Date:   Mon, 26 Nov 2018 21:48:07 +0100
From:   Tomasz Duszynski <tduszyns@...il.com>
To:     Himanshu Jha <himanshujha199640@...il.com>
Cc:     Tomasz Duszynski <tduszyns@...il.com>, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 2/3] iio: chemical: add support for Sensirion SPS30 sensor

On Sun, Nov 25, 2018 at 04:14:34PM +0530, Himanshu Jha wrote:
> On Sat, Nov 24, 2018 at 11:14:14PM +0100, Tomasz Duszynski wrote:
> > Add support for Sensirion SPS30 particulate matter sensor.
> >
> > Signed-off-by: Tomasz Duszynski <tduszyns@...il.com>
> > ---
> >  drivers/iio/chemical/Kconfig  |  11 ++
> >  drivers/iio/chemical/Makefile |   1 +
> >  drivers/iio/chemical/sps30.c  | 359 ++++++++++++++++++++++++++++++++++
> >  3 files changed, 371 insertions(+)
> >  create mode 100644 drivers/iio/chemical/sps30.c
>
> []
>
> > +#define pr_fmt(fmt) "sps30: " fmt
>
> I don't see its usage ?
>

Hint: checkout how dev_err() is defined.

> > +#include <linux/crc8.h>
> > +#include <linux/delay.h>
> > +#include <linux/i2c.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/module.h>
> > +
> > +#define SPS30_CRC8_POLYNOMIAL 0x31
> > +
> > +/* SPS30 commands */
> > +#define SPS30_START_MEAS 0x0010
> > +#define SPS30_STOP_MEAS 0x0104
> > +#define SPS30_RESET 0xd304
> > +#define SPS30_READ_DATA_READY_FLAG 0x0202
> > +#define SPS30_READ_DATA 0x0300
> > +#define SPS30_READ_SERIAL 0xD033
>
> Could you please put a tab and align these macros.
>
>   #define SPS30_START_MEAS		0x0010
>   #define SPS30_STOP_MEAS		0x0104
>

In my opinion this sort of alignment does not pay off in the long run.
Adding a new definition, a slightly longer one perhaps, can easily break
formatting.

So I would stay with current one.

>
> > +static int sps30_write_then_read(struct sps30_state *state, u8 *buf,
> > +				 int buf_size, u8 *data, int data_size)
> > +{
> > +	/* every two received data bytes are checksummed */
> > +	u8 tmp[data_size + data_size / 2];
>
> No VLAs!
>
> https://lore.kernel.org/lkml/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com/
>

Looks like -Wvla is some fairly recent addition to KBUILD_CFLAGS.

