Date:	Mon, 19 Oct 2015 17:34:00 +0300
From:	Teodora Baluta <teodora.baluta@...el.com>
To:	Peter Meerwald <pmeerw@...erw.net>
Cc:	jic23@...nel.org, knaack.h@....de, lars@...afoo.de,
	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 Mon, Oct 19, 2015 at 01:08:50PM +0200, Peter Meerwald wrote:
> On Fri, 16 Oct 2015, 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.
> 
> minor comments below
> link to datasheet?

The datasheet is not public. I've asked Memsic if they can make the
datasheet public or if we can distribute a private copy on request.

I'll address the comments in the v2 patch. Thanks for the review!

>  
> > Signed-off-by: Teodora Baluta <teodora.baluta@...el.com>
> > ---
> >  drivers/iio/accel/Kconfig   |  11 +++
> >  drivers/iio/accel/Makefile  |   1 +
> >  drivers/iio/accel/mxc6255.c | 210 ++++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 222 insertions(+)
> >  create mode 100644 drivers/iio/accel/mxc6255.c
> > 
> > diff --git a/drivers/iio/accel/Kconfig b/drivers/iio/accel/Kconfig
> > index 969428d..75ac087 100644
> > --- a/drivers/iio/accel/Kconfig
> > +++ b/drivers/iio/accel/Kconfig
> > @@ -158,6 +158,17 @@ config MXC4005
> >  	  To compile this driver as a module, choose M. The module will be
> >  	  called mxc4005.
> >  
> > +config MXC6255
> > +	tristate "Memsic MXC6255 Orientation Sensing Accelerometer Driver"
> > +	depends on I2C
> > +	select REGMAP_I2C
> > +	help
> > +	  Say yes here to build support for the Memsic MXC6255 Orientation
> > +	  Sensing Accelerometer Driver.
> > +
> > +	  To compile this driver as a module, choose M here: the module will be
> > +	  called mxc6255.
> > +
> >  config STK8312
> >  	tristate "Sensortek STK8312 3-Axis Accelerometer Driver"
> >  	depends on I2C
> > diff --git a/drivers/iio/accel/Makefile b/drivers/iio/accel/Makefile
> > index 7925f16..525ed52 100644
> > --- a/drivers/iio/accel/Makefile
> > +++ b/drivers/iio/accel/Makefile
> > @@ -17,6 +17,7 @@ obj-$(CONFIG_MMA9551)		+= mma9551.o
> >  obj-$(CONFIG_MMA9553)		+= mma9553.o
> >  
> >  obj-$(CONFIG_MXC4005)		+= mxc4005.o
> > +obj-$(CONFIG_MXC6255)		+= mxc6255.o
> >  
> >  obj-$(CONFIG_STK8312)		+= stk8312.o
> >  obj-$(CONFIG_STK8BA50)		+= stk8ba50.o
> > diff --git a/drivers/iio/accel/mxc6255.c b/drivers/iio/accel/mxc6255.c
> > new file mode 100644
> > index 0000000..ed0f1ab
> > --- /dev/null
> > +++ b/drivers/iio/accel/mxc6255.c
> > @@ -0,0 +1,210 @@
> > +/*
> > + * MXC6255 - MEMSIC orientation sensing accelerometer
> > + *
> > + * Copyright (c) 2015, Intel Corporation.
> > + *
> > + * This file is subject to the terms and conditions of version 2 of
> > + * the GNU General Public License.  See the file COPYING in the main
> > + * directory of this archive for more details.
> > + *
> > + * IIO driver for MXC6255 (7-bit I2C slave address 0x15).
> > + *
> > + */
> > +
> > +#include <linux/module.h>
> > +#include <linux/i2c.h>
> > +#include <linux/init.h>
> > +#include <linux/iio/iio.h>
> > +#include <linux/delay.h>
> > +#include <linux/acpi.h>
> > +#include <linux/regmap.h>
> > +#include <linux/iio/sysfs.h>
> > +
> > +#define MXC6255_DRV_NAME		"mxc6255"
> > +#define MXC6255_REGMAP_NAME		"mxc6255_regmap"
> > +
> > +#define MXC6255_REG_XOUT		0x00
> > +#define MXC6255_REG_YOUT		0x01
> > +#define MXC6255_REG_CHIP_ID		0x08
> > +
> > +#define MXC6255_AXIS_TO_REG(axis)	(MXC6255_REG_XOUT + axis)
> > +
> > +/*
> > + * MXC6255 has only one measurement range: +/- 2G.
> > + * The acceleration output is an 8-bit value.
> 
> is a

I think it came from "an eight-bit value", so "is an" sounds right to
me.

