drivers/input/misc/magwheel.c

/*
 *  magwheel.c - Linux kernel driver for the Diamond scroll wheel
 *   It uses the Freescale Vybrid vf610 ADC driver (iio/adc/vf610_adc.c) as a
 *	 template
 *
 * ==Requirements==
 *  This driver should read two voltages every 2ms or less. It should then:
 *  - center those values around 0
 *  - calculate current_angle = atan(val1/val2)
 *  - find the smallest change the wheel would have had to make to reflect that
 *	degree change.
 *  Assuming atan was in the range 0 to 360, 350 to 10 is a +20 degree
 *	change.
 *  10 to 350 is a -20 degree change (because a +340 degree change is
 *	larger, and so we don't pick that).
 *
 *  We can read the output of this to find the movement of the magwheel
 *
 * ==Notes on requirements==
 *  - The current_angle calculated above is calculating the direction of
 *	magnetic field
 *  - If we read voltages at longer intervals than 2ms, there's a danger that
 *	the user may spin the device fast enough to give us incorrect readings.
 *	In the assumption that "the smallest change is the real change", imagine
 *	if a user jumped from 10 to 350 degrees between the times that we
 *	polled. We would think they moved 20 degrees backwards. So we need to be
 *	sampling at greater than twice per period to understand what the user is
 *	doing (yay Nyquist)!
 *  - The atan calculation comes from the specsheet of the magnetic sensor
 *  - Centering values around 0 means shifting the readings
 *	by -(max_reading + min_reading) / 2.
 *
 *  Copyright (C) 2010 Nest Labs, Inc
 *
 *  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., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/interrupt.h>
#include <linux/delay.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/io.h>
#include <linux/clk.h>
#include <linux/completion.h>
#include <linux/of.h>
#include <linux/of_irq.h>
#include <linux/regulator/consumer.h>
#include <linux/of_platform.h>
#include <linux/err.h>
#include <linux/input-polldev.h>
#include <linux/bitops.h>
#include <linux/of_gpio.h>
#include <linux/gpio/consumer.h>

#include <linux/iio/iio.h>
#include <linux/iio/sysfs.h>
#include <linux/iio/driver.h>

/* This will be the driver name the kernel reports */
#define DRIVER_NAME "vf610-adc-magwheel"

/* Vybrid/IMX ADC registers */
#define VF610_REG_ADC_HC0		0x00
#define VF610_REG_ADC_HC1		0x04
#define VF610_REG_ADC_HS		0x08
#define VF610_REG_ADC_R0		0x0c
#define VF610_REG_ADC_R1		0x10
#define VF610_REG_ADC_CFG		0x14
#define VF610_REG_ADC_GC		0x18
#define VF610_REG_ADC_GS		0x1c
#define VF610_REG_ADC_CV		0x20
#define VF610_REG_ADC_OFS		0x24
#define VF610_REG_ADC_CAL		0x28
#define VF610_REG_ADC_PCTL		0x30

/* Configuration register field define */
#define VF610_ADC_MODE_BIT8		0x00
#define VF610_ADC_MODE_BIT10    0x04
#define VF610_ADC_MODE_BIT12	0x08
#define VF610_ADC_MODE_MASK		0x0c
#define VF610_ADC_BUSCLK_SEL	0x00
#define VF610_ADC_BUSCLK2_SEL	0x01
#define VF610_ADC_ALTCLK_SEL	0x02
#define VF610_ADC_ADACK_SEL		0x03
#define VF610_ADC_ADCCLK_MASK	0x03
#define VF610_ADC_CLK_DIV2		0x20
#define VF610_ADC_CLK_DIV4		0x40
#define VF610_ADC_CLK_DIV8		0x60
#define VF610_ADC_CLK_MASK		0x60
#define VF610_ADC_ADLSMP_LONG	0x10
#define VF610_ADC_ADSTS_MASK	0x300
#define VF610_ADC_ADLPC_EN		0x80
#define VF610_ADC_ADHSC_EN		0x400
#define VF610_ADC_REFSEL_VREF	0x0
#define VF610_ADC_REFSEL_VALT	0x100
#define VF610_ADC_REFSEL_VBG	0x1000
#define VF610_ADC_ADTRG_HARD	0x2000
#define VF610_ADC_AVGS_8		0x4000
#define VF610_ADC_AVGS_16		0x8000
#define VF610_ADC_AVGS_32		0xC000
#define VF610_ADC_AVGS_MASK		0xC000
#define VF610_ADC_OVWREN		0x10000

