/*
 * ADS7846 based touchscreen and sensor driver
 *
 * Copyright (c) 2005 David Brownell
 * Copyright (c) 2006 Nokia Corporation
 * Various changes: Imre Deak <imre.deak@nokia.com>
 *
 * Using code from:
 *  - corgi_ts.c
 *      Copyright (C) 2004-2005 Richard Purdie
 *  - omap_ts.[hc], ads7846.h, ts_osk.c
 *      Copyright (C) 2002 MontaVista Software
 *      Copyright (C) 2004 Texas Instruments
 *      Copyright (C) 2005 Dirk Behme
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2 as
 *  published by the Free Software Foundation.
 */
#include <linux/types.h>
#include <linux/hwmon.h>
#include <linux/init.h>
#include <linux/err.h>
#include <linux/sched.h>
#include <linux/delay.h>
#include <linux/input.h>
#include <linux/interrupt.h>
#include <linux/slab.h>
#include <linux/pm.h>
#include <linux/of.h>
#include <linux/of_gpio.h>
#include <linux/of_device.h>
#include <linux/gpio.h>
#include <linux/spi/spi.h>
#include <linux/spi/ads7846.h>
#include <linux/regulator/consumer.h>
#include <linux/module.h>
#include <asm/irq.h>

/*
 * This code has been heavily tested on a Nokia 770, and lightly
 * tested on other ads7846 devices (OSK/Mistral, Lubbock, Spitz).
 * TSC2046 is just newer ads7846 silicon.
 * Support for ads7843 tested on Atmel at91sam926x-EK.
 * Support for ads7845 has only been stubbed in.
 * Support for Analog Devices AD7873 and AD7843 tested.
 *
 * IRQ handling needs a workaround because of a shortcoming in handling
 * edge triggered IRQs on some platforms like the OMAP1/2. These
 * platforms don't handle the ARM lazy IRQ disabling properly, thus we
 * have to maintain our own SW IRQ disabled status. This should be
 * removed as soon as the affected platform's IRQ handling is fixed.
 *
 * App note sbaa036 talks in more detail about accurate sampling...
 * that ought to help in situations like LCDs inducing noise (which
 * can also be helped by using synch signals) and more generally.
 * This driver tries to utilize the measures described in the app
 * note. The strength of filtering can be set in the board-* specific
 * files.
 */

#define TS_POLL_DELAY   1       /* ms delay before the first sample */
#define TS_POLL_PERIOD  5       /* ms delay between samples */

/* this driver doesn't aim at the peak continuous sample rate */
#define SAMPLE_BITS     (8 /*cmd*/ + 16 /*sample*/ + 2 /* before, after */)

struct ts_event {
        /*
         * For portability, we can't read 12 bit values using SPI (which
         * would make the controller deliver them as native byte order u16
         * with msbs zeroed).  Instead, we read them as two 8-bit values,
         * *** WHICH NEED BYTESWAPPING *** and range adjustment.
         */
        u16     x;
        u16     y;
        u16     z1, z2;
        bool    ignore;
        u8      x_buf[3];
        u8      y_buf[3];
};

/*
 * We allocate this separately to avoid cache line sharing issues when
 * driver is used with DMA-based SPI controllers (like atmel_spi) on
 * systems where main memory is not DMA-coherent (most non-x86 boards).
 */
struct ads7846_packet {
        u8                      read_x, read_y, read_z1, read_z2, pwrdown;
        u16                     dummy;          /* for the pwrdown read */
        struct ts_event         tc;
        /* for ads7845 with mpc5121 psc spi we use 3-byte buffers */
        u8                      read_x_cmd[3], read_y_cmd[3], pwrdown_cmd[3];
};

struct ads7846 {
        struct input_dev        *input;
        char                    phys[32];
        char                    name[32];

        struct spi_device       *spi;
        struct regulator        *reg;

#if defined(CONFIG_HWMON) || defined(CONFIG_HWMON_MODULE)
        struct attribute_group  *attr_group;
        struct device           *hwmon;
#endif

        u16                     model;
        u16                     vref_mv;
        u16                     vref_delay_usecs;
        u16                     x_plate_ohms;
        u16                     pressure_max;

        bool                    swap_xy;
        bool                    use_internal;

        struct ads7846_packet   *packet;

        struct spi_transfer     xfer[18];
        struct spi_message      msg[5];
        int                     msg_count;
        wait_queue_head_t       wait;

        bool                    pendown;

        int                     read_cnt;
        int                     read_rep;
        int                     last_read;

        u16                     debounce_max;
        u16                     debounce_tol;
        u16                     debounce_rep;

        u16                     penirq_recheck_delay_usecs;

        struct mutex            lock;
        bool                    stopped;        /* P: lock */
        bool                    disabled;       /* P: lock */
        bool                    suspended;      /* P: lock */

        int                     (*filter)(void *data, int data_idx, int *val);
        void                    *filter_data;
        void                    (*filter_cleanup)(void *data);
        int                     (*get_pendown_state)(void);
        int                     gpio_pendown;

        void                    (*wait_for_sync)(void);
};

/* leave chip selected when we're done, for quicker re-select? */
#if     0
#define CS_CHANGE(xfer) ((xfer).cs_change = 1)
#else
#define CS_CHANGE(xfer) ((xfer).cs_change = 0)
#endif

/*--------------------------------------------------------------------------*/

/* The ADS7846 has touchscreen and other sensors.
 * Earlier ads784x chips are somewhat compatible.
 */
#define ADS_START               (1 << 7)
#define ADS_A2A1A0_d_y          (1 << 4)        /* differential */
#define ADS_A2A1A0_d_z1         (3 << 4)        /* differential */
#define ADS_A2A1A0_d_z2         (4 << 4)        /* differential */
#define ADS_A2A1A0_d_x          (5 << 4)        /* differential */
#define ADS_A2A1A0_temp0        (0 << 4)        /* non-differential */
#define ADS_A2A1A0_vbatt        (2 << 4)        /* non-differential */
#define ADS_A2A1A0_vaux         (6 << 4)        /* non-differential */
#define ADS_A2A1A0_temp1        (7 << 4)        /* non-differential */
#define ADS_8_BIT               (1 << 3)
#define ADS_12_BIT              (0 << 3)
#define ADS_SER                 (1 << 2)        /* non-differential */
#define ADS_DFR                 (0 << 2)        /* differential */
#define ADS_PD10_PDOWN          (0 << 0)        /* low power mode + penirq */
#define ADS_PD10_ADC_ON         (1 << 0)        /* ADC on */
#define ADS_PD10_REF_ON         (2 << 0)        /* vREF on + penirq */
#define ADS_PD10_ALL_ON         (3 << 0)        /* ADC + vREF on */

