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Date:   Sun, 31 May 2020 17:50:01 +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>, <robh+dt@...nel.org>,
        <andy.shevchenko@...il.com>, <pmeerw@...erw.net>
Subject: Re: [PATCH v2 3/4] iio: chemical: scd30: add serial interface driver

On Sun, May 31, 2020 at 11:15:18AM +0100, Jonathan Cameron wrote:
> On Sat, 30 May 2020 23:36:29 +0200
> Tomasz Duszynski <tomasz.duszynski@...akon.com> wrote:
>
> > Add serial interface driver for the SCD30 sensor.
> >
> > Signed-off-by: Tomasz Duszynski <tomasz.duszynski@...akon.com>
>
> Ah Now I see why you had those extra elements in the iio_priv
> structure.
>

Indeed. That the whole point of having them. I'll add a short
explanation what those elements are for.

> Hmm. serdev_device callbacks using the top level device drvdata
> is a bit annoying.  Really feels to me like they should have
> their own priv data for those callbacks given the device
> drvdata gets used for so many other things.
>
> Oh well. Guess this is the best we can do!
>
> Jonathan
>
> > ---
> >  MAINTAINERS                         |   1 +
> >  drivers/iio/chemical/Kconfig        |  11 ++
> >  drivers/iio/chemical/Makefile       |   1 +
> >  drivers/iio/chemical/scd30_serial.c | 266 ++++++++++++++++++++++++++++
> >  4 files changed, 279 insertions(+)
> >  create mode 100644 drivers/iio/chemical/scd30_serial.c
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 13aed3473b7e..5db4b446c8ba 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -15143,6 +15143,7 @@ S:	Maintained
> >  F:	drivers/iio/chemical/scd30.h
> >  F:	drivers/iio/chemical/scd30_core.c
> >  F:	drivers/iio/chemical/scd30_i2c.c
> > +F:	drivers/iio/chemical/scd30_serial.c
> >
> >  SENSIRION SPS30 AIR POLLUTION SENSOR DRIVER
> >  M:	Tomasz Duszynski <tduszyns@...il.com>
> > diff --git a/drivers/iio/chemical/Kconfig b/drivers/iio/chemical/Kconfig
> > index 970d34888c2e..10bb431bc3ce 100644
> > --- a/drivers/iio/chemical/Kconfig
> > +++ b/drivers/iio/chemical/Kconfig
> > @@ -107,6 +107,17 @@ config SCD30_I2C
> >  	  To compile this driver as a module, choose M here: the module will
> >  	  be called scd30_i2c.
> >
> > +config SCD30_SERIAL
> > +	tristate "SCD30 carbon dioxide sensor serial driver"
> > +	depends on SCD30_CORE && SERIAL_DEV_BUS
> > +	select CRC16
> > +	help
> > +	  Say Y here to build support for the Sensirion SCD30 serial interface
> > +	  driver.
> > +
> > +	  To compile this driver as a module, choose M here: the module will
> > +	  be called scd30_serial.