/* General control register field define */
#define VF610_ADC_ADACKEN		0x1
#define VF610_ADC_DMAEN			0x2
#define VF610_ADC_ACREN			0x4
#define VF610_ADC_ACFGT			0x8
#define VF610_ADC_ACFE			0x10
#define VF610_ADC_AVGEN			0x20
#define VF610_ADC_ADCON			0x40
#define VF610_ADC_CAL			0x80

/* Comparators */
#define VF610_ADC_ACFE          0x10
#define VF610_ADC_ACFGT         0x8
#define VF610_ADC_ACREN         0x4
#define VF610_ADC_CV1           0x0000FFF
#define VF610_ADC_CV2           0xFFF0000
#define VF610_ADC_CV2_SHIFT     16

/* Other field define */
#define VF610_ADC_ADCHC(x)		((x) & 0x1F)
#define VF610_ADC_AIEN			(0x1 << 7)
#define VF610_ADC_CONV_DISABLE	0x1F
#define VF610_ADC_HS_COCO0		0x1
#define VF610_ADC_CALF			0x2
#define VF610_ADC_TIMEOUT		msecs_to_jiffies(100)

/* For atan */
#define ATAN_HYPO_MULTIPLIER    5

#define BITS_MASK_12            0xFFF
#define MAX_ADC_VAL		0xFFF
#define MIN_ADC_VAL		0
#define MAX_INT                 0x7ffffff
#define COMPARATOR_WINDOW_INIT	10
#define ENABLE_DELAY_MIN_US	8000
#define ENABLE_DELAY_MAX_US	12000

#define VF610_ADC_CHAN(_idx, _chan_type) {			\
	.type = (_chan_type),					\
	.indexed = 1,						\
	.channel = (_idx),					\
	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
	.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) |  \
				BIT(IIO_CHAN_INFO_CALIBSCALE) | \
				BIT(IIO_CHAN_INFO_SAMP_FREQ),	\
}
static const struct iio_chan_spec vf610_adc_iio_channels[] = {
	VF610_ADC_CHAN(0, IIO_VOLTAGE),
	VF610_ADC_CHAN(1, IIO_VOLTAGE),
	VF610_ADC_CHAN(2, IIO_VOLTAGE),
	VF610_ADC_CHAN(3, IIO_VOLTAGE),
	VF610_ADC_CHAN(4, IIO_VOLTAGE),
	VF610_ADC_CHAN(5, IIO_VOLTAGE),
	VF610_ADC_CHAN(6, IIO_VOLTAGE),
	VF610_ADC_CHAN(7, IIO_VOLTAGE),
	VF610_ADC_CHAN(8, IIO_VOLTAGE),
	VF610_ADC_CHAN(9, IIO_VOLTAGE),
	VF610_ADC_CHAN(10, IIO_VOLTAGE),
	VF610_ADC_CHAN(11, IIO_VOLTAGE),
	VF610_ADC_CHAN(12, IIO_VOLTAGE),
	VF610_ADC_CHAN(13, IIO_VOLTAGE),
	VF610_ADC_CHAN(14, IIO_VOLTAGE),
	VF610_ADC_CHAN(15, IIO_VOLTAGE),
	/* sentinel */
};

#define ATAN_TABLE_SIZE 15
static int tan_table[ATAN_TABLE_SIZE] = {
	11520, 6801, 3593, 1824, 916, 458, 229,
	115, 57, 28, 14, 7, 4, 2, 1
};

/*
 * Given that work_handler is running at at most every 10 jiffies
 * (should normally be 2), and that the time between interrupts
 * is around 380 microseconds, each buffer channel length should be **132**.
 *
 * -- Derivation --
 * 2 jiffies = 20ms; 20ms / 380 microseconds = 52.
 *
 * That is, 52 interrupts happen before the delayed_work "buffer consumer" runs
 *
 * I've also tested this with no load and the largest length the sum
 * of the two buffers got to was 50.
 *
 * However, we won't be guaranteed delay_work hits exactly 2 jiffies;
 * it might be more delayed under high load.
 *
 * To be safe, let's say it might take up to 10 jiffies.
 * 100ms / 380 microseconds = 264. That's the sum of the buffers,
 * so each channel needs just half of that -- 132.
 *
 * So **132** should be the buffer length
 */
#define BUFFER_LENGTH 132
struct vf610_adc {
	struct device *dev;
	void __iomem *regs;
	struct clk *clk;

	u32 vref_uv;
	u32 value;
	struct regulator *vref;
	bool calibration;

	struct completion completion;

	int channel_index;
	u32 channels[2];
	u32 channel_midpoints[2];

	struct input_dev *input_dev;
	int irq;