#define MAX_12BIT       ((1<<12)-1)

/* leave ADC powered up (disables penirq) between differential samples */
#define READ_12BIT_DFR(x, adc, vref) (ADS_START | ADS_A2A1A0_d_ ## x \
        | ADS_12_BIT | ADS_DFR | \
        (adc ? ADS_PD10_ADC_ON : 0) | (vref ? ADS_PD10_REF_ON : 0))

#define READ_Y(vref)    (READ_12BIT_DFR(y,  1, vref))
#define READ_Z1(vref)   (READ_12BIT_DFR(z1, 1, vref))
#define READ_Z2(vref)   (READ_12BIT_DFR(z2, 1, vref))

#define READ_X(vref)    (READ_12BIT_DFR(x,  1, vref))
#define PWRDOWN         (READ_12BIT_DFR(y,  0, 0))      /* LAST */

/* single-ended samples need to first power up reference voltage;
 * we leave both ADC and VREF powered
 */
#define READ_12BIT_SER(x) (ADS_START | ADS_A2A1A0_ ## x \
        | ADS_12_BIT | ADS_SER)

#define REF_ON  (READ_12BIT_DFR(x, 1, 1))
#define REF_OFF (READ_12BIT_DFR(y, 0, 0))

/* Must be called with ts->lock held */
static void ads7846_stop(struct ads7846 *ts)
{
        if (!ts->disabled && !ts->suspended) {
                /* Signal IRQ thread to stop polling and disable the handler. */
                ts->stopped = true;
                mb();
                wake_up(&ts->wait);
                disable_irq(ts->spi->irq);
        }
}

/* Must be called with ts->lock held */
static void ads7846_restart(struct ads7846 *ts)
{
        if (!ts->disabled && !ts->suspended) {
                /* Tell IRQ thread that it may poll the device. */
                ts->stopped = false;
                mb();
                enable_irq(ts->spi->irq);
        }
}

/* Must be called with ts->lock held */
static void __ads7846_disable(struct ads7846 *ts)
{
        ads7846_stop(ts);
        regulator_disable(ts->reg);

        /*
         * We know the chip's in low power mode since we always
         * leave it that way after every request
         */
}

/* Must be called with ts->lock held */
static void __ads7846_enable(struct ads7846 *ts)
{
        int error;

        error = regulator_enable(ts->reg);
        if (error != 0)
                dev_err(&ts->spi->dev, "Failed to enable supply: %d\n", error);

        ads7846_restart(ts);
}

static void ads7846_disable(struct ads7846 *ts)
{
        mutex_lock(&ts->lock);

        if (!ts->disabled) {

                if  (!ts->suspended)
                        __ads7846_disable(ts);

                ts->disabled = true;
        }

        mutex_unlock(&ts->lock);
}

static void ads7846_enable(struct ads7846 *ts)
{
        mutex_lock(&ts->lock);

        if (ts->disabled) {

                ts->disabled = false;

                if (!ts->suspended)
                        __ads7846_enable(ts);
        }

        mutex_unlock(&ts->lock);
}

/*--------------------------------------------------------------------------*/

/*
 * Non-touchscreen sensors only use single-ended conversions.
 * The range is GND..vREF. The ads7843 and ads7835 must use external vREF;
 * ads7846 lets that pin be unconnected, to use internal vREF.
 */

struct ser_req {
        u8                      ref_on;
        u8                      command;
        u8                      ref_off;
        u16                     scratch;
        struct spi_message      msg;
        struct spi_transfer     xfer[6];
        /*
         * DMA (thus cache coherency maintenance) requires the
         * transfer buffers to live in their own cache lines.
         */
        __be16 sample ____cacheline_aligned;
};

struct ads7845_ser_req {
        u8                      command[3];
        struct spi_message      msg;
        struct spi_transfer     xfer[2];
        /*
         * DMA (thus cache coherency maintenance) requires the
         * transfer buffers to live in their own cache lines.
         */
        u8 sample[3] ____cacheline_aligned;
};

static int ads7846_read12_ser(struct device *dev, unsigned command)
{
        struct spi_device *spi = to_spi_device(dev);
        struct ads7846 *ts = dev_get_drvdata(dev);
        struct ser_req *req;
        int status;

        req = kzalloc(sizeof *req, GFP_KERNEL);
        if (!req)
                return -ENOMEM;

        spi_message_init(&req->msg);

        /* maybe turn on internal vREF, and let it settle */
        if (ts->use_internal) {
                req->ref_on = REF_ON;
                req->xfer[0].tx_buf = &req->ref_on;
                req->xfer[0].len = 1;
                spi_message_add_tail(&req->xfer[0], &req->msg);

                req->xfer[1].rx_buf = &req->scratch;
                req->xfer[1].len = 2;

                /* for 1uF, settle for 800 usec; no cap, 100 usec.  */
                req->xfer[1].delay_usecs = ts->vref_delay_usecs;
                spi_message_add_tail(&req->xfer[1], &req->msg);

                /* Enable reference voltage */
                command |= ADS_PD10_REF_ON;
        }

        /* Enable ADC in every case */
        command |= ADS_PD10_ADC_ON;

        /* take sample */
        req->command = (u8) command;
        req->xfer[2].tx_buf = &req->command;
        req->xfer[2].len = 1;
        spi_message_add_tail(&req->xfer[2], &req->msg);

        req->xfer[3].rx_buf = &req->sample;
        req->xfer[3].len = 2;
        spi_message_add_tail(&req->xfer[3], &req->msg);