> > +
> >  config SENSIRION_SGP30
> >  	tristate "Sensirion SGPxx gas sensors"
> >  	depends on I2C
> > diff --git a/drivers/iio/chemical/Makefile b/drivers/iio/chemical/Makefile
> > index 0966ca34e34b..fef63dd5bf92 100644
> > --- a/drivers/iio/chemical/Makefile
> > +++ b/drivers/iio/chemical/Makefile
> > @@ -14,6 +14,7 @@ obj-$(CONFIG_IAQCORE)		+= ams-iaq-core.o
> >  obj-$(CONFIG_PMS7003) += pms7003.o
> >  obj-$(CONFIG_SCD30_CORE) += scd30_core.o
> >  obj-$(CONFIG_SCD30_I2C) += scd30_i2c.o
> > +obj-$(CONFIG_SCD30_SERIAL) += scd30_serial.o
> >  obj-$(CONFIG_SENSIRION_SGP30)	+= sgp30.o
> >  obj-$(CONFIG_SPS30) += sps30.o
> >  obj-$(CONFIG_VZ89X)		+= vz89x.o
> > diff --git a/drivers/iio/chemical/scd30_serial.c b/drivers/iio/chemical/scd30_serial.c
> > new file mode 100644
> > index 000000000000..07d7d3110fe0
> > --- /dev/null
> > +++ b/drivers/iio/chemical/scd30_serial.c
> > @@ -0,0 +1,266 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Sensirion SCD30 carbon dioxide sensor serial driver
> > + *
> > + * Copyright (c) 2020 Tomasz Duszynski <tomasz.duszynski@...akon.com>
> > + */
> > +#include <linux/crc16.h>
> > +#include <linux/device.h>
> > +#include <linux/errno.h>
> > +#include <linux/iio/iio.h>
> > +#include <linux/jiffies.h>
> > +#include <linux/mod_devicetable.h>
> > +#include <linux/module.h>
> > +#include <linux/property.h>
> > +#include <linux/serdev.h>
> > +#include <linux/string.h>
> > +#include <linux/types.h>
> > +#include <asm/unaligned.h>
> > +
> > +#include "scd30.h"
> > +
> > +#define SCD30_SERDEV_ADDR 0x61
> > +#define SCD30_SERDEV_WRITE 0x06
> > +#define SCD30_SERDEV_READ 0x03
> > +#define SCD30_SERDEV_MAX_BUF_SIZE 17
> > +#define SCD30_SERDEV_RX_HEADER_SIZE 3
> > +#define SCD30_SERDEV_CRC_SIZE 2
> > +#define SCD30_SERDEV_TIMEOUT msecs_to_jiffies(200)
> > +
> > +struct scd30_serdev_priv {
> > +	struct completion meas_ready;
> > +	char *buf;
> > +	int num_expected;
> > +	int num;
> > +};
> > +
> > +static u16 scd30_serdev_cmd_lookup_tbl[] = {
> > +	[CMD_START_MEAS] = 0x0036,
> > +	[CMD_STOP_MEAS] = 0x0037,
> > +	[CMD_MEAS_INTERVAL] = 0x0025,
> > +	[CMD_MEAS_READY] = 0x0027,
> > +	[CMD_READ_MEAS] = 0x0028,
> > +	[CMD_ASC] = 0x003a,
> > +	[CMD_FRC] = 0x0039,
> > +	[CMD_TEMP_OFFSET] = 0x003b,
> > +	[CMD_FW_VERSION] = 0x0020,
> > +	[CMD_RESET] = 0x0034,
> > +};
> > +
> > +static u16 scd30_serdev_calc_crc(const char *buf, int size)
> > +{
> > +	return crc16(0xffff, buf, size);
> > +}
> > +
> > +static int scd30_serdev_xfer(struct scd30_state *state, char *txbuf, int txsize,
> > +			     char *rxbuf, int rxsize)
> > +{
> > +	struct serdev_device *serdev = to_serdev_device(state->dev);
> > +	struct scd30_serdev_priv *priv = state->priv;
> > +	int ret;
> > +
> > +	priv->buf = rxbuf;
> > +	priv->num_expected = rxsize;
> > +	priv->num = 0;
> > +
> > +	ret = serdev_device_write(serdev, txbuf, txsize, SCD30_SERDEV_TIMEOUT);
> > +	if (ret < txsize)
> > +		return ret < 0 ? ret : -EIO;
> > +
> > +	ret = wait_for_completion_interruptible_timeout(&priv->meas_ready,
> > +							SCD30_SERDEV_TIMEOUT);
> > +	if (ret > 0)
> > +		ret = 0;
> > +	else if (!ret)
> > +		ret = -ETIMEDOUT;
> > +
> > +	return ret;
> > +}
> > +
> > +static int scd30_serdev_command(struct scd30_state *state, enum scd30_cmd cmd,
> > +				u16 arg, void *response, int size)
> > +{
> > +	/*
> > +	 * Communication over serial line is based on modbus protocol (or rather
> > +	 * its variation called modbus over serial to be precise). Upon
> > +	 * receiving a request device should reply with response.
