Message-ID: <4C8275FB.7080509@cam.ac.uk>
Date:	Sat, 04 Sep 2010 17:38:19 +0100
From:	Jonathan Cameron <jic23@....ac.uk>
To:	achew@...dia.com
CC:	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
	linux-i2c@...r.kernel.org, akpm@...ux-foundation.org,
	khali@...ux-fr.org, ldewangan@...dia.com
Subject: Re: [PATCH 1/1] iio: ak8975: Add Ak8975 magnetometer sensor

On 09/03/10 00:40, achew@...dia.com wrote:
> From: Andrew Chew <achew@...dia.com>
> 
> This is for the Asahi Kasei AK8975 3-axis magnetometer.  It resides within
> the magnetometer section of the IIO subsystem, and implements the raw
> magn_x,y,z attributes, as well as x,y,z factory calibration attributes.
> 
> Signed-off-by: Andrew Chew <achew@...dia.com>

Hi Andrew,

Looks pretty clean.  A nice little driver.

Anyhow inline you will find:

* A few nitpicking points about eating errors. Lots of drivers in
  kernel do it, but lets not encourage even more.
* Couple of other cleanup suggestions (none of which are vital, but
  might be worth doing if you are respinning anyway)  I'm particularly
  intrigued to know if the sannity check for existence of the device
  can ever fail...

I'll take a final look after you have done the abi related changes.

Thanks,

Jonathan

p.s. As Andrew said, please make it clear which version of a patch
this is, typically make the subject [Patch 1/1 V2] iio: ak8975 ...
And some brief comments to say what has changed from the previous
version are a great time saver for reviewers.


