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#include <linux/init.h>

#include <linux/module.h>

#include <linux/fs.h>

#include <linux/cdev.h>

#include <linux/slab.h>

#include <linux/device.h>

#include <linux/semaphore.h>

#include <linux/interrupt.h>

#include <linux/gpio.h>

#include <asm/atomic.h>

MODULE_AUTHOR("Tom Mullins");

MODULE_LICENSE("GPL");

#define N_ENCODERS 4

const int enc_pins[N_ENCODERS][2] = {{78, 79}, {80, 81}, {82, 83}, {84, 85}};

struct class *enc_class = NULL;

struct encoder_device

{

  struct device *device;

  int pins[2];

  int irq[2];

  int status;

  atomic_t value;

  dev_t dev;

}

encs[N_ENCODERS];

static ssize_t enc_show(struct device *dev, struct device_attribute *attr,

    char *buf);

static ssize_t enc_store(struct device *dev, struct device_attribute *attr,

    const char *buf, size_t count);

static void enc_free(struct encoder_device *enc);

static int enc_init(dev_t dev, struct encoder_device *enc, const int *pins);

DEVICE_ATTR(ticks, S_IWUSR | S_IRUGO, enc_show, enc_store);

static ssize_t enc_show(struct device *dev, struct device_attribute *attr,

    char *buf)

{

  size_t nwritten;

  struct encoder_device *enc = dev_get_drvdata(dev);

  nwritten = scnprintf(buf, PAGE_SIZE, "%d\n", atomic_read(&enc->value));

  return nwritten;

}

static ssize_t enc_store(struct device *dev, struct device_attribute *attr,

    const char *buf, size_t count)

{

  char *end;

  struct encoder_device *enc = dev_get_drvdata(dev);

  atomic_set(&enc->value, simple_strtol(buf, &end, 10));

  return count;

}

irqreturn_t intA(int irq, void *encp) {

  struct encoder_device *enc = encp;

  int this = gpio_get_value(enc->pins[0]);

  int other = gpio_get_value(enc->pins[1]);

  if (this == other) {

    atomic_inc(&enc->value);

  } else {

    atomic_dec(&enc->value);

  }

  return IRQ_HANDLED;

}

irqreturn_t intB(int irq, void *encp) {

  struct encoder_device *enc = encp;

  int this = gpio_get_value(enc->pins[1]);

  int other = gpio_get_value(enc->pins[0]);

  if (this == other) {

    atomic_dec(&enc->value);

  } else {

    atomic_inc(&enc->value);

  }

  return IRQ_HANDLED;

}

static int enc_init(dev_t dev, struct encoder_device *enc, const int *pins)

{

  int i, err;

  // initialize members

  enc->dev = dev;

  enc->status = 0;

  // register gpio and interrupts

  for (i = 0; i < 2; i++) {

    enc->pins[i] = pins[i];

    enc->irq[i] = gpio_to_irq(pins[i]);

    if (enc->irq[i] < 0) {

      printk("Error %d requesting irq number for gpio %d\n", enc->irq[i],

          enc->pins[i]);

      return 1;

    }

    err = gpio_direction_input(enc->pins[i]);

    if (err < 0) {

      printk("Error %d setting gpio %d to input\n", err, enc->pins[i]);

      return 1;

    }

    err = request_irq(enc->irq[i], i? intB:intA, 0, "encoder", enc);

    if (err < 0) {

      printk("Error %d requesting irq %d\n", err, enc->irq[i]);

      return 1;

    }

    err = irq_set_irq_type(enc->irq[i], IRQ_TYPE_EDGE_BOTH);

    if (err < 0) {

      printk("Error %d setting irq %d type\n", err, enc->irq[i]);

      return 1;

    }

    // TODO the error checking here does not properly clean up after itself

    // TODO perhaps we should use gpio_request? probably not necessary...

  }

  enc->status = 2;

  return 0;

}

int enc_create_dev(struct encoder_device *enc) {

  int err;

  // make file in /dev

  enc->device = device_create(enc_class, NULL, enc->dev, enc, "enc%d",

      MINOR(enc->dev));

  if (IS_ERR(enc->device))

  {

    err = PTR_ERR(enc->device);

    enc->device = NULL;

    enc_free(enc);

    return err;

  }

  enc->status = 3;

  device_create_file(enc->device, &dev_attr_ticks);

  // TODO error check

  enc->status = 4;

  return 0;

}

static void enc_free(struct encoder_device *enc)

{

  switch (enc->status)

  {

    case 4:

      device_remove_file(enc->device, &dev_attr_ticks);

    case 3:

      device_destroy(enc_class, enc->dev);

      enc->device = NULL;

    case 2:

      free_irq(enc->irq[0], enc);

      free_irq(enc->irq[1], enc);

  }

  enc->status = 0;

}

static void enc_exit_module(void)

{

  int i;

  for (i = 0; i < N_ENCODERS; i++)

  {

    enc_free(&encs[i]);

  }

  if (enc_class) {

    class_destroy(enc_class);

    enc_class = NULL;

  }

}

module_exit(enc_exit_module);

static int __init enc_init_module(void)

{

  int i, err;

  // initialize enc structures

  for (i = 0; i < N_ENCODERS; i++) {

    err = enc_init(MKDEV(0, i), &encs[i], enc_pins[i]);

    if (err)

    {

      printk(KERN_WARNING "Error %d initializing encoder %d\n", err, i);

      enc_exit_module();

      return err;

    }

  }

  // register our device class for files in /dev

  enc_class = class_create(THIS_MODULE, "encoder");

  if (IS_ERR(enc_class))

  {

    err = PTR_ERR(enc_class);

    enc_class = NULL;

    printk(KERN_WARNING "Error %d creating device class\n", err);

  }

  else

  {

    // create each device

    for (i = 0; i < N_ENCODERS; i++) {

      err = enc_create_dev(&encs[i]);

      if (err)

      {

        printk(KERN_WARNING "Error %d creating enc%d\n", err, i);

        enc_exit_module();

        return err;

      }

    }

  }

  return 0;

}

module_init(enc_init_module);