> > +	 *
> > +	 * Frame below represents a request message. Each field takes
> > +	 * exactly one byte.
> > +	 *
> > +	 * +------+------+-----+-----+-------+-------+-----+-----+
> > +	 * | dev  | op   | reg | reg | byte1 | byte0 | crc | crc |
> > +	 * | addr | code | msb | lsb |       |       | lsb | msb |
> > +	 * +------+------+-----+-----+-------+-------+-----+-----+
> > +	 *
> > +	 * The message device replies with depends on the 'op code' field from
> > +	 * the request. In case it was set to SCD30_SERDEV_WRITE sensor should
> > +	 * reply with unchanged request. Otherwise 'op code' was set to
> > +	 * SCD30_SERDEV_READ and response looks like the one below. As with
> > +	 * request, each field takes one byte.
> > +	 *
> > +	 * +------+------+--------+-------+-----+-------+-----+-----+
> > +	 * | dev  | op   | num of | byte0 | ... | byteN | crc | crc |
> > +	 * | addr | code | bytes  |       |     |       | lsb | msb |
> > +	 * +------+------+--------+-------+-----+-------+-----+-----+
> > +	 */
> > +	char txbuf[SCD30_SERDEV_MAX_BUF_SIZE] = { SCD30_SERDEV_ADDR },
> > +	     rxbuf[SCD30_SERDEV_MAX_BUF_SIZE], *rsp = response;
> > +	int ret, rxsize, txsize = 2;
> > +	u16 crc;
> > +
> > +	put_unaligned_be16(scd30_serdev_cmd_lookup_tbl[cmd], txbuf + txsize);
> > +	txsize += 2;
> > +
> > +	if (rsp) {
> > +		txbuf[1] = SCD30_SERDEV_READ;
> > +		if (cmd == CMD_READ_MEAS)
> > +			/* number of u16 words to read */
> > +			put_unaligned_be16(size / 2, txbuf + txsize);
> > +		else
> > +			put_unaligned_be16(0x0001, txbuf + txsize);
> > +		txsize += 2;
> > +		crc = scd30_serdev_calc_crc(txbuf, txsize);
> > +		put_unaligned_le16(crc, txbuf + txsize);
> > +		txsize += 2;
> > +		rxsize = SCD30_SERDEV_RX_HEADER_SIZE + size +
> > +			 SCD30_SERDEV_CRC_SIZE;
> > +	} else {
> > +		if ((cmd == CMD_STOP_MEAS) || (cmd == CMD_RESET))
> > +			arg = 0x0001;
> > +
> > +		txbuf[1] = SCD30_SERDEV_WRITE;
> > +		put_unaligned_be16(arg, txbuf + txsize);
> > +		txsize += 2;
> > +		crc = scd30_serdev_calc_crc(txbuf, txsize);
> > +		put_unaligned_le16(crc, txbuf + txsize);
> > +		txsize += 2;
> > +		rxsize = txsize;
> > +	}
> > +
> > +	ret = scd30_serdev_xfer(state, txbuf, txsize, rxbuf, rxsize);
> > +	if (ret)
> > +		return ret;
> > +
> > +	switch (txbuf[1]) {
> > +	case SCD30_SERDEV_WRITE:
> > +		if (memcmp(txbuf, txbuf, txsize)) {
> > +			dev_err(state->dev, "wrong message received\n");
> > +			return -EIO;
> > +		}
> > +		break;
> > +	case SCD30_SERDEV_READ:
> > +		if (rxbuf[2] != (rxsize -
> > +				 SCD30_SERDEV_RX_HEADER_SIZE -
> > +				 SCD30_SERDEV_CRC_SIZE)) {
> > +			dev_err(state->dev,
> > +				"received data size does not match header\n");
> > +			return -EIO;
> > +		}
> > +
> > +		rxsize -= SCD30_SERDEV_CRC_SIZE;
> > +		crc = get_unaligned_le16(rxbuf + rxsize);
> > +		if (crc != scd30_serdev_calc_crc(rxbuf, rxsize)) {
> > +			dev_err(state->dev, "data integrity check failed\n");