        /* REVISIT:  take a few more samples, and compare ... */

        /* converter in low power mode & enable PENIRQ */
        req->ref_off = PWRDOWN;
        req->xfer[4].tx_buf = &req->ref_off;
        req->xfer[4].len = 1;
        spi_message_add_tail(&req->xfer[4], &req->msg);

        req->xfer[5].rx_buf = &req->scratch;
        req->xfer[5].len = 2;
        CS_CHANGE(req->xfer[5]);
        spi_message_add_tail(&req->xfer[5], &req->msg);

        mutex_lock(&ts->lock);
        ads7846_stop(ts);
        status = spi_sync(spi, &req->msg);
        ads7846_restart(ts);
        mutex_unlock(&ts->lock);

        if (status == 0) {
                /* on-wire is a must-ignore bit, a BE12 value, then padding */
                status = be16_to_cpu(req->sample);
                status = status >> 3;
                status &= 0x0fff;
        }

        kfree(req);
        return status;
}

static int ads7845_read12_ser(struct device *dev, unsigned command)
{
        struct spi_device *spi = to_spi_device(dev);
        struct ads7846 *ts = dev_get_drvdata(dev);
        struct ads7845_ser_req *req;
        int status;

        req = kzalloc(sizeof *req, GFP_KERNEL);
        if (!req)
                return -ENOMEM;

        spi_message_init(&req->msg);

        req->command[0] = (u8) command;
        req->xfer[0].tx_buf = req->command;
        req->xfer[0].rx_buf = req->sample;
        req->xfer[0].len = 3;
        spi_message_add_tail(&req->xfer[0], &req->msg);

        mutex_lock(&ts->lock);
        ads7846_stop(ts);
        status = spi_sync(spi, &req->msg);
        ads7846_restart(ts);
        mutex_unlock(&ts->lock);

        if (status == 0) {
                /* BE12 value, then padding */
                status = be16_to_cpu(*((u16 *)&req->sample[1]));
                status = status >> 3;
                status &= 0x0fff;
        }

        kfree(req);
        return status;
}

#if defined(CONFIG_HWMON) || defined(CONFIG_HWMON_MODULE)

#define SHOW(name, var, adjust) static ssize_t \
name ## _show(struct device *dev, struct device_attribute *attr, char *buf) \
{ \
        struct ads7846 *ts = dev_get_drvdata(dev); \
        ssize_t v = ads7846_read12_ser(dev, \
                        READ_12BIT_SER(var)); \
        if (v < 0) \
                return v; \
        return sprintf(buf, "%u\n", adjust(ts, v)); \
} \
static DEVICE_ATTR(name, S_IRUGO, name ## _show, NULL);


/* Sysfs conventions report temperatures in millidegrees Celsius.
 * ADS7846 could use the low-accuracy two-sample scheme, but can't do the high
 * accuracy scheme without calibration data.  For now we won't try either;
 * userspace sees raw sensor values, and must scale/calibrate appropriately.
 */
static inline unsigned null_adjust(struct ads7846 *ts, ssize_t v)
{
        return v;
}

SHOW(temp0, temp0, null_adjust)         /* temp1_input */
SHOW(temp1, temp1, null_adjust)         /* temp2_input */


/* sysfs conventions report voltages in millivolts.  We can convert voltages
 * if we know vREF.  userspace may need to scale vAUX to match the board's
 * external resistors; we assume that vBATT only uses the internal ones.
 */
static inline unsigned vaux_adjust(struct ads7846 *ts, ssize_t v)
{
        unsigned retval = v;

        /* external resistors may scale vAUX into 0..vREF */
        retval *= ts->vref_mv;
        retval = retval >> 12;

        return retval;
}

static inline unsigned vbatt_adjust(struct ads7846 *ts, ssize_t v)
{
        unsigned retval = vaux_adjust(ts, v);

        /* ads7846 has a resistor ladder to scale this signal down */
        if (ts->model == 7846)
                retval *= 4;

        return retval;
}

SHOW(in0_input, vaux, vaux_adjust)
SHOW(in1_input, vbatt, vbatt_adjust)

static struct attribute *ads7846_attributes[] = {
        &dev_attr_temp0.attr,
        &dev_attr_temp1.attr,
        &dev_attr_in0_input.attr,
        &dev_attr_in1_input.attr,
        NULL,
};

static struct attribute_group ads7846_attr_group = {
        .attrs = ads7846_attributes,
};

static struct attribute *ads7843_attributes[] = {
        &dev_attr_in0_input.attr,
        &dev_attr_in1_input.attr,
        NULL,
};

static struct attribute_group ads7843_attr_group = {
        .attrs = ads7843_attributes,
};

static struct attribute *ads7845_attributes[] = {
        &dev_attr_in0_input.attr,
        NULL,
};

static struct attribute_group ads7845_attr_group = {
        .attrs = ads7845_attributes,
};

static int ads784x_hwmon_register(struct spi_device *spi, struct ads7846 *ts)
{
        struct device *hwmon;
        int err;

        /* hwmon sensors need a reference voltage */
        switch (ts->model) {
        case 7846:
                if (!ts->vref_mv) {
                        dev_dbg(&spi->dev, "assuming 2.5V internal vREF\n");
                        ts->vref_mv = 2500;
                        ts->use_internal = true;
                }
                break;
        case 7845:
        case 7843:
                if (!ts->vref_mv) {
                        dev_warn(&spi->dev,
                                "external vREF for ADS%d not specified\n",
                                ts->model);
                        return 0;
                }
                break;
        }

        /* different chips have different sensor groups */
        switch (ts->model) {
        case 7846:
                ts->attr_group = &ads7846_attr_group;
                break;
        case 7845:
                ts->attr_group = &ads7845_attr_group;
                break;
        case 7843:
                ts->attr_group = &ads7843_attr_group;
                break;
        default:
                dev_dbg(&spi->dev, "ADS%d not recognized\n", ts->model);
                return 0;
        }

        err = sysfs_create_group(&spi->dev.kobj, ts->attr_group);
        if (err)
                return err;

        hwmon = hwmon_device_register(&spi->dev);
        if (IS_ERR(hwmon)) {
                sysfs_remove_group(&spi->dev.kobj, ts->attr_group);
                return PTR_ERR(hwmon);
        }

        ts->hwmon = hwmon;
        return 0;
}

static void ads784x_hwmon_unregister(struct spi_device *spi,
                                     struct ads7846 *ts)
{
        if (ts->hwmon) {
                sysfs_remove_group(&spi->dev.kobj, ts->attr_group);
                hwmon_device_unregister(ts->hwmon);
        }
}

