linux-kernel - Re: [PATCH v3 3/4] drivers: iio: chemical: Add support for Sensirion SCD4x CO2 sensor

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Message-ID: <20210925172307.305be961@jic23-huawei>
Date:   Sat, 25 Sep 2021 17:23:07 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Roan van Dijk <roan@...tonic.nl>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Tomasz Duszynski <tomasz.duszynski@...akon.com>,
        linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, david@...tonic.nl,
        Lars-Peter Clausen <lars@...afoo.de>
Subject: Re: [PATCH v3 3/4] drivers: iio: chemical: Add support for
 Sensirion SCD4x CO2 sensor

On Wed, 22 Sep 2021 12:39:24 +0200
Roan van Dijk <roan@...tonic.nl> wrote:

> This is a driver for the SCD4x CO2 sensor from Sensirion. The sensor is
> able to measure CO2 concentration, temperature and relative humdity.
> The sensor uses a photoacoustic principle for measuring CO2 concentration.
> An I2C interface is supported by this driver in order to communicate with
> the sensor.
> 
> Signed-off-by: Roan van Dijk <roan@...tonic.nl>

Hi Roan,

Only thing in here of significance is that the format for available attribute
is wrong + it needs adding to the ABI docs.

Given we are going to have a v4, I noted a few other minor things to tidy up.

Thanks,

Jonathan


> +static int scd4x_read(struct scd4x_state *state, enum scd4x_cmd cmd,
> +			void *response, int response_sz)
> +{
> +	struct i2c_client *client = state->client;
> +	char buf[SCD4X_READ_BUF_SIZE];
> +	char *rsp = response;
> +	int i, ret;
> +	char crc;
> +
> +	/*
> +	 * Measurement needs to be stopped before sending commands.
> +	 * Except for reading measurement and data ready command.
> +	 */
> +	if ((cmd != CMD_GET_DATA_READY) && (cmd != CMD_READ_MEAS)) {
> +		ret = scd4x_send_command(state, CMD_STOP_MEAS);
> +		if (ret)
> +			return ret;
> +
> +		/* execution time for stopping measurement */
> +		msleep_interruptible(500);
> +	}
> +
> +	/*CRC byte for every 2 bytes of data */

/* CRC..

Please check for similar as otherwise we'll get 'cleanup' patches the moment various
scripts hit this new code and it'll waste our time!

> +	response_sz += response_sz / 2;
> +
> +	put_unaligned_be16(cmd, buf);
> +	ret = scd4x_i2c_xfer(state, buf, 2, buf, response_sz);
> +	if (ret)
> +		return ret;
> +
> +	for (i = 0; i < response_sz; i += 3) {
> +		crc = crc8(scd4x_crc8_table, buf + i, 2, CRC8_INIT_VALUE);
> +		if (crc != buf[i + 2]) {
> +			dev_err(&client->dev, "CRC error\n");
> +			return -EIO;
> +		}
> +
> +		*rsp++ = buf[i];
> +		*rsp++ = buf[i + 1];
> +	}
> +
> +	/* start measurement */
> +	if ((cmd != CMD_GET_DATA_READY) && (cmd != CMD_READ_MEAS)) {
> +		ret = scd4x_send_command(state, CMD_START_MEAS);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +

...

> +
> +static IIO_DEVICE_ATTR_RW(calibration_auto_enable, 0);
> +static IIO_DEVICE_ATTR_WO(calibration_forced_value, 0);
> +
> +static IIO_CONST_ATTR(calibration_forced_value_available,
> +	       __stringify(SCD4X_FRC_MIN_PPM 1 SCD4X_FRC_MAX_PPM));

Ah, I wasn't completely clear on this.  See the main ABI doc for
_available

Format for this needs to include brackets to indicate it's a range
rather than 3 numbers 
"[MIN 1  MAX]"


Having added this it also needs to be in the ABI documentation.
Whilst somewhat trivial, all ABI should be documented there.

> +
> +static struct attribute *scd4x_attrs[] = {
> +	&iio_dev_attr_calibration_auto_enable.dev_attr.attr,
> +	&iio_dev_attr_calibration_forced_value.dev_attr.attr,
> +	&iio_const_attr_calibration_forced_value_available.dev_attr.attr,
> +	NULL
> +};
> +
> +static const struct attribute_group scd4x_attr_group = {
> +	.attrs = scd4x_attrs,
> +};
> +
> +static const struct iio_info scd4x_info = {
> +	.attrs = &scd4x_attr_group,
> +	.read_raw = scd4x_read_raw,
> +	.write_raw = scd4x_write_raw,
> +};
> +

...

> +
> +static irqreturn_t scd4x_trigger_handler(int irq, void *p)
> +{
> +	struct iio_poll_func *pf = p;
> +	struct iio_dev *indio_dev = pf->indio_dev;
> +	struct scd4x_state *state = iio_priv(indio_dev);
> +	struct {
> +		uint16_t data[3];
> +		int64_t ts __aligned(8);
> +	} scan;
> +	int ret;
> +	uint16_t buf[3];
> +
> +	mutex_lock(&state->lock);
> +	ret = scd4x_read_poll(state, buf);
> +	mutex_unlock(&state->lock);
> +	if (ret)
> +		goto out;
> +
> +	memset(&scan, 0, sizeof(scan));
> +	memcpy(scan.data, buf, sizeof(buf));

I missed this before, but why not do the scd4x_read_poll() directly into scan->data after
you've done the memset?  That way you avoid the need for a memcpy.

i.e.

	memset(&scan, 0, sizeof(scan));
	mutex_lock(&state->lock)
	ret = scd4x_read_poll(state, scan->data);
	mutex_unlock(&state->lock);
	if (ret)
	...


> +
> +	iio_push_to_buffers_with_timestamp(indio_dev, &scan, iio_get_time_ns(indio_dev));
> +out:
> +	iio_trigger_notify_done(indio_dev->trig);
> +	return IRQ_HANDLED;
> +}
> +