +	return ret;
> > +}
> > +
> > +static int sps30_serial_read_meas(struct sps30_state *state, int *meas, int num)
> > +{
> > +	int ret, tries = 3;
> > +
>
> For any repeat loops like this, please add a comment to explain why you picked 3
> retries.  (it works is a valid comment, but obviously datasheet reference is better :)
>

According to the spec sensor spits out data each second but sometimes it
looks as if they are available in 500ms or so. Picking 3 for the number of
tries covers two cases.

> > +	do {
> > +		ret = sps30_serial_command(state, SPS30_SERIAL_READ_MEAS, NULL, 0,
> > +					   meas, num * sizeof(num));
> > +		if (ret < 0)
> > +			return ret;
> > +		/* if measurements aren't ready sensor returns empty frame */
> > +		if (ret == num * sizeof(int))
> > +			break;
> > +
> > +		if (msleep_interruptible(500))
> > +			return -EINTR;
> > +	} while (--tries);
> > +
> > +	return !tries ? -ETIMEDOUT : 0;
> > +}
> > +
> > +static int sps30_serial_clean_fan(struct sps30_state *state)
> > +{
> > +	return sps30_serial_command(state, SPS30_SERIAL_CLEAN_FAN, NULL, 0, NULL, 0);
> > +}
> > +
> > +static int sps30_serial_read_cleaning_period(struct sps30_state *state, int *period)
> > +{
> > +	char buf[] = { 0x00 };
> > +	int ret;
> > +
> > +	ret = sps30_serial_command(state, SPS30_SERIAL_PERIOD, buf, sizeof(buf),
> > +				   period, sizeof(*period));
> > +	if (ret < 0)
> > +		return ret;
> > +	if (ret != sizeof(*period))
> > +		return -EIO;
> > +
> > +	return 0;
> > +}
> > +
> > +static int sps30_serial_write_cleaning_period(struct sps30_state *state, int period)
> > +{
> > +	char buf[5] = { 0x00 };
> > +
> > +	memcpy(buf + 1, &period, sizeof(period));
>
> Same issue with what size period could in theory be. Also should be no problem keeping
> it in the __be32 type throughout.
>
> > +
> > +	return sps30_serial_command(state, SPS30_SERIAL_PERIOD, buf, sizeof(buf), NULL, 0);
> > +}
> > +
> > +static int sps30_serial_show_info(struct sps30_state *state)
> > +{
> > +	/* extra nul byte just in case serial number isn't a valid string */
> > +	char buf[32 + 1] = { 0x00 };
> > +	struct device *dev = state->dev;
> > +	int ret;
> > +
> > +	/* tell device to return serial number */
> > +	buf[0] = 0x03;
> > +	ret = sps30_serial_command(state, SPS30_SERIAL_DEV_INFO, buf, 1, buf, sizeof(buf) - 1);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	dev_info(dev, "serial number: %s\n", buf);
> > +
> > +	ret = sps30_serial_command(state, SPS30_SERIAL_READ_VERSION, NULL, 0, buf, sizeof(buf) - 1);
> > +	if (ret < 0)
> > +		return ret;
> > +	if (ret < 2)
> > +		return -EIO;
> > +
> > +	dev_info(dev, "fw version: %u.%u\n", buf[0], buf[1]);
> > +
> > +	return 0;
> > +}
> > +
> > +static const struct sps30_ops sps30_serial_ops = {
> > +	.start_meas = sps30_serial_start_meas,
> > +	.stop_meas = sps30_serial_stop_meas,
> > +	.read_meas = sps30_serial_read_meas,
> > +	.reset = sps30_serial_reset,
> > +	.clean_fan = sps30_serial_clean_fan,
> > +	.read_cleaning_period = sps30_serial_read_cleaning_period,
> > +	.write_cleaning_period = sps30_serial_write_cleaning_period,
> > +	.show_info = sps30_serial_show_info,
> > +};
> > +
> > +static int sps30_serial_probe(struct serdev_device *serdev)
> > +{
> > +	struct device *dev = &serdev->dev;
> > +	struct sps30_serial_priv *priv;
> > +	int ret;
> > +
> > +	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> > +	if (!priv)
> > +		return -ENOMEM;
> > +
> > +	init_completion(&priv->new_frame);
> > +	serdev_device_set_client_ops(serdev, &sps30_serial_device_ops);
> > +
> > +	ret = devm_serdev_device_open(dev, serdev);
> > +	if (ret)
> > +		return ret;
> > +
> > +	serdev_device_set_baudrate(serdev, 115200);
> > +	serdev_device_set_flow_control(serdev, false);
> > +
> > +	ret = serdev_device_set_parity(serdev, SERDEV_PARITY_NONE);
> > +	if (ret)
> > +		return ret;
> > +
> > +	return sps30_probe(dev, KBUILD_MODNAME, priv, &sps30_serial_ops);
> > +}
> > +
> > +static const struct of_device_id sps30_serial_of_match[] = {
> > +	{ .compatible = "sensirion,sps30" },
> > +	{ }
> > +};
> > +MODULE_DEVICE_TABLE(of, sps30_serial_of_match);
> > +
> > +static struct serdev_device_driver sps30_serial_driver = {
> > +	.driver = {
> > +		.name = KBUILD_MODNAME,
> > +		.of_match_table = sps30_serial_of_match,
> > +	},
> > +	.probe = sps30_serial_probe,
> > +};
> > +module_serdev_device_driver(sps30_serial_driver);
> > +
> > +MODULE_AUTHOR("Tomasz Duszynski <tomasz.duszynski@...akon.com>");
> > +MODULE_DESCRIPTION("Sensirion SPS30 particulate matter sensor serial driver");
> > +MODULE_LICENSE("GPL v2");
>

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