> ---
>  drivers/staging/iio/magnetometer/Kconfig  |   11 +
>  drivers/staging/iio/magnetometer/Makefile |    1 +
>  drivers/staging/iio/magnetometer/ak8975.c |  521 +++++++++++++++++++++++++++++
>  3 files changed, 533 insertions(+), 0 deletions(-)
>  create mode 100644 drivers/staging/iio/magnetometer/ak8975.c
> 
> diff --git a/drivers/staging/iio/magnetometer/Kconfig b/drivers/staging/iio/magnetometer/Kconfig
> index d014450..00e1204 100644
> --- a/drivers/staging/iio/magnetometer/Kconfig
> +++ b/drivers/staging/iio/magnetometer/Kconfig
> @@ -3,6 +3,17 @@
>  #
>  comment "Magnetometer sensors"
>  
> +config SENSORS_AK8975
> +	tristate "Asahi Kasei AK8975 3-Axis Magnetometer"
> +	default n
> +	depends on I2C
> +	help
> +	  Say yes here to build support for Asahi Kasei AK8975 3-Axis
> +	  Magnetometer.
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called ak8975.
> +
>  config SENSORS_HMC5843
>  	tristate "Honeywell HMC5843 3-Axis Magnetometer"
>  	depends on I2C
> diff --git a/drivers/staging/iio/magnetometer/Makefile b/drivers/staging/iio/magnetometer/Makefile
> index f9bfb2e..e3dbaa4 100644
> --- a/drivers/staging/iio/magnetometer/Makefile
> +++ b/drivers/staging/iio/magnetometer/Makefile
> @@ -2,4 +2,5 @@
>  # Makefile for industrial I/O Magnetometer sensors
>  #
>  
> +obj-$(CONFIG_SENSORS_AK8975)	:= ak8975.o
>  obj-$(CONFIG_SENSORS_HMC5843)	+= hmc5843.o
> diff --git a/drivers/staging/iio/magnetometer/ak8975.c b/drivers/staging/iio/magnetometer/ak8975.c
> new file mode 100644
> index 0000000..ca39840
> --- /dev/null
> +++ b/drivers/staging/iio/magnetometer/ak8975.c
> @@ -0,0 +1,521 @@
> +/*
> + * A sensor driver for the magnetometer AK8975.
> + *
> + * Magnetic compass sensor driver for monitoring magnetic flux information.
> + *
> + * Copyright (c) 2010, NVIDIA Corporation.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along
> + * with this program; if not, write to the Free Software Foundation, Inc.,
> + * 51 Franklin Street, Fifth Floor, Boston, MA	02110-1301, USA.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/kernel.h>
> +#include <linux/slab.h>
> +#include <linux/i2c.h>
> +#include <linux/err.h>
> +#include <linux/mutex.h>
> +#include <linux/delay.h>
> +
> +#include <linux/gpio.h>
> +
> +#include "../iio.h"
> +#include "magnet.h"
> +
> +/*
> + * Register definitions, as well as various shifts and masks to get at the
> + * individual fields of the registers.
> + */
> +#define AK8975_REG_WIA			0x00
> +#define AK8975_DEVICE_ID		0x48
> +
> +#define AK8975_REG_INFO			0x01
> +
> +#define AK8975_REG_ST1			0x02
> +#define AK8975_REG_ST1_DRDY_SHIFT	0
> +#define AK8975_REG_ST1_DRDY_MASK	(1 << AK8975_REG_ST1_DRDY_SHIFT)
> +
> +#define AK8975_REG_HXL			0x03
> +#define AK8975_REG_HXH			0x04
> +#define AK8975_REG_HYL			0x05
> +#define AK8975_REG_HYH			0x06
> +#define AK8975_REG_HZL			0x07
> +#define AK8975_REG_HZH			0x08
> +#define AK8975_REG_ST2			0x09
> +#define AK8975_REG_ST2_DERR_SHIFT	2
> +#define AK8975_REG_ST2_DERR_MASK	(1 << AK8975_REG_ST2_DERR_SHIFT)
> +
> +#define AK8975_REG_ST2_HOFL_SHIFT	3
> +#define AK8975_REG_ST2_HOFL_MASK	(1 << AK8975_REG_ST2_HOFL_SHIFT)
> +
> +#define AK8975_REG_CNTL			0x0A
> +#define AK8975_REG_CNTL_MODE_SHIFT	0
> +#define AK8975_REG_CNTL_MODE_MASK	(0xF << AK8975_REG_CNTL_MODE_SHIFT)
> +#define AK8975_REG_CNTL_MODE_POWER_DOWN	0
> +#define AK8975_REG_CNTL_MODE_ONCE	1
> +#define AK8975_REG_CNTL_MODE_SELF_TEST	8
> +#define AK8975_REG_CNTL_MODE_FUSE_ROM	0xF
> +
> +#define AK8975_REG_RSVC			0x0B
> +#define AK8975_REG_ASTC			0x0C
> +#define AK8975_REG_TS1			0x0D
> +#define AK8975_REG_TS2			0x0E
> +#define AK8975_REG_I2CDIS		0x0F
> +#define AK8975_REG_ASAX			0x10
> +#define AK8975_REG_ASAY			0x11
> +#define AK8975_REG_ASAZ			0x12
> +
> +#define AK8975_MAX_REGS			AK8975_REG_ASAZ
> +
> +/*
> + * Miscellaneous values.
> + */
> +#define AK8975_MAX_CONVERSION_TRIAL	5
> +#define AK8975_MAX_CONVERSION_TIMEOUT	500
> +#define AK8975_CONVERSION_DONE_POLL_TIME 10
> +
> +/*
> + * Per-instance context data for the device.
> + */
> +struct ak8975_data {
> +	struct i2c_client	*client;
> +	struct iio_dev		*indio_dev;
> +	struct attribute_group  attrs;