	/* calibration values */
	int scale_int; /* integer component*/
	int scale_micro; /* thousandths component */
};

struct magwheel_work {
	struct delayed_work work;
	struct magwheel *mag_info;
};

struct magwheel {
	struct vf610_adc adc_info;
	struct iio_dev *indio_dev;

	/* The ADC resolution is 12 bits, so 16 bits is enough */
	int buffered_vals1[BUFFER_LENGTH];
	int buffered_vals2[BUFFER_LENGTH];
	int buffered_loc;
	int buffered_loc_last;
	int last_angle;
	int comparator_window;
	struct gpio_desc *enable_gpio;
	struct magwheel_work readbuffer_work;
};

static void magwheel_set_window(int center, struct magwheel *mag_info);
static void magwheel_single_conversion_start(struct vf610_adc *adc_info, int channel);
static void magwheel_continuous_conversion_start(struct vf610_adc *adc_info);

static void dump_regs(struct vf610_adc *adc_info){
	int HC0, HC1, HS, R0, R1, CFG, GC, GS, CV, OFS, CAL;

	HC0 = readl(adc_info->regs + VF610_REG_ADC_HC0);
	HC1 = readl(adc_info->regs + VF610_REG_ADC_HC1);
	HS = readl(adc_info->regs + VF610_REG_ADC_HS);
	R0 = readl(adc_info->regs + VF610_REG_ADC_R0);
	R1 = readl(adc_info->regs + VF610_REG_ADC_R1);
	CFG = readl(adc_info->regs + VF610_REG_ADC_CFG);
	GC = readl(adc_info->regs + VF610_REG_ADC_GC);
	GS = readl(adc_info->regs + VF610_REG_ADC_GS);
	CV = readl(adc_info->regs + VF610_REG_ADC_CV);
	OFS = readl(adc_info->regs + VF610_REG_ADC_OFS);
	CAL = readl(adc_info->regs + VF610_REG_ADC_CAL);

	printk("ADC:%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X\n",
			HC0, HC1, HS, R0, R1, CFG, GC, GS, CV, OFS, CAL );
}                               

static ssize_t show_comparator_window(struct device *dev,
				struct device_attribute *attr, char *buf);

static ssize_t store_comparator_window(struct device *dev,
					struct device_attribute *attr,
					const char *buf, size_t len);

static ssize_t store_hall_enable(struct device *dev,
					struct device_attribute *attr,
					const char *buf, size_t len);

DEVICE_ATTR(comparator_window, S_IRUGO | S_IWUSR, show_comparator_window,
			store_comparator_window);
DEVICE_ATTR(hall_enable, S_IWUSR, NULL ,
			store_hall_enable);

static struct attribute *magwheel_attributes[] = {
	&dev_attr_comparator_window.attr,
	&dev_attr_hall_enable.attr,
	NULL
};

static struct attribute_group magwheel_attribute_group = {
	.attrs		= magwheel_attributes
};

static ssize_t show_comparator_window(struct device *dev,
				struct device_attribute *attr, char *buf)
{
	struct magwheel *mag_info = dev_get_drvdata(dev);

	return sprintf(buf, "%d\n", mag_info->comparator_window);
}

static ssize_t store_comparator_window(struct device *dev,
					struct device_attribute *attr,
					const char *buf, size_t len)
{
	struct magwheel *mag_info = dev_get_drvdata(dev);
	int window;

	sscanf(buf, "%d", &window);

	mag_info->comparator_window = window;

	magwheel_set_window(0, mag_info);
	magwheel_continuous_conversion_start(&mag_info->adc_info);

	return strnlen(buf, len);
}

static ssize_t store_hall_enable(struct device *dev,
					struct device_attribute *attr,
					const char *buf, size_t len)
{
	struct magwheel *mag_info = dev_get_drvdata(dev);
	int enable;

	if (sscanf(buf, "%d", &enable) == 1)
	{
		gpiod_set_value(mag_info->enable_gpio, enable);
	}
	return strnlen(buf, len);
}

static void magwheel_cfg_post_set(struct vf610_adc *adc_info)
{
	int cfg_data = 0;
	int gc_data = 0;

	/* low power set for calibration */
	cfg_data |= VF610_ADC_ADLPC_EN;

	/* enable high speed for calibration */
	cfg_data |= VF610_ADC_ADHSC_EN;

	/* voltage reference */
	cfg_data |= VF610_ADC_REFSEL_VREF;

	/* data overwrite enable */
	cfg_data |= VF610_ADC_OVWREN;

	writel(cfg_data, adc_info->regs + VF610_REG_ADC_CFG);
	writel(gc_data, adc_info->regs + VF610_REG_ADC_GC);
}

static void magwheel_calibration(struct vf610_adc *adc_info)
{
	int adc_gc, hc_cfg;
	int timeout;

	if (adc_info->calibration == true)
		return;