#else
static inline int ads784x_hwmon_register(struct spi_device *spi,
                                         struct ads7846 *ts)
{
        return 0;
}

static inline void ads784x_hwmon_unregister(struct spi_device *spi,
                                            struct ads7846 *ts)
{
}
#endif

static ssize_t ads7846_pen_down_show(struct device *dev,
                                     struct device_attribute *attr, char *buf)
{
        struct ads7846 *ts = dev_get_drvdata(dev);

        return sprintf(buf, "%u\n", ts->pendown);
}

static DEVICE_ATTR(pen_down, S_IRUGO, ads7846_pen_down_show, NULL);

static ssize_t ads7846_disable_show(struct device *dev,
                                     struct device_attribute *attr, char *buf)
{
        struct ads7846 *ts = dev_get_drvdata(dev);

        return sprintf(buf, "%u\n", ts->disabled);
}

static ssize_t ads7846_disable_store(struct device *dev,
                                     struct device_attribute *attr,
                                     const char *buf, size_t count)
{
        struct ads7846 *ts = dev_get_drvdata(dev);
        unsigned int i;
        int err;

        err = kstrtouint(buf, 10, &i);
        if (err)
                return err;

        if (i)
                ads7846_disable(ts);
        else
                ads7846_enable(ts);

        return count;
}

static DEVICE_ATTR(disable, 0664, ads7846_disable_show, ads7846_disable_store);

static struct attribute *ads784x_attributes[] = {
        &dev_attr_pen_down.attr,
        &dev_attr_disable.attr,
        NULL,
};

static struct attribute_group ads784x_attr_group = {
        .attrs = ads784x_attributes,
};

/*--------------------------------------------------------------------------*/

static int get_pendown_state(struct ads7846 *ts)
{
        if (ts->get_pendown_state)
                return ts->get_pendown_state();

        return !gpio_get_value(ts->gpio_pendown);
}

static void null_wait_for_sync(void)
{
}

static int ads7846_debounce_filter(void *ads, int data_idx, int *val)
{
        struct ads7846 *ts = ads;

        if (!ts->read_cnt || (abs(ts->last_read - *val) > ts->debounce_tol)) {
                /* Start over collecting consistent readings. */
                ts->read_rep = 0;
                /*
                 * Repeat it, if this was the first read or the read
                 * wasn't consistent enough.
                 */
                if (ts->read_cnt < ts->debounce_max) {
                        ts->last_read = *val;
                        ts->read_cnt++;
                        return ADS7846_FILTER_REPEAT;
                } else {
                        /*
                         * Maximum number of debouncing reached and still
                         * not enough number of consistent readings. Abort
                         * the whole sample, repeat it in the next sampling
                         * period.
                         */
                        ts->read_cnt = 0;
                        return ADS7846_FILTER_IGNORE;
                }
        } else {
                if (++ts->read_rep > ts->debounce_rep) {
                        /*
                         * Got a good reading for this coordinate,
                         * go for the next one.
                         */
                        ts->read_cnt = 0;
                        ts->read_rep = 0;
                        return ADS7846_FILTER_OK;
                } else {
                        /* Read more values that are consistent. */
                        ts->read_cnt++;
                        return ADS7846_FILTER_REPEAT;
                }
        }
}

static int ads7846_no_filter(void *ads, int data_idx, int *val)
{
        return ADS7846_FILTER_OK;
}

static int ads7846_get_value(struct ads7846 *ts, struct spi_message *m)
{
        struct spi_transfer *t =
                list_entry(m->transfers.prev, struct spi_transfer, transfer_list);

        if (ts->model == 7845) {
                return be16_to_cpup((__be16 *)&(((char*)t->rx_buf)[1])) >> 3;
        } else {
                /*
                 * adjust:  on-wire is a must-ignore bit, a BE12 value, then
                 * padding; built from two 8 bit values written msb-first.
                 */
                return be16_to_cpup((__be16 *)t->rx_buf) >> 3;
        }
}

static void ads7846_update_value(struct spi_message *m, int val)
{
        struct spi_transfer *t =
                list_entry(m->transfers.prev, struct spi_transfer, transfer_list);

        *(u16 *)t->rx_buf = val;
}

static void ads7846_read_state(struct ads7846 *ts)
{
        struct ads7846_packet *packet = ts->packet;
        struct spi_message *m;
        int msg_idx = 0;
        int val;
        int action;
        int error;

        while (msg_idx < ts->msg_count) {

                ts->wait_for_sync();

                m = &ts->msg[msg_idx];
                error = spi_sync(ts->spi, m);
                if (error) {
                        dev_err(&ts->spi->dev, "spi_async --> %d\n", error);
                        packet->tc.ignore = true;
                        return;
                }

                /*
                 * Last message is power down request, no need to convert
                 * or filter the value.
                 */
                if (msg_idx < ts->msg_count - 1) {

                        val = ads7846_get_value(ts, m);

                        action = ts->filter(ts->filter_data, msg_idx, &val);
                        switch (action) {
                        case ADS7846_FILTER_REPEAT:
                                continue;

                        case ADS7846_FILTER_IGNORE:
                                packet->tc.ignore = true;
                                msg_idx = ts->msg_count - 1;
                                continue;

                        case ADS7846_FILTER_OK:
                                ads7846_update_value(m, val);
                                packet->tc.ignore = false;
                                msg_idx++;
                                break;

                        default:
                                BUG();
                        }
                } else {
                        msg_idx++;
                }
        }
}

static void ads7846_report_state(struct ads7846 *ts)
{
        struct ads7846_packet *packet = ts->packet;
        unsigned int Rt;
        u16 x, y, z1, z2;