> > +	int ret, i;
> > +
> > +	/*
> > +	 * Sensor does not support repeated start so instead of
> > +	 * sending two i2c messages in a row we just send one by one.
> > +	 */
> > +	ret = i2c_master_send(state->client, buf, buf_size);
> > +	if (ret != buf_size)
> > +		return ret < 0 ? ret : -EIO;
> > +
> > +	if (!data)
> > +		return 0;
> > +
> > +	ret = i2c_master_recv(state->client, tmp, sizeof(tmp));
> > +	if (ret != sizeof(tmp))
> > +		return ret < 0 ? ret : -EIO;
> > +
> > +	for (i = 0; i < sizeof(tmp); i += 3) {
> > +		u8 crc = crc8(sps30_crc8_table, &tmp[i], 2, CRC8_INIT_VALUE);
> > +
> > +		if (crc != tmp[i + 2]) {
> > +			dev_err(&state->client->dev,
> > +				"data integrity check failed\n");
> > +			return -EIO;
> > +		}
> > +
> > +		*data++ = tmp[i];
> > +		*data++ = tmp[i + 1];
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int sps30_do_cmd(struct sps30_state *state, u16 cmd, u8 *data, int size)
> > +{
> > +	/* depending on the command up to 3 bytes may be needed for argument */
> > +	u8 buf[sizeof(cmd) + 3] = { cmd >> 8, cmd };
>
> This is fine, since sizeof returns constant integer expression.
>
> > +	switch (cmd) {
> > +	case SPS30_START_MEAS:
> > +		buf[2] = 0x03;
> > +		buf[3] = 0x00;
> > +		buf[4] = 0xac; /* precomputed crc */
> > +		return sps30_write_then_read(state, buf, 5, NULL, 0);
> > +	case SPS30_STOP_MEAS:
> > +	case SPS30_RESET:
> > +		return sps30_write_then_read(state, buf, 2, NULL, 0);
> > +	case SPS30_READ_DATA_READY_FLAG:
> > +	case SPS30_READ_DATA:
> > +	case SPS30_READ_SERIAL:
> > +		return sps30_write_then_read(state, buf, 2, data, size);
> > +	default:
> > +		return -EINVAL;
> > +	};
> > +}
>
>
> > +static int sps30_read_raw(struct iio_dev *indio_dev,
> > +			  struct iio_chan_spec const *chan,
> > +			  int *val, int *val2, long mask)
> > +{
> > +	struct sps30_state *state = iio_priv(indio_dev);
> > +	int ret;
> > +
> > +	switch (mask) {
> > +	case IIO_CHAN_INFO_PROCESSED:
> > +		switch (chan->type) {
> > +		case IIO_MASSCONCENTRATION:
> > +			mutex_lock(&state->lock);
> > +			switch (chan->channel2) {
> > +			case IIO_MOD_PM2p5:
>
> I think lock should be placed here
>
> > +				ret = sps30_do_meas(state, val, val2);
>
> ... and unlock here.
>
> > +				break;
> > +			case IIO_MOD_PM10:
> > +				ret = sps30_do_meas(state, val2, val);
> > +				break;
> > +			default:
> > +				break;
> > +			}
> > +			mutex_unlock(&state->lock);
> > +			if (ret)
> > +				return ret;
> > +
> > +			return IIO_VAL_INT;
> > +		default:
> > +			return -EINVAL;
> > +		}
> > +		break;
> > +	default:
> > +		return -EINVAL;
> > +	}
> > +}
>
> []
>
> > +static int sps30_probe(struct i2c_client *client)
> > +{
> > +	struct iio_dev *indio_dev;
> > +	struct sps30_state *state;
> > +	u8 buf[32] = { };
>
> This is not valid in ISO-C but only in C++.
>
> Instead,
>
> 	u8 buf[32] = {0};
>
> > +	int ret;
> > +
> > +	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
> > +		return -EOPNOTSUPP;
> > +
> > +	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*state));
> > +	if (!indio_dev)
> > +		return -ENOMEM;
> > +
> > +	state = iio_priv(indio_dev);
> > +	i2c_set_clientdata(client, indio_dev);
> > +	state->client = client;
> > +	indio_dev->dev.parent = &client->dev;
> > +	indio_dev->info = &sps30_info;
> > +	indio_dev->name = client->name;
> > +	indio_dev->channels = sps30_channels;
> > +	indio_dev->num_channels = ARRAY_SIZE(sps30_channels);
> > +	indio_dev->modes = INDIO_DIRECT_MODE;
> > +	indio_dev->available_scan_masks = sps30_scan_masks;
> > +
> > +	mutex_init(&state->lock);
> > +	crc8_populate_msb(sps30_crc8_table, SPS30_CRC8_POLYNOMIAL);
> > +
> > +	/*
> > +	 * Power-on-reset causes sensor to produce some glitch on i2c bus
> > +	 * and some controllers end up in error state. Recover simply
> > +	 * by placing something on the bus.
> > +	 */
> > +	ret = sps30_do_cmd(state, SPS30_RESET, NULL, 0);
> > +	if (ret) {
> > +		dev_err(&client->dev, "failed to reset device\n");
> > +		return ret;
> > +	}
> > +	usleep_range(2500000, 3500000);
>
> Isn't that range too high ?
> msleep_interruptible ?
>

Might be.

> > +	sps30_do_cmd(state, SPS30_STOP_MEAS, NULL, 0);
> > +
> > +	ret = sps30_do_cmd(state, SPS30_READ_SERIAL, buf, sizeof(buf));
> > +	if (ret) {
> > +		dev_err(&client->dev, "failed to read serial number\n");
> > +		return ret;
> > +	}
> > +	dev_info(&client->dev, "serial number: %s\n", buf);
> > +
> > +	ret = sps30_do_cmd(state, SPS30_START_MEAS, NULL, 0);
> > +	if (ret) {
> > +		dev_err(&client->dev, "failed to start measurement\n");
> > +		return ret;
> > +	}
> > +
> > +	ret = devm_iio_triggered_buffer_setup(&client->dev, indio_dev, NULL,
> > +					      sps30_trigger_handler, NULL);
> > +	if (ret)
> > +		return ret;
> > +
> > +	return devm_iio_device_register(&client->dev, indio_dev);
> > +}
> > +
> > +static int sps30_remove(struct i2c_client *client)
>
> Perfect candidate for `devm_add_action_or_reset()` ?
>
> > +{
> > +	struct iio_dev *indio_dev = i2c_get_clientdata(client);
> > +	struct sps30_state *state = iio_priv(indio_dev);
> > +
> > +	sps30_do_cmd(state, SPS30_STOP_MEAS, NULL, 0);
> > +
> > +	return 0;
> > +}
>
>
> --
> Himanshu Jha
> Undergraduate Student
> Department of Electronics & Communication
> Guru Tegh Bahadur Institute of Technology

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