	/* enable calibration interrupt */
	hc_cfg = VF610_ADC_AIEN | VF610_ADC_CONV_DISABLE;
	writel(hc_cfg, adc_info->regs + VF610_REG_ADC_HC0);

	adc_gc = readl(adc_info->regs + VF610_REG_ADC_GC);
	writel(adc_gc | VF610_ADC_CAL, adc_info->regs + VF610_REG_ADC_GC);

	timeout = wait_for_completion_timeout
			(&adc_info->completion, VF610_ADC_TIMEOUT);
	if (timeout == 0)
		dev_err(adc_info->dev, "Timeout for adc calibration\n");

	adc_gc = readl(adc_info->regs + VF610_REG_ADC_GS);
	if (adc_gc & VF610_ADC_CALF)
	{
		dev_err(adc_info->dev, "ADC calibration failed\n");
		adc_info->calibration = false;
	}
	else
	{
		adc_info->calibration = true;
	}
}
static int magwheel_write_raw(struct iio_dev *indio_dev,
		struct iio_chan_spec const *chan,
		int val,
		int val2,
		long mask)
{
	int ret;

	struct magwheel *mag_info = *(struct magwheel**) iio_priv(indio_dev);
	struct vf610_adc *adc_info = &mag_info->adc_info;

	switch (mask)
	{
		case IIO_CHAN_INFO_CALIBSCALE:
			adc_info->scale_int = val;
			adc_info->scale_micro = val2;
			ret = 0;
		break;

		default:
			ret = EINVAL;

	}

	return ret;

}

static int magwheel_read_single_raw(struct iio_dev *indio_dev,
			struct iio_chan_spec const *chan,
			int *val,
			int *val2,
			long mask)
{
	int ret;

	struct magwheel *mag_info = *(struct magwheel**) iio_priv(indio_dev);
	struct vf610_adc *adc_info = &mag_info->adc_info;

	switch (mask) {
	case IIO_CHAN_INFO_RAW:

		mutex_lock(&indio_dev->mlock);
		reinit_completion(&adc_info->completion);

		magwheel_single_conversion_start(adc_info, chan->channel);

		ret = wait_for_completion_interruptible_timeout
				(&adc_info->completion, VF610_ADC_TIMEOUT);

		if (ret == 0) {
			mutex_unlock(&indio_dev->mlock);
			return -ETIMEDOUT;
		}
		if (ret < 0) {
			mutex_unlock(&indio_dev->mlock);
			return ret;
		}

		*val = (adc_info->value * adc_info->scale_int) + ((adc_info->value * adc_info->scale_micro) / 1000000);
		mutex_unlock(&indio_dev->mlock);
		return IIO_VAL_INT;

	case IIO_CHAN_INFO_CALIBSCALE:
		*val = adc_info->scale_int;
		*val2 = adc_info->scale_micro;

		return IIO_VAL_INT_PLUS_MICRO;

	case IIO_CHAN_INFO_SCALE:
		*val = adc_info->vref_uv / 1000;
		*val2 = 12;
		return IIO_VAL_FRACTIONAL_LOG2;

	case IIO_CHAN_INFO_SAMP_FREQ:
		*val = 1941176;
		*val2 = 0;
		return IIO_VAL_INT;

	default:
		return -EINVAL;
	}

}

static void magwheel_single_conversion_start(struct vf610_adc *adc_info, int channel)
{
	int adc_hc;
	int adc_gc;

	/* set up single conversion */
	/* Average enable. No range comparison*/
	adc_gc = VF610_ADC_AVGEN;
	writel(adc_gc, adc_info->regs + VF610_REG_ADC_GC);

	/* Start the single conversion */
	adc_info->channel_index = -1;
	adc_hc = VF610_ADC_ADCHC(channel);

	adc_hc |= VF610_ADC_AIEN;
	writel(adc_hc, adc_info->regs + VF610_REG_ADC_HC0);
}

static void magwheel_continuous_conversion_cfg(struct vf610_adc *adc_info)
{
	int adc_gc;

	/* Turn on continuous conversion */
	adc_gc = readl(adc_info->regs + VF610_REG_ADC_GC);
	/* continuous enable, and trigger on a range enabled */
	adc_gc |= VF610_ADC_ADCON | VF610_ADC_ACFE | VF610_ADC_ACREN
				| VF610_ADC_ACFGT;
	writel(adc_gc, adc_info->regs + VF610_REG_ADC_GC);
}

static void magwheel_continuous_conversion_start(struct vf610_adc *adc_info)
{
	int hc_cfg;