        /*
         * ads7846_get_value() does in-place conversion (including byte swap)
         * from on-the-wire format as part of debouncing to get stable
         * readings.
         */
        if (ts->model == 7845) {
                x = *(u16 *)packet->tc.x_buf;
                y = *(u16 *)packet->tc.y_buf;
                z1 = 0;
                z2 = 0;
        } else {
                x = packet->tc.x;
                y = packet->tc.y;
                z1 = packet->tc.z1;
                z2 = packet->tc.z2;
        }

        /* range filtering */
        if (x == MAX_12BIT)
                x = 0;

        if (ts->model == 7843) {
                Rt = ts->pressure_max / 2;
        } else if (ts->model == 7845) {
                if (get_pendown_state(ts))
                        Rt = ts->pressure_max / 2;
                else
                        Rt = 0;
                dev_vdbg(&ts->spi->dev, "x/y: %d/%d, PD %d\n", x, y, Rt);
        } else if (likely(x && z1)) {
                /* compute touch pressure resistance using equation #2 */
                Rt = z2;
                Rt -= z1;
                Rt *= x;
                Rt *= ts->x_plate_ohms;
                Rt /= z1;
                Rt = (Rt + 2047) >> 12;
        } else {
                Rt = 0;
        }

        /*
         * Sample found inconsistent by debouncing or pressure is beyond
         * the maximum. Don't report it to user space, repeat at least
         * once more the measurement
         */
        if (packet->tc.ignore || Rt > ts->pressure_max) {
                dev_vdbg(&ts->spi->dev, "ignored %d pressure %d\n",
                         packet->tc.ignore, Rt);
                return;
        }

        /*
         * Maybe check the pendown state before reporting. This discards
         * false readings when the pen is lifted.
         */
        if (ts->penirq_recheck_delay_usecs) {
                udelay(ts->penirq_recheck_delay_usecs);
                if (!get_pendown_state(ts))
                        Rt = 0;
        }

        /*
         * NOTE: We can't rely on the pressure to determine the pen down
         * state, even this controller has a pressure sensor. The pressure
         * value can fluctuate for quite a while after lifting the pen and
         * in some cases may not even settle at the expected value.
         *
         * The only safe way to check for the pen up condition is in the
         * timer by reading the pen signal state (it's a GPIO _and_ IRQ).
         */
        if (Rt) {
                struct input_dev *input = ts->input;

                if (ts->swap_xy)
                        swap(x, y);

                if (!ts->pendown) {
                        input_report_key(input, BTN_TOUCH, 1);
                        ts->pendown = true;
                        dev_vdbg(&ts->spi->dev, "DOWN\n");
                }

                input_report_abs(input, ABS_X, x);
                input_report_abs(input, ABS_Y, y);
                input_report_abs(input, ABS_PRESSURE, ts->pressure_max - Rt);

                input_sync(input);
                dev_vdbg(&ts->spi->dev, "%4d/%4d/%4d\n", x, y, Rt);
        }
}

static irqreturn_t ads7846_hard_irq(int irq, void *handle)
{
        struct ads7846 *ts = handle;

        return get_pendown_state(ts) ? IRQ_WAKE_THREAD : IRQ_HANDLED;
}


static irqreturn_t ads7846_irq(int irq, void *handle)
{
        struct ads7846 *ts = handle;

        /* Start with a small delay before checking pendown state */
        msleep(TS_POLL_DELAY);

        while (!ts->stopped && get_pendown_state(ts)) {

                /* pen is down, continue with the measurement */
                ads7846_read_state(ts);

                if (!ts->stopped)
                        ads7846_report_state(ts);

                wait_event_timeout(ts->wait, ts->stopped,
                                   msecs_to_jiffies(TS_POLL_PERIOD));
        }

        if (ts->pendown) {
                struct input_dev *input = ts->input;

                input_report_key(input, BTN_TOUCH, 0);
                input_report_abs(input, ABS_PRESSURE, 0);
                input_sync(input);

                ts->pendown = false;
                dev_vdbg(&ts->spi->dev, "UP\n");
        }

        return IRQ_HANDLED;
}

#ifdef CONFIG_PM_SLEEP
static int ads7846_suspend(struct device *dev)
{
        struct ads7846 *ts = dev_get_drvdata(dev);

        mutex_lock(&ts->lock);

        if (!ts->suspended) {

                if (!ts->disabled)
                        __ads7846_disable(ts);

                if (device_may_wakeup(&ts->spi->dev))
                        enable_irq_wake(ts->spi->irq);

                ts->suspended = true;
        }

        mutex_unlock(&ts->lock);

        return 0;
}

static int ads7846_resume(struct device *dev)
{
        struct ads7846 *ts = dev_get_drvdata(dev);

        mutex_lock(&ts->lock);

        if (ts->suspended) {

                ts->suspended = false;

                if (device_may_wakeup(&ts->spi->dev))
                        disable_irq_wake(ts->spi->irq);

                if (!ts->disabled)
                        __ads7846_enable(ts);
        }

        mutex_unlock(&ts->lock);

        return 0;
}
#endif

static SIMPLE_DEV_PM_OPS(ads7846_pm, ads7846_suspend, ads7846_resume);

static int ads7846_setup_pendown(struct spi_device *spi,
                                 struct ads7846 *ts,
                                 const struct ads7846_platform_data *pdata)
{
        int err;

