// SPDX-License-Identifier: GPL-2.0-only

  /*
   * 	NetWinder Button Driver-
   *	Copyright (C) Alex Holden <alex@linuxhacker.org> 1998, 1999.
   *
   */

  #include <linux/module.h>
  #include <linux/kernel.h>

  #include <linux/sched/signal.h>

  #include <linux/interrupt.h>
  #include <linux/time.h>
  #include <linux/timer.h>
  #include <linux/fs.h>
  #include <linux/miscdevice.h>
  #include <linux/string.h>
  #include <linux/errno.h>
  #include <linux/init.h>

  #include <linux/uaccess.h>

  #include <asm/irq.h>
  #include <asm/mach-types.h>
  
  #define __NWBUTTON_C		/* Tell the header file who we are */
  #include "nwbutton.h"

  static void button_sequence_finished(struct timer_list *unused);

  static int button_press_count;		/* The count of button presses */

  /* Times for the end of a sequence */

  static DEFINE_TIMER(button_timer, button_sequence_finished);

  static DECLARE_WAIT_QUEUE_HEAD(button_wait_queue); /* Used for blocking read */
  static char button_output_buffer[32];	/* Stores data to write out of device */
  static int bcount;			/* The number of bytes in the buffer */
  static int bdelay = BUTTON_DELAY;	/* The delay, in jiffies */
  static struct button_callback button_callback_list[32]; /* The callback list */
  static int callback_count;		/* The number of callbacks registered */
  static int reboot_count = NUM_PRESSES_REBOOT; /* Number of presses to reboot */
  
  /*
   * This function is called by other drivers to register a callback function
   * to be called when a particular number of button presses occurs.
   * The callback list is a static array of 32 entries (I somehow doubt many
   * people are ever going to want to register more than 32 different actions
   * to be performed by the kernel on different numbers of button presses ;).
   * However, if an attempt to register a 33rd entry (perhaps a stuck loop
   * somewhere registering the same entry over and over?) it will fail to
   * do so and return -ENOMEM. If an attempt is made to register a null pointer,
   * it will fail to do so and return -EINVAL.
   * Because callbacks can be unregistered at random the list can become
   * fragmented, so we need to search through the list until we find the first
   * free entry.
   *
   * FIXME: Has anyone spotted any locking functions int his code recently ??
   */
  
  int button_add_callback (void (*callback) (void), int count)
  {
  	int lp = 0;
  	if (callback_count == 32) {
  		return -ENOMEM;
  	}
  	if (!callback) {
  		return -EINVAL;
  	}
  	callback_count++;
  	for (; (button_callback_list [lp].callback); lp++);
  	button_callback_list [lp].callback = callback;
  	button_callback_list [lp].count = count;
  	return 0;
  }
  
  /*
   * This function is called by other drivers to deregister a callback function.
   * If you attempt to unregister a callback which does not exist, it will fail
   * with -EINVAL. If there is more than one entry with the same address,
   * because it searches the list from end to beginning, it will unregister the
   * last one to be registered first (FILO- First In Last Out).

   * Note that this is not necessarily true if the entries are not submitted

   * at the same time, because another driver could have unregistered a callback
   * between the submissions creating a gap earlier in the list, which would
   * be filled first at submission time.
   */
  
  int button_del_callback (void (*callback) (void))
  {
  	int lp = 31;
  	if (!callback) {
  		return -EINVAL;
  	}
  	while (lp >= 0) {
  		if ((button_callback_list [lp].callback) == callback) {
  			button_callback_list [lp].callback = NULL;
  			button_callback_list [lp].count = 0;
  			callback_count--;
  			return 0;

  		}

  		lp--;

  	}

  	return -EINVAL;
  }
  
  /*
   * This function is called by button_sequence_finished to search through the
   * list of callback functions, and call any of them whose count argument
   * matches the current count of button presses. It starts at the beginning
   * of the list and works up to the end. It will refuse to follow a null
   * pointer (which should never happen anyway).
   */
  
  static void button_consume_callbacks (int bpcount)
  {
  	int lp = 0;
  	for (; lp <= 31; lp++) {
  		if ((button_callback_list [lp].count) == bpcount) {
  			if (button_callback_list [lp].callback) {
  				button_callback_list[lp].callback();
  			}
  		}
  	}
  }
  