> +	struct mutex            lock;
> +	u8                      asa[3];
> +	unsigned long           mode;
> +	u8                      reg_cache[AK8975_MAX_REGS];
> +	int                     eoc_gpio;
> +	int                     eoc_irq;
> +};
> +
> +/*
> + * Helper function to write to the I2C device's registers.
> + */
> +static bool ak8975_write_data(struct i2c_client *client,
> +			      u8 reg, u8 val, u8 mask, u8 shift)
> +{
> +	u8 regval;
> +	struct i2c_msg msg;
> +	u8 w_data[2];
> +	int ret = 0;
> +
> +	struct ak8975_data *data = i2c_get_clientdata(client);
> +
> +	regval = data->reg_cache[reg];
> +	regval &= ~mask;
> +	regval |= val << shift;
> +
> +	w_data[0] = reg;
> +	w_data[1] = regval;
> +
> +	msg.addr = client->addr;
> +	msg.flags = 0;
> +	msg.len = 2;
> +	msg.buf = w_data;
> +
> +	ret = i2c_transfer(client->adapter, &msg, 1);
> +	if (ret < 0) {
> +		dev_err(&client->dev, "Write to device fails status %x\n", ret);
> +		return false;
> +	}
> +	data->reg_cache[reg] = regval;
> +
> +	return true;
> +}
> +
> +/*
> + * Helper function to read a contiguous set of the I2C device's registers.
> + */
> +static bool ak8975_read_data(struct i2c_client *client,
> +			     u8 reg, u8 length, u8 *buffer)
> +{
> +	struct i2c_msg msg[2];
> +	u8 w_data[2];
> +	int ret = 0;
> +
> +	w_data[0] = reg;
> +
> +	msg[0].addr = client->addr;
> +	msg[0].flags = I2C_M_NOSTART;	/* set repeated start and write */
> +	msg[0].len = 1;
> +	msg[0].buf = w_data;
> +
> +	msg[1].addr = client->addr;
> +	msg[1].flags = I2C_M_RD;
> +	msg[1].len = length;
> +	msg[1].buf = buffer;
> +
> +	ret = i2c_transfer(client->adapter, msg, 2);
> +	if (ret < 0) {
> +		dev_err(&client->dev, "Read from device fails\n");
> +		return false;
Ideally you would pass on the actual error code here. Sometimes i2c_transfer
will give more information than simply that it failed.
> +	}
> +
> +	return true;
> +}
> +
> +/*
> + * Perform some start-of-day setup, including reading the asa calibration
> + * values and caching them.
> + */
> +static int ak8975_setup(struct i2c_client *client)
> +{
> +	struct ak8975_data *data = i2c_get_clientdata(client);
> +	u8 device_id;
> +	u8 buffer[3];
> +	bool status;
> +
> +	/* Confirm that the device we're talking to is really an AK8975. */
> +	status = ak8975_read_data(client, AK8975_REG_WIA, 1, &device_id);
> +	if ((!status) || (device_id != AK8975_DEVICE_ID)) {
> +		dev_err(&client->dev, "Device ak8975 not found\n");
That's not necessarily the right error. If you had passed on the result
of the i2c_transfter in ak8975_read_data we might have something more specific.
> +		return -ENODEV;
> +	}
> +
> +	/* Write the fused rom access mode. */
> +	status = ak8975_write_data(client,
> +				   AK8975_REG_CNTL,
> +				   AK8975_REG_CNTL_MODE_FUSE_ROM,
> +				   AK8975_REG_CNTL_MODE_MASK,
> +				   AK8975_REG_CNTL_MODE_SHIFT);
> +	if (!status) {
> +		dev_err(&client->dev, "Error in setting fuse access mode\n");
Same point as above.  The underlying code can in theory produce a number of
errors. It's always best to pass up as much information as possible.
> +		return -EINVAL;
> +	}
> +
> +	/* Get asa data and store in the device data. */
> +	status = ak8975_read_data(client, AK8975_REG_ASAX, 3, buffer);
> +	if (!status) {
> +		dev_err(&client->dev, "Not able to read asa data\n");
> +		return -EINVAL;
> +	}
> +
Why do you need & 0xFF, buffer is a u8 so I don't see how any other bits
could be set? I think you could just read directly into data->asa and
skip these copies entirely.
> +	data->asa[0] = buffer[0] & 0xFF;
> +	data->asa[1] = buffer[1] & 0xFF;
> +	data->asa[2] = buffer[2] & 0xFF;
> +
> +	return 0;
> +}
> +
> +/*
> + * Shows the device's mode.  0 = off, 1 = on.
> + */
> +static ssize_t show_mode(struct device *dev, struct device_attribute *devattr,
> +			 char *buf)
> +{
> +	struct iio_dev *indio_dev = dev_get_drvdata(dev);
> +	struct ak8975_data *data = indio_dev->dev_data;
> +
Using an unsigned long for something that is a boolean value seems a little
unusual... I guess this was to simplify the next function, but simply copying
the unsigned long there into a boolean for the tests would be more conventional.