        /*
         * REVISIT when the irq can be triggered active-low, or if for some
         * reason the touchscreen isn't hooked up, we don't need to access
         * the pendown state.
         */

        if (pdata->get_pendown_state) {
                ts->get_pendown_state = pdata->get_pendown_state;
        } else if (gpio_is_valid(pdata->gpio_pendown)) {

                err = gpio_request_one(pdata->gpio_pendown, GPIOF_IN,
                                       "ads7846_pendown");
                if (err) {
                        dev_err(&spi->dev,
                                "failed to request/setup pendown GPIO%d: %d\n",
                                pdata->gpio_pendown, err);
                        return err;
                }

                ts->gpio_pendown = pdata->gpio_pendown;

                if (pdata->gpio_pendown_debounce)
                        gpio_set_debounce(pdata->gpio_pendown,
                                          pdata->gpio_pendown_debounce);
        } else {
                dev_err(&spi->dev, "no get_pendown_state nor gpio_pendown?\n");
                return -EINVAL;
        }

        return 0;
}

/*
 * Set up the transfers to read touchscreen state; this assumes we
 * use formula #2 for pressure, not #3.
 */
static void ads7846_setup_spi_msg(struct ads7846 *ts,
                                  const struct ads7846_platform_data *pdata)
{
        struct spi_message *m = &ts->msg[0];
        struct spi_transfer *x = ts->xfer;
        struct ads7846_packet *packet = ts->packet;
        int vref = pdata->keep_vref_on;

        if (ts->model == 7873) {
                /*
                 * The AD7873 is almost identical to the ADS7846
                 * keep VREF off during differential/ratiometric
                 * conversion modes.
                 */
                ts->model = 7846;
                vref = 0;
        }

        ts->msg_count = 1;
        spi_message_init(m);
        m->context = ts;

        if (ts->model == 7845) {
                packet->read_y_cmd[0] = READ_Y(vref);
                packet->read_y_cmd[1] = 0;
                packet->read_y_cmd[2] = 0;
                x->tx_buf = &packet->read_y_cmd[0];
                x->rx_buf = &packet->tc.y_buf[0];
                x->len = 3;
                spi_message_add_tail(x, m);
        } else {
                /* y- still on; turn on only y+ (and ADC) */
                packet->read_y = READ_Y(vref);
                x->tx_buf = &packet->read_y;
                x->len = 1;
                spi_message_add_tail(x, m);

                x++;
                x->rx_buf = &packet->tc.y;
                x->len = 2;
                spi_message_add_tail(x, m);
        }

        /*
         * The first sample after switching drivers can be low quality;
         * optionally discard it, using a second one after the signals
         * have had enough time to stabilize.
         */
        if (pdata->settle_delay_usecs) {
                x->delay_usecs = pdata->settle_delay_usecs;

                x++;
                x->tx_buf = &packet->read_y;
                x->len = 1;
                spi_message_add_tail(x, m);

                x++;
                x->rx_buf = &packet->tc.y;
                x->len = 2;
                spi_message_add_tail(x, m);
        }

        ts->msg_count++;
        m++;
        spi_message_init(m);
        m->context = ts;

        if (ts->model == 7845) {
                x++;
                packet->read_x_cmd[0] = READ_X(vref);
                packet->read_x_cmd[1] = 0;
                packet->read_x_cmd[2] = 0;
                x->tx_buf = &packet->read_x_cmd[0];
                x->rx_buf = &packet->tc.x_buf[0];
                x->len = 3;
                spi_message_add_tail(x, m);
        } else {
                /* turn y- off, x+ on, then leave in lowpower */
                x++;
                packet->read_x = READ_X(vref);
                x->tx_buf = &packet->read_x;
                x->len = 1;
                spi_message_add_tail(x, m);

                x++;
                x->rx_buf = &packet->tc.x;
                x->len = 2;
                spi_message_add_tail(x, m);
        }

        /* ... maybe discard first sample ... */
        if (pdata->settle_delay_usecs) {
                x->delay_usecs = pdata->settle_delay_usecs;

                x++;
                x->tx_buf = &packet->read_x;
                x->len = 1;
                spi_message_add_tail(x, m);

                x++;
                x->rx_buf = &packet->tc.x;
                x->len = 2;
                spi_message_add_tail(x, m);
        }

        /* turn y+ off, x- on; we'll use formula #2 */
        if (ts->model == 7846) {
                ts->msg_count++;
                m++;
                spi_message_init(m);
                m->context = ts;

                x++;
                packet->read_z1 = READ_Z1(vref);
                x->tx_buf = &packet->read_z1;
                x->len = 1;
                spi_message_add_tail(x, m);

                x++;
                x->rx_buf = &packet->tc.z1;
                x->len = 2;
                spi_message_add_tail(x, m);

                /* ... maybe discard first sample ... */
                if (pdata->settle_delay_usecs) {
                        x->delay_usecs = pdata->settle_delay_usecs;

                        x++;
                        x->tx_buf = &packet->read_z1;
                        x->len = 1;
                        spi_message_add_tail(x, m);

                        x++;
                        x->rx_buf = &packet->tc.z1;
                        x->len = 2;
                        spi_message_add_tail(x, m);
                }

                ts->msg_count++;
                m++;
                spi_message_init(m);
                m->context = ts;

                x++;
                packet->read_z2 = READ_Z2(vref);
                x->tx_buf = &packet->read_z2;
                x->len = 1;
                spi_message_add_tail(x, m);

                x++;
                x->rx_buf = &packet->tc.z2;
                x->len = 2;
                spi_message_add_tail(x, m);

                /* ... maybe discard first sample ... */
                if (pdata->settle_delay_usecs) {
                        x->delay_usecs = pdata->settle_delay_usecs;

                        x++;
                        x->tx_buf = &packet->read_z2;
                        x->len = 1;
                        spi_message_add_tail(x, m);

                        x++;
                        x->rx_buf = &packet->tc.z2;
                        x->len = 2;
                        spi_message_add_tail(x, m);
                }
        }

        /* power down */
        ts->msg_count++;
        m++;
        spi_message_init(m);
        m->context = ts;

        if (ts->model == 7845) {
                x++;
                packet->pwrdown_cmd[0] = PWRDOWN;
                packet->pwrdown_cmd[1] = 0;
                packet->pwrdown_cmd[2] = 0;
                x->tx_buf = &packet->pwrdown_cmd[0];
                x->len = 3;
        } else {
                x++;
                packet->pwrdown = PWRDOWN;
                x->tx_buf = &packet->pwrdown;
                x->len = 1;
                spi_message_add_tail(x, m);

                x++;
                x->rx_buf = &packet->dummy;
                x->len = 2;
        }