	/* Start the continuous conversion */
	hc_cfg = VF610_ADC_ADCHC(adc_info->channels[adc_info->channel_index]);
	hc_cfg |= VF610_ADC_AIEN;
	writel(hc_cfg, adc_info->regs + VF610_REG_ADC_HC0);
}

static void magwheel_continuous_conversion_init(struct vf610_adc *adc_info)
{
	int adc_cv;

	magwheel_continuous_conversion_cfg(adc_info);

	/*
	 * Pick a comparator range such that the ADC is guaranteed to trigger.
	 * After this, the ISR will set a more strict compareator window,
	 * once it knows the current ADC value
	 */
	adc_cv = MIN_ADC_VAL + ((MAX_ADC_VAL) << VF610_ADC_CV2_SHIFT);
	writel(adc_cv, adc_info->regs + VF610_REG_ADC_CV);

	magwheel_continuous_conversion_start(adc_info);
}

static void magwheel_continuous_conversion_resume(struct vf610_adc *adc_info)
{
	magwheel_continuous_conversion_cfg(adc_info);
	magwheel_continuous_conversion_start(adc_info);
}

static void magwheel_cfg_set(struct vf610_adc *adc_info)
{
	int cfg_data;

	cfg_data = readl(adc_info->regs + VF610_REG_ADC_CFG);

	/* low power configuration */
	cfg_data |= VF610_ADC_ADLPC_EN;

	/* disable high speed */
	cfg_data &= ~VF610_ADC_ADHSC_EN;

	writel(cfg_data, adc_info->regs + VF610_REG_ADC_CFG);
}

static void magwheel_sample_set(struct vf610_adc *adc_info)
{
	int cfg_data, gc_data;

	cfg_data = readl(adc_info->regs + VF610_REG_ADC_CFG);
	gc_data = readl(adc_info->regs + VF610_REG_ADC_GC);

	/* resolution mode */
	cfg_data &= ~VF610_ADC_MODE_MASK;
	cfg_data |= VF610_ADC_MODE_BIT12;

	/* clock select and clock divider */
	cfg_data &= ~(VF610_ADC_CLK_MASK | VF610_ADC_ADCCLK_MASK);
	cfg_data |= VF610_ADC_ADACK_SEL | VF610_ADC_CLK_DIV8;

	/* Use the long sample mode */
	cfg_data |= VF610_ADC_ADLSMP_LONG | VF610_ADC_ADSTS_MASK;

	/* update hardware average selection */
	cfg_data &= ~VF610_ADC_AVGS_MASK;
	gc_data |= VF610_ADC_AVGEN;
	cfg_data |= VF610_ADC_AVGS_32;

	writel(cfg_data, adc_info->regs + VF610_REG_ADC_CFG);
	writel(gc_data, adc_info->regs + VF610_REG_ADC_GC);
}

static void magwheel_hw_init(struct vf610_adc *adc_info, bool is_resume)
{
	/* CFG: Feature set */
	magwheel_cfg_post_set(adc_info);
	magwheel_sample_set(adc_info);

	/* adc calibration */
	magwheel_calibration(adc_info);

	/* CFG: power and speed set */
	magwheel_cfg_set(adc_info);

	if (is_resume)
		magwheel_continuous_conversion_resume(adc_info);
	else
		magwheel_continuous_conversion_init(adc_info);
}

static int magwheel_read_data(struct vf610_adc *adc_info)
{
	int result;

	result = readl(adc_info->regs + VF610_REG_ADC_R0);
	result &= BITS_MASK_12;
	return result;
}

static void magwheel_set_window(int center, struct magwheel *mag_info)
{
	int adc_cv = center + mag_info->comparator_window + ((center - mag_info->comparator_window) << VF610_ADC_CV2_SHIFT);
	writel(adc_cv, mag_info->adc_info.regs + VF610_REG_ADC_CV);
}

static irqreturn_t magwheel_isr(int irq, void *dev_id)
{
	struct magwheel *mag_info = (struct magwheel *)dev_id;
	struct vf610_adc *adc_info = &mag_info->adc_info;
	int coco;
	int value = 0;

	coco = readl(adc_info->regs + VF610_REG_ADC_HS);
	if (coco & VF610_ADC_HS_COCO0) {
		//conversion complete.. This really should happen every time.
		value = magwheel_read_data(adc_info);
		complete(&adc_info->completion);
	}

	if (adc_info->channel_index == 0) {
		/*
		 * Don't interrupt again unless you are X away from
		 * the current ADC value
		 * Note we need to write to HC0 to have an effect on ADC_CV
		 */
		magwheel_set_window(value, mag_info);