> +	return sprintf(buf, "%lu\n", data->mode);
> +}
> +
> +/*
> + * Sets the device's mode.  0 = off, 1 = on.  The device's mode must be on
> + * for the magn raw attributes to be available.
> + */
> +static ssize_t store_mode(struct device *dev, struct device_attribute *devattr,
> +			  const char *buf, size_t count)
> +{
> +	struct iio_dev *indio_dev = dev_get_drvdata(dev);
> +	struct ak8975_data *data = indio_dev->dev_data;
> +	struct i2c_client *client = data->client;
> +	unsigned long oval;
> +	bool status;
> +
> +	/* Convert mode string and do some basic sanity checking on it.
> +	   only 0 or 1 are valid. */
> +	if (strict_strtoul(buf, 10, &oval))
> +		return -EINVAL;
> +
> +	if (oval > 1) {
> +		dev_err(dev, "mode value is not supported\n");
> +		return -EINVAL;
> +	}
> +
> +	mutex_lock(&data->lock);
> +
> +	/* Write the mode to the device. */
> +	if (data->mode != oval) {
> +		status = ak8975_write_data(client,
> +					   AK8975_REG_CNTL,
> +					   (u8)oval,
> +					   AK8975_REG_CNTL_MODE_MASK,
> +					   AK8975_REG_CNTL_MODE_SHIFT);
> +
> +		if (!status) {
> +			dev_err(&client->dev, "Error in setting mode\n");
> +			mutex_unlock(&data->lock);
> +			return -EINVAL;
> +		}
> +		data->mode = oval;
> +	}
> +
> +	mutex_unlock(&data->lock);
> +
> +	return count;
> +}
> +
> +/*
> + * Emits the ASA sensitivity adjustment value for the x, y, or z axis.
> + * These ASA values are read from the sensor device at start of day, and
> + * cached in the device context struct.
> + */
> +static ssize_t show_calibscale(struct device *dev,
> +			       struct device_attribute *devattr, char *buf)
> +{
> +	struct iio_dev *indio_dev = dev_get_drvdata(dev);
> +	struct ak8975_data *data = indio_dev->dev_data;
> +	struct iio_dev_attr *this_attr = to_iio_dev_attr(devattr);
> +
I think this sanity check is overkill.  If there were no device, then the attribute
should never have been pushed.  Have you managed to cause this to ever happen?
> +	if (!data) {
> +		dev_err(dev, "No device found\n");
> +		return -ENODEV;
> +	}
> +
> +	return sprintf(buf, "%d\n", data->asa[this_attr->address]);
> +}
> +
> +/*
> + * Emits the raw flux value for the x, y, or z axis.
> + *
> + * Adjusting the flux value with the sensitivity adjustment value should be
> + * done via the following formula:
> + *
> + * Hadj = H * ( ( ( (ASA-128)*0.5 ) / 128 ) + 1 )
> + *
> + * where H is the raw value, ASA is the sensitivity adjustment, and Hadj
> + * is the resultant adjusted value.
> + */
> +static ssize_t show_raw(struct device *dev, struct device_attribute *devattr,
> +			char *buf)
> +{
> +	struct iio_dev *indio_dev = dev_get_drvdata(dev);
> +	struct ak8975_data *data = indio_dev->dev_data;
> +	struct i2c_client *client = data->client;
> +	struct iio_dev_attr *this_attr = to_iio_dev_attr(devattr);
> +	u32 timeout_ms = AK8975_MAX_CONVERSION_TIMEOUT;
> +	u16 meas_reg;
> +	s16 raw;
> +	u8 read_status;
> +	bool status;
> +	int state;
> +
> +	/* Set up the device for taking a sample. */
> +	status = ak8975_write_data(client,
> +				   AK8975_REG_CNTL,
> +				   AK8975_REG_CNTL_MODE_ONCE,
> +				   AK8975_REG_CNTL_MODE_MASK,
> +				   AK8975_REG_CNTL_MODE_SHIFT);
> +	if (!status) {
> +		dev_err(&client->dev, "Error in setting operating mode\n");
> +		return -EINVAL;
> +	}
> +
> +	/* Wait for the conversion to complete. */
> +	while (timeout_ms) {
> +		msleep(AK8975_CONVERSION_DONE_POLL_TIME);
> +		state = (gpio_get_value(data->eoc_gpio) ? 1 : 0);
This is fine, but personally I'm in favour of,
state = !!gpio_get_value(data->eoc_gpio) which should do the same thing.