        CS_CHANGE(*x);
        spi_message_add_tail(x, m);
}

#ifdef CONFIG_OF
static const struct of_device_id ads7846_dt_ids[] = {
        { .compatible = "ti,tsc2046",   .data = (void *) 7846 },
        { .compatible = "ti,ads7843",   .data = (void *) 7843 },
        { .compatible = "ti,ads7845",   .data = (void *) 7845 },
        { .compatible = "ti,ads7846",   .data = (void *) 7846 },
        { .compatible = "ti,ads7873",   .data = (void *) 7873 },
        { }
};
MODULE_DEVICE_TABLE(of, ads7846_dt_ids);

static const struct ads7846_platform_data *ads7846_probe_dt(struct device *dev)
{
        struct ads7846_platform_data *pdata;
        struct device_node *node = dev->of_node;
        const struct of_device_id *match;

        if (!node) {
                dev_err(dev, "Device does not have associated DT data\n");
                return ERR_PTR(-EINVAL);
        }

        match = of_match_device(ads7846_dt_ids, dev);
        if (!match) {
                dev_err(dev, "Unknown device model\n");
                return ERR_PTR(-EINVAL);
        }

        pdata = devm_kzalloc(dev, sizeof(*pdata), GFP_KERNEL);
        if (!pdata)
                return ERR_PTR(-ENOMEM);

        pdata->model = (unsigned long)match->data;

        of_property_read_u16(node, "ti,vref-delay-usecs",
                             &pdata->vref_delay_usecs);
        of_property_read_u16(node, "ti,vref-mv", &pdata->vref_mv);
        pdata->keep_vref_on = of_property_read_bool(node, "ti,keep-vref-on");

        pdata->swap_xy = of_property_read_bool(node, "ti,swap-xy");

        of_property_read_u16(node, "ti,settle-delay-usec",
                             &pdata->settle_delay_usecs);
        of_property_read_u16(node, "ti,penirq-recheck-delay-usecs",
                             &pdata->penirq_recheck_delay_usecs);

        of_property_read_u16(node, "ti,x-plate-ohms", &pdata->x_plate_ohms);
        of_property_read_u16(node, "ti,y-plate-ohms", &pdata->y_plate_ohms);

        of_property_read_u16(node, "ti,x-min", &pdata->x_min);
        of_property_read_u16(node, "ti,y-min", &pdata->y_min);
        of_property_read_u16(node, "ti,x-max", &pdata->x_max);
        of_property_read_u16(node, "ti,y-max", &pdata->y_max);

        of_property_read_u16(node, "ti,pressure-min", &pdata->pressure_min);
        of_property_read_u16(node, "ti,pressure-max", &pdata->pressure_max);

        of_property_read_u16(node, "ti,debounce-max", &pdata->debounce_max);
        of_property_read_u16(node, "ti,debounce-tol", &pdata->debounce_tol);
        of_property_read_u16(node, "ti,debounce-rep", &pdata->debounce_rep);

        of_property_read_u32(node, "ti,pendown-gpio-debounce",
                             &pdata->gpio_pendown_debounce);

        pdata->wakeup = of_property_read_bool(node, "linux,wakeup");

        pdata->gpio_pendown = of_get_named_gpio(dev->of_node, "pendown-gpio", 0);

        return pdata;
}
#else
static const struct ads7846_platform_data *ads7846_probe_dt(struct device *dev)
{
        dev_err(dev, "no platform data defined\n");
        return ERR_PTR(-EINVAL);
}
#endif

static int ads7846_probe(struct spi_device *spi)
{
        const struct ads7846_platform_data *pdata;
        struct ads7846 *ts;
        struct ads7846_packet *packet;
        struct input_dev *input_dev;
        unsigned long irq_flags;
        int err;

        if (!spi->irq) {
                dev_dbg(&spi->dev, "no IRQ?\n");
                return -EINVAL;
        }

        /* don't exceed max specified sample rate */
        if (spi->max_speed_hz > (125000 * SAMPLE_BITS)) {
                dev_err(&spi->dev, "f(sample) %d KHz?\n",
                                (spi->max_speed_hz/SAMPLE_BITS)/1000);
                return -EINVAL;
        }

        /*
         * We'd set TX word size 8 bits and RX word size to 13 bits ... except
         * that even if the hardware can do that, the SPI controller driver
         * may not.  So we stick to very-portable 8 bit words, both RX and TX.
         */
        spi->bits_per_word = 8;
        spi->mode = SPI_MODE_0;
        err = spi_setup(spi);
        if (err < 0)
                return err;

        ts = kzalloc(sizeof(struct ads7846), GFP_KERNEL);
        packet = kzalloc(sizeof(struct ads7846_packet), GFP_KERNEL);
        input_dev = input_allocate_device();
        if (!ts || !packet || !input_dev) {
                err = -ENOMEM;
                goto err_free_mem;
        }

        spi_set_drvdata(spi, ts);

        ts->packet = packet;
        ts->spi = spi;
        ts->input = input_dev;

        mutex_init(&ts->lock);
        init_waitqueue_head(&ts->wait);

        pdata = dev_get_platdata(&spi->dev);
        if (!pdata) {
                pdata = ads7846_probe_dt(&spi->dev);
                if (IS_ERR(pdata))
                        return PTR_ERR(pdata);
        }

        ts->model = pdata->model ? : 7846;
        ts->vref_delay_usecs = pdata->vref_delay_usecs ? : 100;
        ts->x_plate_ohms = pdata->x_plate_ohms ? : 400;
        ts->pressure_max = pdata->pressure_max ? : ~0;

        ts->vref_mv = pdata->vref_mv;
        ts->swap_xy = pdata->swap_xy;

        if (pdata->filter != NULL) {
                if (pdata->filter_init != NULL) {
                        err = pdata->filter_init(pdata, &ts->filter_data);
                        if (err < 0)
                                goto err_free_mem;
                }
                ts->filter = pdata->filter;
                ts->filter_cleanup = pdata->filter_cleanup;
        } else if (pdata->debounce_max) {
                ts->debounce_max = pdata->debounce_max;
                if (ts->debounce_max < 2)
                        ts->debounce_max = 2;
                ts->debounce_tol = pdata->debounce_tol;
                ts->debounce_rep = pdata->debounce_rep;
                ts->filter = ads7846_debounce_filter;
                ts->filter_data = ts;
        } else {
                ts->filter = ads7846_no_filter;
        }