  /* 
   * This function is called when the button_timer times out.
   * ie. When you don't press the button for bdelay jiffies, this is taken to
   * mean you have ended the sequence of key presses, and this function is
   * called to wind things up (write the press_count out to /dev/button, call
   * any matching registered function callbacks, initiate reboot, etc.).
   */

  static void button_sequence_finished(struct timer_list *unused)

  {

  	if (IS_ENABLED(CONFIG_NWBUTTON_REBOOT) &&
  	    button_press_count == reboot_count)

  		kill_cad_pid(SIGINT, 1);	/* Ask init to reboot us */

  	button_consume_callbacks (button_press_count);
  	bcount = sprintf (button_output_buffer, "%d
  ", button_press_count);
  	button_press_count = 0;		/* Reset the button press counter */
  	wake_up_interruptible (&button_wait_queue);
  }
  
  /* 
   *  This handler is called when the orange button is pressed (GPIO 10 of the
   *  SuperIO chip, which maps to logical IRQ 26). If the press_count is 0,
   *  this is the first press, so it starts a timer and increments the counter.
   *  If it is higher than 0, it deletes the old timer, starts a new one, and
   *  increments the counter.
   */ 

  static irqreturn_t button_handler (int irq, void *dev_id)

  {

  	button_press_count++;

  	mod_timer(&button_timer, jiffies + bdelay);

  
  	return IRQ_HANDLED;
  }
  
  /*
   * This function is called when a user space program attempts to read
   * /dev/nwbutton. It puts the device to sleep on the wait queue until
   * button_sequence_finished writes some data to the buffer and flushes
   * the queue, at which point it writes the data out to the device and
   * returns the number of characters it has written. This function is
   * reentrant, so that many processes can be attempting to read from the
   * device at any one time.
   */
  
  static int button_read (struct file *filp, char __user *buffer,
  			size_t count, loff_t *ppos)
  {

  	DEFINE_WAIT(wait);
  	prepare_to_wait(&button_wait_queue, &wait, TASK_INTERRUPTIBLE);
  	schedule();
  	finish_wait(&button_wait_queue, &wait);

  	return (copy_to_user (buffer, &button_output_buffer, bcount))
  		 ? -EFAULT : bcount;
  }
  
  /* 
   * This structure is the file operations structure, which specifies what
   * callbacks functions the kernel should call when a user mode process
   * attempts to perform these operations on the device.
   */

  static const struct file_operations button_fops = {

  	.owner		= THIS_MODULE,
  	.read		= button_read,

  	.llseek		= noop_llseek,

  };
  
  /* 
   * This structure is the misc device structure, which specifies the minor
   * device number (158 in this case), the name of the device (for /proc/misc),
   * and the address of the above file operations structure.
   */
  
  static struct miscdevice button_misc_device = {
  	BUTTON_MINOR,
  	"nwbutton",
  	&button_fops,
  };
  
  /*
   * This function is called to initialise the driver, either from misc.c at
   * bootup if the driver is compiled into the kernel, or from init_module
   * below at module insert time. It attempts to register the device node
   * and the IRQ and fails with a warning message if either fails, though
   * neither ever should because the device number and IRQ are unique to
   * this driver.
   */
  
  static int __init nwbutton_init(void)
  {
  	if (!machine_is_netwinder())
  		return -ENODEV;
  
  	printk (KERN_INFO "NetWinder Button Driver Version %s (C) Alex Holden "
  			"<alex@linuxhacker.org> 1998.
  ", VERSION);
  
  	if (misc_register (&button_misc_device)) {
  		printk (KERN_WARNING "nwbutton: Couldn't register device 10, "
  				"%d.
  ", BUTTON_MINOR);
  		return -EBUSY;
  	}

  	if (request_irq (IRQ_NETWINDER_BUTTON, button_handler, 0,

  			"nwbutton", NULL)) {
  		printk (KERN_WARNING "nwbutton: IRQ %d is not free.
  ",
  				IRQ_NETWINDER_BUTTON);
  		misc_deregister (&button_misc_device);
  		return -EIO;
  	}
  	return 0;
  }
  
  static void __exit nwbutton_exit (void) 
  {
  	free_irq (IRQ_NETWINDER_BUTTON, NULL);
  	misc_deregister (&button_misc_device);
  }
  
  
  MODULE_AUTHOR("Alex Holden");
  MODULE_LICENSE("GPL");
  
  module_init(nwbutton_init);
  module_exit(nwbutton_exit);