> > +			return -EIO;
> > +		}
> > +
> > +		rxsize -= SCD30_SERDEV_RX_HEADER_SIZE;
> > +		memcpy(rsp, rxbuf + SCD30_SERDEV_RX_HEADER_SIZE, rxsize);
> > +		break;
> > +	default:
> > +		dev_err(state->dev, "received unknown op code\n");
> > +		return -EIO;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int scd30_serdev_receive_buf(struct serdev_device *serdev,
> > +				    const unsigned char *buf, size_t size)
> > +{
> > +	struct iio_dev *indio_dev = dev_get_drvdata(&serdev->dev);
> > +	struct scd30_serdev_priv *priv;
> > +	struct scd30_state *state;
> > +	int num;
> > +
> > +	if (!indio_dev)
> > +		return 0;
> > +
> > +	state = iio_priv(indio_dev);
> > +	priv = state->priv;
> > +
> > +	/* just in case sensor puts some unexpected bytes on the bus */
> > +	if (!priv->buf)
> > +		return 0;
> > +
> > +	if (priv->num + size >= priv->num_expected)
> > +		num = priv->num_expected - priv->num;
> > +	else
> > +		num = size;
> > +
> > +	memcpy(priv->buf + priv->num, buf, num);
> > +	priv->num += num;
> > +
> > +	if (priv->num == priv->num_expected) {
> > +		priv->buf = NULL;
> > +		complete(&priv->meas_ready);
> > +	}
> > +
> > +	return num;
> > +}
> > +
> > +static const struct serdev_device_ops scd30_serdev_ops = {
> > +	.receive_buf = scd30_serdev_receive_buf,
> > +	.write_wakeup = serdev_device_write_wakeup,
> > +};
> > +
> > +static int scd30_serdev_probe(struct serdev_device *serdev)
> > +{
> > +	struct device *dev = &serdev->dev;
> > +	struct scd30_serdev_priv *priv;
> > +	int irq, ret;
> > +
> > +	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> > +	if (!priv)
> > +		return -ENOMEM;
> > +
> > +	init_completion(&priv->meas_ready);
> > +	serdev_device_set_client_ops(serdev, &scd30_serdev_ops);
> > +
> > +	ret = devm_serdev_device_open(dev, serdev);
> > +	if (ret)
> > +		return ret;
> > +
> > +	serdev_device_set_baudrate(serdev, 19200);
> > +	serdev_device_set_flow_control(serdev, false);
> > +
> > +	ret = serdev_device_set_parity(serdev, SERDEV_PARITY_NONE);
> > +	if (ret)
> > +		return ret;
> > +
> > +	irq = fwnode_irq_get(dev_fwnode(dev), 0);
> > +
> > +	return scd30_probe(dev, irq, KBUILD_MODNAME, priv,
> > +			   scd30_serdev_command);
> > +}
> > +
> > +static const struct of_device_id scd30_serdev_of_match[] = {
> > +	{ .compatible = "sensirion,scd30" },
> > +	{ }
> > +};
> > +MODULE_DEVICE_TABLE(of, scd30_serdev_of_match);
> > +
> > +static struct serdev_device_driver scd30_serdev_driver = {
> > +	.driver = {
> > +		.name = KBUILD_MODNAME,
> > +		.of_match_table = scd30_serdev_of_match,
> > +		.pm = &scd30_pm_ops,
> > +	},
> > +	.probe = scd30_serdev_probe,
> > +};
> > +module_serdev_device_driver(scd30_serdev_driver);
> > +
> > +MODULE_AUTHOR("Tomasz Duszynski <tomasz.duszynski@...akon.com>");
> > +MODULE_DESCRIPTION("Sensirion SCD30 carbon dioxide sensor serial driver");
> > +MODULE_LICENSE("GPL v2");
>

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