Why not just replace the if statement with
if (gpio_get_value(data->eoc_gpio))  - we don't need to enforce the 0 or 1
if we are going to use it like this.

> +		if (state)
> +			break;
> +		timeout_ms -= AK8975_CONVERSION_DONE_POLL_TIME;
> +	}
> +	if (!timeout_ms) {
> +		dev_err(&client->dev, "Conversion timeout happend\n");
> +		return -EINVAL;
> +	}
> +
> +	status = ak8975_read_data(client, AK8975_REG_ST1, 1, &read_status);
> +	if (!status) {
> +		dev_err(&client->dev, "Error in reading ST1\n");
> +		return -EINVAL;
> +	}
> +
> +	if (read_status & AK8975_REG_ST1_DRDY_MASK) {
> +		status = ak8975_read_data(client, AK8975_REG_ST2,
> +					  1, &read_status);
> +		if (!status) {
> +			dev_err(&client->dev, "Error in reading ST2\n");
> +			return -EINVAL;
> +		}
> +		if (read_status & (AK8975_REG_ST2_DERR_MASK |
> +				   AK8975_REG_ST2_HOFL_MASK)) {
> +			dev_err(&client->dev, "ST2 status error 0x%x\n",
> +				read_status);
> +			return -EINVAL;
> +		}
> +	}
> +
> +	/* Read the flux value from the appropriate register
> +	   (the register is specified in the iio device attributes). */
> +	status = ak8975_read_data(client, this_attr->address, 2,
> +				  (u8 *)&meas_reg);
> +	if (!status) {
> +		dev_err(&client->dev, "Read axis data fails\n");
> +		return -EINVAL;
> +	}
> +
> +	/* Endian conversion of the measured values */
> +	raw = (s16) (le16_to_cpu(meas_reg));
> +
> +	return sprintf(buf, "%d\n", raw);
> +}
> +
> +static IIO_DEVICE_ATTR(mode, S_IRUGO | S_IWUSR, show_mode, store_mode, 0);
> +static IIO_DEVICE_ATTR(magn_x_calibscale, S_IRUGO, show_calibscale, NULL, 0);
> +static IIO_DEVICE_ATTR(magn_y_calibscale, S_IRUGO, show_calibscale, NULL, 1);
> +static IIO_DEVICE_ATTR(magn_z_calibscale, S_IRUGO, show_calibscale, NULL, 2);
> +static IIO_DEV_ATTR_MAGN_X(show_raw, AK8975_REG_HXL);
> +static IIO_DEV_ATTR_MAGN_Y(show_raw, AK8975_REG_HYL);
> +static IIO_DEV_ATTR_MAGN_Z(show_raw, AK8975_REG_HZL);
> +
> +static struct attribute *ak8975_attr[] = {
> +	&iio_dev_attr_mode.dev_attr.attr,
> +	&iio_dev_attr_magn_x_calibscale.dev_attr.attr,
> +	&iio_dev_attr_magn_y_calibscale.dev_attr.attr,
> +	&iio_dev_attr_magn_z_calibscale.dev_attr.attr,
> +	&iio_dev_attr_magn_x_raw.dev_attr.attr,
> +	&iio_dev_attr_magn_y_raw.dev_attr.attr,
> +	&iio_dev_attr_magn_z_raw.dev_attr.attr,
> +	NULL
> +};
> +
> +static struct attribute_group ak8975_attr_group = {
> +	.attrs = ak8975_attr,
> +};
> +
> +static int ak8975_probe(struct i2c_client *client,
> +			const struct i2c_device_id *id)
> +{
> +	struct ak8975_data *data;
> +	int err;
> +
> +	/* Allocate our device context. */
> +	data = kzalloc(sizeof(struct ak8975_data), GFP_KERNEL);
> +	if (!data) {
> +		dev_err(&client->dev, "Memory allocation fails\n");
> +		err = -ENOMEM;