		/* switch channels */
		mag_info->buffered_vals1[mag_info->buffered_loc] = value;
		adc_info->channel_index = 1;
	} else if(adc_info->channel_index == 1) {
		mag_info->buffered_vals2[mag_info->buffered_loc] = value;
		/*
		* Only increment the location when switching
		* back to channel 1
		*/
		mag_info->buffered_loc = (mag_info->buffered_loc + 1)
			% BUFFER_LENGTH;
		adc_info->channel_index = 0;
	} else {
		/* must be single read channel. Save this and set up continuous again.*/

		mag_info->adc_info.value = value;
		magwheel_continuous_conversion_cfg(adc_info);
		adc_info->channel_index = 0;

		complete(&adc_info->completion);
	}
	magwheel_continuous_conversion_start(adc_info);

	schedule_delayed_work(
		(struct delayed_work *) &mag_info->readbuffer_work, 2);

	return IRQ_HANDLED;
}

/* Fixed point version of atan2 in math.h. Off by no more than 2 degrees.
 * Using methods described in
 * http://bsvi.ru/uploads/CORDIC--_10EBA/cordic.pdf
 */
static int magwheel_atan2_fp(int y, int x)
{
	int xn;
	/*
	 * 256 = 1 degree, so 11520 = 45 degrees * 256.
	 * Allows us to do this in fixed point style.
	 */
	int sum_angle = 0;
	int i;

	/*
	 * Make sure x and y are big enough to get decent precision;
	 * this only really matters when inputs are small (< 100)
	 */
	x = x << ATAN_HYPO_MULTIPLIER;
	y = y << ATAN_HYPO_MULTIPLIER;
	if (x < 0) {
		x = -x;
		y = -y;
		sum_angle = 180 * 256;
	}
	for (i = 0; i < ATAN_TABLE_SIZE; i++) {
		if (y > 0) {
			xn = x + (y >> i);
			y = y - (x >> i);
			sum_angle += tan_table[i];
		} else if (y < 0) {
			xn =  x - (y >> i);
			y = y + (x >> i);
			sum_angle -= tan_table[i];
		} else {
			break;
		}
		x = xn;
	}
	/* Quadrant III needs to be turned into negative numbers */
	if (sum_angle > (180 * 256))
		return -360 + (sum_angle / 256);
	return sum_angle / 256;
}

/*
 * angle inputs are from -180 to 180
 * Returns the amount of degrees to change, positive or negative
 *  (i.e. new_angle is -10 degrees in front of last_angle)
 *
 * There are two possible answers, but we guess that the one with
 * the least change is right
 */
static int get_angle_change(int last_angle, int new_angle)
{
	/* The angle went forward this much */
	int change_needed_forward;
	int change_needed_backward;
	change_needed_forward = (new_angle + 360) - last_angle;
	if (change_needed_forward >= 360)
		change_needed_forward -= 360;
	/* Or backwards this much */
	change_needed_backward = (last_angle + 360) - new_angle;
	if (change_needed_backward >= 360)
		change_needed_backward -= 360;

	/* Whichever is the least change is the answer */
	if (change_needed_forward < change_needed_backward)
		return change_needed_forward;
	return -change_needed_backward;
}

static void wait_handler(struct work_struct *work)
{
	int i;
	int start, end;
	int current_angle;
	int angle_change;
	int total_angle_change = 0;
	/* Cast so we can get access to mag_info */
	struct magwheel_work *magwheel_work = (struct magwheel_work *) work;
	struct magwheel *mag_info = magwheel_work->mag_info;
	struct vf610_adc *adc_info = &mag_info->adc_info;
	struct input_dev *input = adc_info->input_dev;


	/* get min/max */
	start = mag_info->buffered_loc_last;
	/* don't need to lock here b/c we are just reading */
	end = mag_info->buffered_loc;
	for (i = start; i != end; i = (i + 1) % BUFFER_LENGTH) {
		/* Also calculate what the new angle should be */
		current_angle = magwheel_atan2_fp(
			mag_info->buffered_vals2[i]
				- adc_info->channel_midpoints[1],
			mag_info->buffered_vals1[i]
				- adc_info->channel_midpoints[0]);
		angle_change =
			get_angle_change(mag_info->last_angle, current_angle);
		total_angle_change += angle_change;
		mag_info->last_angle = current_angle;
	}
	mag_info->buffered_loc_last = end;

	pm_wakeup_event(adc_info->dev, 0);

	input_report_rel(input, REL_DIAL, total_angle_change);
	input_sync(input);
}


static const struct of_device_id magwheel_match[] = {
	{ .compatible = "nestlabs,vf610-adc-magwheel", },
	{ /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, magwheel_match);

static const struct iio_info magwheel_iio_info = {
	.driver_module = THIS_MODULE,
	.read_raw = &magwheel_read_single_raw,
	.write_raw = &magwheel_write_raw,
};

static int magwheel_probe(struct platform_device *pdev)
{
	struct vf610_adc *adc_info;
	struct magwheel *mag_info;
	struct resource *mem;
	int err;
	struct input_dev *input;
	int size = sizeof(struct magwheel);

	mag_info = devm_kzalloc(&pdev->dev, size, GFP_KERNEL);
	if (!mag_info)
		return -ENOMEM;