        err = ads7846_setup_pendown(spi, ts, pdata);
        if (err)
                goto err_cleanup_filter;

        if (pdata->penirq_recheck_delay_usecs)
                ts->penirq_recheck_delay_usecs =
                                pdata->penirq_recheck_delay_usecs;

        ts->wait_for_sync = pdata->wait_for_sync ? : null_wait_for_sync;

        snprintf(ts->phys, sizeof(ts->phys), "%s/input0", dev_name(&spi->dev));
        snprintf(ts->name, sizeof(ts->name), "ADS%d Touchscreen", ts->model);

        input_dev->name = ts->name;
        input_dev->phys = ts->phys;
        input_dev->dev.parent = &spi->dev;

        input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
        input_dev->keybit[BIT_WORD(BTN_TOUCH)] = BIT_MASK(BTN_TOUCH);
        input_set_abs_params(input_dev, ABS_X,
                        pdata->x_min ? : 0,
                        pdata->x_max ? : MAX_12BIT,
                        0, 0);
        input_set_abs_params(input_dev, ABS_Y,
                        pdata->y_min ? : 0,
                        pdata->y_max ? : MAX_12BIT,
                        0, 0);
        input_set_abs_params(input_dev, ABS_PRESSURE,
                        pdata->pressure_min, pdata->pressure_max, 0, 0);

        ads7846_setup_spi_msg(ts, pdata);

        ts->reg = regulator_get(&spi->dev, "vcc");
        if (IS_ERR(ts->reg)) {
                err = PTR_ERR(ts->reg);
                dev_err(&spi->dev, "unable to get regulator: %d\n", err);
                goto err_free_gpio;
        }

        err = regulator_enable(ts->reg);
        if (err) {
                dev_err(&spi->dev, "unable to enable regulator: %d\n", err);
                goto err_put_regulator;
        }

        irq_flags = pdata->irq_flags ? : IRQF_TRIGGER_FALLING;
        irq_flags |= IRQF_ONESHOT;

        err = request_threaded_irq(spi->irq, ads7846_hard_irq, ads7846_irq,
                                   irq_flags, spi->dev.driver->name, ts);
        if (err && !pdata->irq_flags) {
                dev_info(&spi->dev,
                        "trying pin change workaround on irq %d\n", spi->irq);
                irq_flags |= IRQF_TRIGGER_RISING;
                err = request_threaded_irq(spi->irq,
                                  ads7846_hard_irq, ads7846_irq,
                                  irq_flags, spi->dev.driver->name, ts);
        }

        if (err) {
                dev_dbg(&spi->dev, "irq %d busy?\n", spi->irq);
                goto err_disable_regulator;
        }

        err = ads784x_hwmon_register(spi, ts);
        if (err)
                goto err_free_irq;

        dev_info(&spi->dev, "touchscreen, irq %d\n", spi->irq);

        /*
         * Take a first sample, leaving nPENIRQ active and vREF off; avoid
         * the touchscreen, in case it's not connected.
         */
        if (ts->model == 7845)
                ads7845_read12_ser(&spi->dev, PWRDOWN);
        else
                (void) ads7846_read12_ser(&spi->dev, READ_12BIT_SER(vaux));

        err = sysfs_create_group(&spi->dev.kobj, &ads784x_attr_group);
        if (err)
                goto err_remove_hwmon;

        err = input_register_device(input_dev);
        if (err)
                goto err_remove_attr_group;

        device_init_wakeup(&spi->dev, pdata->wakeup);

        /*
         * If device does not carry platform data we must have allocated it
         * when parsing DT data.
         */
        if (!dev_get_platdata(&spi->dev))
                devm_kfree(&spi->dev, (void *)pdata);

        return 0;

 err_remove_attr_group:
        sysfs_remove_group(&spi->dev.kobj, &ads784x_attr_group);
 err_remove_hwmon:
        ads784x_hwmon_unregister(spi, ts);
 err_free_irq:
        free_irq(spi->irq, ts);
 err_disable_regulator:
        regulator_disable(ts->reg);
 err_put_regulator:
        regulator_put(ts->reg);
 err_free_gpio:
        if (!ts->get_pendown_state)
                gpio_free(ts->gpio_pendown);
 err_cleanup_filter:
        if (ts->filter_cleanup)
                ts->filter_cleanup(ts->filter_data);
 err_free_mem:
        input_free_device(input_dev);
        kfree(packet);
        kfree(ts);
        return err;
}

static int ads7846_remove(struct spi_device *spi)
{
        struct ads7846 *ts = spi_get_drvdata(spi);

        device_init_wakeup(&spi->dev, false);

        sysfs_remove_group(&spi->dev.kobj, &ads784x_attr_group);

        ads7846_disable(ts);
        free_irq(ts->spi->irq, ts);

        input_unregister_device(ts->input);

        ads784x_hwmon_unregister(spi, ts);

        regulator_disable(ts->reg);
        regulator_put(ts->reg);

        if (!ts->get_pendown_state) {
                /*
                 * If we are not using specialized pendown method we must
                 * have been relying on gpio we set up ourselves.
                 */
                gpio_free(ts->gpio_pendown);
        }

        if (ts->filter_cleanup)
                ts->filter_cleanup(ts->filter_data);

        kfree(ts->packet);
        kfree(ts);

        dev_dbg(&spi->dev, "unregistered touchscreen\n");

        return 0;
}

static struct spi_driver ads7846_driver = {
        .driver = {
                .name   = "ads7846",
                .owner  = THIS_MODULE,
                .pm     = &ads7846_pm,
                .of_match_table = of_match_ptr(ads7846_dt_ids),
        },
        .probe          = ads7846_probe,
        .remove         = ads7846_remove,
};

module_spi_driver(ads7846_driver);

MODULE_DESCRIPTION("ADS7846 TouchScreen Driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("spi:ads7846");