> +		goto exit;
> +	}
> +
> +	i2c_set_clientdata(client, data);
> +	data->client = client;
> +
> +	mutex_init(&data->lock);
> +
> +	/* Grab and set up the supplied GPIO. */
> +	data->eoc_irq = client->irq;
> +	data->eoc_gpio = irq_to_gpio(client->irq);
> +
> +	if (!data->eoc_gpio) {
> +		dev_err(&client->dev, "failed, no valid GPIO\n");
> +		goto exit_free;
> +	}
> +
> +	err = gpio_request(data->eoc_gpio, "ak_8975");
> +	if (err < 0) {
> +		dev_err(&client->dev, "failed to request GPIO %d, error %d\n",
> +			data->eoc_gpio, err);
> +		goto exit_free;
> +	}
> +
> +	err = gpio_direction_input(data->eoc_gpio);
> +	if (err < 0) {
> +		dev_err(&client->dev, "Failed to configure input direction for"
> +			" GPIO %d, error %d\n", data->eoc_gpio, err);
> +		goto exit_gpio;
> +	}
> +
> +	/* Perform some basic start-of-day setup of the device. */
> +	err = ak8975_setup(client);
> +	if (err < 0) {
> +		dev_err(&client->dev, "AK8975 initialization fails\n");
> +		goto exit_gpio;
> +	}
> +
> +	/* Register with IIO */
> +	data->indio_dev = iio_allocate_device();
> +	if (data->indio_dev == NULL) {
> +		err = -ENOMEM;
> +		goto exit_gpio;
> +	}
> +
> +	data->indio_dev->dev.parent = &client->dev;
> +	data->indio_dev->attrs = &ak8975_attr_group;
> +	data->indio_dev->dev_data = (void *)(data);
> +	data->indio_dev->driver_module = THIS_MODULE;
> +	data->indio_dev->modes = INDIO_DIRECT_MODE;
> +
> +	err = iio_device_register(data->indio_dev);
> +	if (err < 0)
> +		goto exit_free_iio;
> +
> +	return 0;
> +
> +exit_free_iio:
> +	iio_free_device(data->indio_dev);
> +exit_gpio:
> +	gpio_free(data->eoc_gpio);
> +exit_free:
> +	kfree(data);
> +exit:
> +	return err;
> +}
> +
> +static int ak8975_remove(struct i2c_client *client)
> +{
> +	struct ak8975_data *data = i2c_get_clientdata(client);
> +
> +	iio_device_unregister(data->indio_dev);
> +	iio_free_device(data->indio_dev);
> +
> +	gpio_free(data->eoc_gpio);
> +
> +	kfree(data);
> +
> +	return 0;
> +}
> +
> +static const struct i2c_device_id ak8975_id[] = {
> +	{"ak8975", 0},
> +	{}
> +};
> +
> +MODULE_DEVICE_TABLE(i2c, ak8975_id);
> +
> +static struct i2c_driver ak8975_driver = {
> +	.driver = {
> +		.name	= "ak8975",
> +	},
> +	.probe		= ak8975_probe,
> +	.remove		= __devexit_p(ak8975_remove),
> +	.id_table	= ak8975_id,
> +};
> +
> +static int __init ak8975_init(void)
> +{
> +	return i2c_add_driver(&ak8975_driver);
> +}
> +
> +static void __exit ak8975_exit(void)
> +{
> +	i2c_del_driver(&ak8975_driver);
> +}
> +
> +module_init(ak8975_init);
> +module_exit(ak8975_exit);
> +
> +MODULE_AUTHOR("Laxman Dewangan <ldewangan@...dia.com>");
> +MODULE_DESCRIPTION("AK8975 magnetometer driver");
> +MODULE_LICENSE("GPL");

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