linux-kernel - Re: [PATCH] iio: accel: add support for Memsic MXC6255XC sensor

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Date:	Mon, 19 Oct 2015 12:52:50 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Teodora Baluta <teodora.baluta@...el.com>, jic23@...nel.org
CC:	knaack.h@....de, pmeerw@...erw.net, daniel.baluta@...el.com,
	dan.carpenter@...cle.com, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: accel: add support for Memsic MXC6255XC sensor

On 10/16/2015 12:29 PM, Teodora Baluta wrote:
> This patch adds a minimal implementation for the Memsic MXC6255XC
> orientation sensing accelerometer. The supported operations are reading
> raw acceleration values for X/Y axis that can be scaled using the
> exposed scale.
> 
> Signed-off-by: Teodora Baluta <teodora.baluta@...el.com>

Looks quite good in general, a few minor things inline.

[...]
> +/* scale value for +/- 2G measurement range */
> +static const int mxc6255_scale = 153829;
> +
> +static IIO_CONST_ATTR(in_accel_scale_available, MXC6255_SCALE_AVAIL);

If there is only one scale available it does not make too much sense to have
a scale_available attribute.

[..]
> +static int mxc6255_read_raw(struct iio_dev *indio_dev,
> +			    struct iio_chan_spec const *chan,
> +			    int *val, int *val2, long mask)
> +{
> +	struct mxc6255_data *data = iio_priv(indio_dev);
> +	unsigned int reg;
> +	int axis = chan->channel2 - 1;

1 is a bit of a magic constant here. Use IIO_MOD_X instead. Or even better
use chan->address.

> +	int ret;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		ret = regmap_read(data->regmap,
> +				  MXC6255_AXIS_TO_REG(axis), &reg);
> +		if (ret < 0) {
> +			dev_err(&data->client->dev,
> +				"Error reading axis %d\n", axis);
> +			return ret;
> +		}
> +
> +		*val = sign_extend32(reg, 7);
> +		return IIO_VAL_INT;
> +	case IIO_CHAN_INFO_SCALE:
> +		*val = 0;
> +		*val2 = mxc6255_scale;
> +		return IIO_VAL_INT_PLUS_MICRO;
> +	default:
> +		return -EINVAL;
> +	}
> +}
[...]
> +static int mxc6255_probe(struct i2c_client *client,
> +			 const struct i2c_device_id *id)
> +{
[...]
> +	ret = regmap_read(data->regmap, MXC6255_REG_CHIP_ID, &chip_id);
> +	if (ret < 0) {
> +		dev_err(&client->dev, "Error reading chip id %d\n", ret);
> +		return ret;
> +	}

Does it make sense to check whether chip ID matches the expected value, to
catch mistakes where the I2C address is incorrect?

> +
> +	dev_dbg(&client->dev, "Chip id %x\n", chip_id);
> +
> +	ret = devm_iio_device_register(&client->dev, indio_dev);
> +	if (ret < 0) {
> +		dev_err(&client->dev, "Could not register IIO device\n");
> +		return ret;
> +	}
> +
> +	return 0;
> +}
[...]
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