	/* Turn on the hall sensor */
	mag_info->enable_gpio = devm_gpiod_get(&pdev->dev, "hall-sensor-enable");
	if (!IS_ERR(mag_info->enable_gpio)) {
		gpiod_direction_output(mag_info->enable_gpio, 1);
		gpiod_set_value(mag_info->enable_gpio, 1);

		dev_info(&pdev->dev, "register hall-sensor-enable-gpio\n");
		/* Wait to charge up */
		usleep_range(ENABLE_DELAY_MIN_US, ENABLE_DELAY_MAX_US);
	} else {
		dev_info(&pdev->dev, "fail to register hall-sensor-enable-gpio %d\n", PTR_ERR(mag_info->enable_gpio));
	        mag_info->enable_gpio = NULL;
	}

	mag_info->comparator_window = COMPARATOR_WINDOW_INIT;

	mag_info->indio_dev = devm_iio_device_alloc(&pdev->dev, sizeof(struct magwheel*));
	if (!mag_info->indio_dev) {
		dev_err(&pdev->dev, "Failed allocating iio device\n");
		return -ENOMEM;
	}

	*(struct magwheel**) iio_priv(mag_info->indio_dev) = mag_info;

	mag_info->indio_dev->name = dev_name(&pdev->dev);
	mag_info->indio_dev->dev.parent = &pdev->dev;
	mag_info->indio_dev->dev.of_node = pdev->dev.of_node;
	mag_info->indio_dev->info = &magwheel_iio_info;
	mag_info->indio_dev->modes = INDIO_DIRECT_MODE;
	mag_info->indio_dev->channels = vf610_adc_iio_channels;
	mag_info->indio_dev->num_channels = ARRAY_SIZE(vf610_adc_iio_channels);

	err = iio_device_register(mag_info->indio_dev);

	adc_info = &mag_info->adc_info;
	adc_info->scale_int = 1;
	adc_info->scale_micro = 0;


	if (of_property_read_u32_array(pdev->dev.of_node,
		"nestlabs,adc-channels-used", adc_info->channels, 2)) {
		dev_err(&pdev->dev,
			"adc-channels-used property in the DT needs to be a 2 element u32 array.\n");
		return -EINVAL;
	}

	if (of_property_read_u32_array(pdev->dev.of_node,
		"nestlabs,adc-channel-midpoints",
		adc_info->channel_midpoints, 2)) {
		dev_err(&pdev->dev,
			"adc-channel-midpoints property in the DT needs to be a 2 element u32 array.\n");
		return -EINVAL;
	}

	INIT_DELAYED_WORK((struct delayed_work *) &mag_info->readbuffer_work,
		wait_handler);

	input = input_allocate_device();
	if (!mag_info || !input) {
		dev_err(&pdev->dev, "Not enough memory for this driver!\n");
		return -ENOMEM;
	}
	adc_info->input_dev = input;
	adc_info->channel_index = 0;

	input->name = pdev->name;
	input->id.bustype = BUS_HOST;
	input->dev.parent = &pdev->dev;
	input_set_capability(input, EV_REL, REL_DIAL);

	/* Yes, mag_info has a readbuffer which points back to mag_info.
	 * That's because the work handler only gets readbuffer_work,
	 * and we want a pointer to mag_info
	 */
	mag_info->readbuffer_work.mag_info = mag_info;
	adc_info->dev = &pdev->dev;

	device_init_wakeup(&pdev->dev, 1);

	mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
	if (mem == NULL) {
		dev_err(&pdev->dev, "found no memory resource\n");
		return -ENXIO;
	}

	adc_info->regs = devm_ioremap_resource(&pdev->dev, mem);
	if (IS_ERR(adc_info->regs))
		return PTR_ERR(adc_info->regs);

	adc_info->irq = platform_get_irq(pdev, 0);
	if (adc_info->irq <= 0) {
		dev_err(&pdev->dev, "no irq resource?\n");
		return -EINVAL;
	}