> 
> > + *
> > + * Scale is calculated as following:
> 
> as follows
> 
> > + * (2 + 2) * 9.80665 / (2^8 - 1) = 0.153829
> > + *
> > + */
> > +#define MXC6255_SCALE_AVAIL		"0.153829"
> > +
> > +enum mxc6255_axis {
> > +	AXIS_X,
> > +	AXIS_Y,
> > +};
> > +
> > +struct mxc6255_data {
> > +	struct i2c_client *client;
> > +	struct regmap *regmap;
> > +};
> > +
> > +/* scale value for +/- 2G measurement range */
> > +static const int mxc6255_scale = 153829;
> 
> it is customary to use a #define
> 
> > +
> > +static IIO_CONST_ATTR(in_accel_scale_available, MXC6255_SCALE_AVAIL);
> > +
> > +static struct attribute *mxc6255_attributes[] = {
> > +	&iio_const_attr_in_accel_scale_available.dev_attr.attr,
> > +	NULL,
> > +};
> > +
> > +static const struct attribute_group mxc6255_attribute_group = {
> > +	.attrs = mxc6255_attributes
> > +};
> > +
> > +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;
> > +	int ret;
> > +
> > +	switch (mask) {
> > +	case IIO_CHAN_INFO_RAW:
> > +		ret = regmap_read(data->regmap,
> > +				  MXC6255_AXIS_TO_REG(axis), &reg);
> 
> use chan->address, and drop the _AXIS_TO_REG macro and axis variable
> 
> > +		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 const struct iio_info mxc6255_info = {
> > +	.driver_module	= THIS_MODULE,
> > +	.read_raw	= mxc6255_read_raw,
> > +	.attrs		= &mxc6255_attribute_group,
> > +};
> > +
> > +#define MXC6255_CHANNEL(_axis) {				\
> > +	.type = IIO_ACCEL,					\
> > +	.modified = 1,						\
> > +	.channel2 = IIO_MOD_##_axis,				\
> > +	.address = AXIS_##_axis,				\
> 
> put MXC6255_REG_XOUT / MXC6255_REG_YOUT here, add parameter to _CHANNEL 
> macro
> 
> > +	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
> > +	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),	\
> > +}
> > +
> > +static const struct iio_chan_spec mxc6255_channels[] = {
> > +	MXC6255_CHANNEL(X),
> > +	MXC6255_CHANNEL(Y),
> > +};
> > +
> > +static bool mxc6255_is_readable_reg(struct device *dev, unsigned int reg)
> > +{
> > +	switch (reg) {
> > +	case MXC6255_REG_XOUT:
> > +	case MXC6255_REG_YOUT:
> > +	case MXC6255_REG_CHIP_ID:
> > +		return true;
> > +	default:
> > +		return false;
> > +	}
> > +}
> > +
> > +static const struct regmap_config mxc6255_regmap_config = {
> > +	.name = MXC6255_REGMAP_NAME,
> > +
> > +	.reg_bits = 8,
> > +	.val_bits = 8,
> > +
> > +	.readable_reg = mxc6255_is_readable_reg,
> > +};
> > +
> > +static int mxc6255_probe(struct i2c_client *client,
> > +			 const struct i2c_device_id *id)
> > +{
> > +	struct mxc6255_data *data;
> > +	struct iio_dev *indio_dev;
> > +	struct regmap *regmap;
> > +	unsigned int chip_id;
> > +	int ret;
> > +
> > +	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
> > +	if (!indio_dev)
> > +		return -ENOMEM;
> > +
> > +	regmap = devm_regmap_init_i2c(client, &mxc6255_regmap_config);
> > +	if (IS_ERR(regmap)) {
> > +		dev_err(&client->dev, "Error initializing regmap\n");
> > +		return PTR_ERR(regmap);
> > +	}
> > +
> > +	data = iio_priv(indio_dev);
> > +	i2c_set_clientdata(client, indio_dev);
> > +	data->client = client;
> > +	data->regmap = regmap;
> > +
> > +	indio_dev->name = MXC6255_DRV_NAME;
> > +	indio_dev->dev.parent = &client->dev;
> > +	indio_dev->channels = mxc6255_channels;
> > +	indio_dev->num_channels = ARRAY_SIZE(mxc6255_channels);
> > +	indio_dev->modes = INDIO_DIRECT_MODE;
> > +	indio_dev->info = &mxc6255_info;
> > +
> > +	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;
> > +	}
> > +
> > +	dev_dbg(&client->dev, "Chip id %x\n", chip_id);
> 
> maybe check chip id?

Will do.

> 
> > +
> > +	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;
> > +}
> > +
> > +static const struct acpi_device_id mxc6255_acpi_match[] = {
> > +	{"MXC6255",	0},
> > +	{ }
> > +};
> > +MODULE_DEVICE_TABLE(acpi, mxc6255_acpi_match);
> > +
> > +static const struct i2c_device_id mxc6255_id[] = {
> > +	{"mxc6255",	0},
> > +	{ }
> > +};
> > +MODULE_DEVICE_TABLE(i2c, mxc6255_id);
> > +
> > +static struct i2c_driver mxc6255_driver = {
> > +	.driver = {
> > +		.name = MXC6255_DRV_NAME,
> > +		.acpi_match_table = ACPI_PTR(mxc6255_acpi_match),
> > +	},
> > +	.probe		= mxc6255_probe,
> > +	.id_table	= mxc6255_id,
> > +};
> > +
> > +module_i2c_driver(mxc6255_driver);
> > +
> > +MODULE_AUTHOR("Teodora Baluta <teodora.baluta@...el.com>");
> > +MODULE_DESCRIPTION("MEMSIC MXC6255 orientation sensing accelerometer driver");
> > +MODULE_LICENSE("GPL v2");
> > 
> 
> -- 
> 
> Peter Meerwald
> +43-664-2444418 (mobile)
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