	err = devm_request_irq(adc_info->dev, adc_info->irq,
				magwheel_isr, 0,
				dev_name(&pdev->dev), adc_info);
	if (err < 0) {
		dev_err(&pdev->dev,
			"failed requesting irq, irq = %d\n", adc_info->irq);
		return err;
	}

	adc_info->clk = devm_clk_get(&pdev->dev, "adc");
	if (IS_ERR(adc_info->clk)) {
		dev_err(&pdev->dev, "failed getting clock, err = %ld\n",
						PTR_ERR(adc_info->clk));
		err = PTR_ERR(adc_info->clk);
		return err;
	}

	adc_info->vref = devm_regulator_get(&pdev->dev, "vref");
	if (IS_ERR(adc_info->vref))
		return PTR_ERR(adc_info->vref);

	err = regulator_enable(adc_info->vref);
	if (err)
		return err;

	adc_info->vref_uv = regulator_get_voltage(adc_info->vref);

	platform_set_drvdata(pdev, adc_info);

	init_completion(&adc_info->completion);

	magwheel_hw_init(adc_info, false);

	err = clk_prepare_enable(adc_info->clk);
	if (err) {
		dev_err(&pdev->dev,
			"Could not prepare or enable the clock.\n");
		goto error_adc_clk_enable;
	}

	err = input_register_device(input);
	if (err) {
		dev_err(&pdev->dev, "poll not working\n");
		goto error_input_register;
	}

	err = sysfs_create_group(&pdev->dev.kobj, &magwheel_attribute_group);
	if (err < 0) {
		dev_err(&pdev->dev, "failed to create sysfs attributes\n");
		goto error_sysfs_register;
	}

	return 0;

error_sysfs_register:
	input_unregister_device(adc_info->input_dev);

error_input_register:
	clk_disable_unprepare(adc_info->clk);

error_adc_clk_enable:
	platform_set_drvdata(pdev, NULL);
	regulator_disable(adc_info->vref);

	return err;
}

static int magwheel_remove(struct platform_device *pdev)
{
	struct magwheel *mag_info = platform_get_drvdata(pdev);
	struct vf610_adc *adc_info = &mag_info->adc_info;

	device_init_wakeup(adc_info->dev, 0);

	sysfs_remove_group(&pdev->dev.kobj, &magwheel_attribute_group);
	input_unregister_device(adc_info->input_dev);
	platform_set_drvdata(pdev, NULL);
	clk_disable_unprepare(adc_info->clk);
	regulator_disable(adc_info->vref);

	return 0;
}

#ifdef CONFIG_PM_SLEEP
static int magwheel_suspend(struct device *dev)
{
	struct magwheel *mag_info = dev_get_drvdata(dev);
	struct vf610_adc *adc_info = &mag_info->adc_info;
	int hc_cfg;

	/* ADC controller enters to stop mode */
	hc_cfg = readl(adc_info->regs + VF610_REG_ADC_HC0);
	hc_cfg |= VF610_ADC_CONV_DISABLE;
	writel(hc_cfg, adc_info->regs + VF610_REG_ADC_HC0);

	clk_disable_unprepare(adc_info->clk);
	regulator_disable(adc_info->vref);

	/* Turn off the hall sensor */
	gpiod_set_value(mag_info->enable_gpio, 0);

	return 0;
}

static int magwheel_resume(struct device *dev)
{
	struct magwheel *mag_info = dev_get_drvdata(dev);
	struct vf610_adc *adc_info = &mag_info->adc_info;
	int ret;

	/* Turn on the hall sensor */
	gpiod_set_value(mag_info->enable_gpio, 1);
	if (mag_info->enable_gpio) {
		/* Wait to charge up */
		usleep_range(ENABLE_DELAY_MIN_US, ENABLE_DELAY_MAX_US);
	}

	ret = clk_prepare_enable(adc_info->clk);
	ret = regulator_enable(adc_info->vref);
	if (ret)
		return ret;

	magwheel_hw_init(adc_info, true);

	return 0;
}
#endif

static SIMPLE_DEV_PM_OPS(magwheel_pm_ops,
			magwheel_suspend,
			magwheel_resume);

static struct platform_driver magwheel_driver = {
	.probe          = magwheel_probe,
	.remove         = magwheel_remove,
	.driver         = {
		.name   = DRIVER_NAME,
		.owner  = THIS_MODULE,
		.of_match_table = magwheel_match,
		.pm     = &magwheel_pm_ops,
	},
};

module_platform_driver(magwheel_driver);

MODULE_AUTHOR("Chase Lambert <clambert@nestlabs.com>");
MODULE_DESCRIPTION("Nest Labs Magwheel Driver");
MODULE_LICENSE("GPL v2");