linux/drivers/char/nwbutton.c
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   1/*
   2 *      NetWinder Button Driver-
   3 *      Copyright (C) Alex Holden <alex@linuxhacker.org> 1998, 1999.
   4 *
   5 */
   6
   7#include <linux/module.h>
   8#include <linux/kernel.h>
   9#include <linux/sched.h>
  10#include <linux/interrupt.h>
  11#include <linux/time.h>
  12#include <linux/timer.h>
  13#include <linux/fs.h>
  14#include <linux/miscdevice.h>
  15#include <linux/string.h>
  16#include <linux/errno.h>
  17#include <linux/init.h>
  18
  19#include <asm/uaccess.h>
  20#include <asm/irq.h>
  21#include <asm/mach-types.h>
  22
  23#define __NWBUTTON_C            /* Tell the header file who we are */
  24#include "nwbutton.h"
  25
  26static void button_sequence_finished (unsigned long parameters);
  27
  28static int button_press_count;          /* The count of button presses */
  29/* Times for the end of a sequence */
  30static DEFINE_TIMER(button_timer, button_sequence_finished, 0, 0);
  31static DECLARE_WAIT_QUEUE_HEAD(button_wait_queue); /* Used for blocking read */
  32static char button_output_buffer[32];   /* Stores data to write out of device */
  33static int bcount;                      /* The number of bytes in the buffer */
  34static int bdelay = BUTTON_DELAY;       /* The delay, in jiffies */
  35static struct button_callback button_callback_list[32]; /* The callback list */
  36static int callback_count;              /* The number of callbacks registered */
  37static int reboot_count = NUM_PRESSES_REBOOT; /* Number of presses to reboot */
  38
  39/*
  40 * This function is called by other drivers to register a callback function
  41 * to be called when a particular number of button presses occurs.
  42 * The callback list is a static array of 32 entries (I somehow doubt many
  43 * people are ever going to want to register more than 32 different actions
  44 * to be performed by the kernel on different numbers of button presses ;).
  45 * However, if an attempt to register a 33rd entry (perhaps a stuck loop
  46 * somewhere registering the same entry over and over?) it will fail to
  47 * do so and return -ENOMEM. If an attempt is made to register a null pointer,
  48 * it will fail to do so and return -EINVAL.
  49 * Because callbacks can be unregistered at random the list can become
  50 * fragmented, so we need to search through the list until we find the first
  51 * free entry.
  52 *
  53 * FIXME: Has anyone spotted any locking functions int his code recently ??
  54 */
  55
  56int button_add_callback (void (*callback) (void), int count)
  57{
  58        int lp = 0;
  59        if (callback_count == 32) {
  60                return -ENOMEM;
  61        }
  62        if (!callback) {
  63                return -EINVAL;
  64        }
  65        callback_count++;
  66        for (; (button_callback_list [lp].callback); lp++);
  67        button_callback_list [lp].callback = callback;
  68        button_callback_list [lp].count = count;
  69        return 0;
  70}
  71
  72/*
  73 * This function is called by other drivers to deregister a callback function.
  74 * If you attempt to unregister a callback which does not exist, it will fail
  75 * with -EINVAL. If there is more than one entry with the same address,
  76 * because it searches the list from end to beginning, it will unregister the
  77 * last one to be registered first (FILO- First In Last Out).
  78 * Note that this is not necessarily true if the entries are not submitted
  79 * at the same time, because another driver could have unregistered a callback
  80 * between the submissions creating a gap earlier in the list, which would
  81 * be filled first at submission time.
  82 */
  83
  84int button_del_callback (void (*callback) (void))
  85{
  86        int lp = 31;
  87        if (!callback) {
  88                return -EINVAL;
  89        }
  90        while (lp >= 0) {
  91                if ((button_callback_list [lp].callback) == callback) {
  92                        button_callback_list [lp].callback = NULL;
  93                        button_callback_list [lp].count = 0;
  94                        callback_count--;
  95                        return 0;
  96                }
  97                lp--;
  98        }
  99        return -EINVAL;
 100}
 101
 102/*
 103 * This function is called by button_sequence_finished to search through the
 104 * list of callback functions, and call any of them whose count argument
 105 * matches the current count of button presses. It starts at the beginning
 106 * of the list and works up to the end. It will refuse to follow a null
 107 * pointer (which should never happen anyway).
 108 */
 109
 110static void button_consume_callbacks (int bpcount)
 111{
 112        int lp = 0;
 113        for (; lp <= 31; lp++) {
 114                if ((button_callback_list [lp].count) == bpcount) {
 115                        if (button_callback_list [lp].callback) {
 116                                button_callback_list[lp].callback();
 117                        }
 118                }
 119        }
 120}
 121
 122/* 
 123 * This function is called when the button_timer times out.
 124 * ie. When you don't press the button for bdelay jiffies, this is taken to
 125 * mean you have ended the sequence of key presses, and this function is
 126 * called to wind things up (write the press_count out to /dev/button, call
 127 * any matching registered function callbacks, initiate reboot, etc.).
 128 */
 129
 130static void button_sequence_finished (unsigned long parameters)
 131{
 132#ifdef CONFIG_NWBUTTON_REBOOT           /* Reboot using button is enabled */
 133        if (button_press_count == reboot_count)
 134                kill_cad_pid(SIGINT, 1);        /* Ask init to reboot us */
 135#endif /* CONFIG_NWBUTTON_REBOOT */
 136        button_consume_callbacks (button_press_count);
 137        bcount = sprintf (button_output_buffer, "%d\n", button_press_count);
 138        button_press_count = 0;         /* Reset the button press counter */
 139        wake_up_interruptible (&button_wait_queue);
 140}
 141
 142/* 
 143 *  This handler is called when the orange button is pressed (GPIO 10 of the
 144 *  SuperIO chip, which maps to logical IRQ 26). If the press_count is 0,
 145 *  this is the first press, so it starts a timer and increments the counter.
 146 *  If it is higher than 0, it deletes the old timer, starts a new one, and
 147 *  increments the counter.
 148 */ 
 149
 150static irqreturn_t button_handler (int irq, void *dev_id)
 151{
 152        button_press_count++;
 153        mod_timer(&button_timer, jiffies + bdelay);
 154
 155        return IRQ_HANDLED;
 156}
 157
 158/*
 159 * This function is called when a user space program attempts to read
 160 * /dev/nwbutton. It puts the device to sleep on the wait queue until
 161 * button_sequence_finished writes some data to the buffer and flushes
 162 * the queue, at which point it writes the data out to the device and
 163 * returns the number of characters it has written. This function is
 164 * reentrant, so that many processes can be attempting to read from the
 165 * device at any one time.
 166 */
 167
 168static int button_read (struct file *filp, char __user *buffer,
 169                        size_t count, loff_t *ppos)
 170{
 171        interruptible_sleep_on (&button_wait_queue);
 172        return (copy_to_user (buffer, &button_output_buffer, bcount))
 173                 ? -EFAULT : bcount;
 174}
 175
 176/* 
 177 * This structure is the file operations structure, which specifies what
 178 * callbacks functions the kernel should call when a user mode process
 179 * attempts to perform these operations on the device.
 180 */
 181
 182static const struct file_operations button_fops = {
 183        .owner          = THIS_MODULE,
 184        .read           = button_read,
 185        .llseek         = noop_llseek,
 186};
 187
 188/* 
 189 * This structure is the misc device structure, which specifies the minor
 190 * device number (158 in this case), the name of the device (for /proc/misc),
 191 * and the address of the above file operations structure.
 192 */
 193
 194static struct miscdevice button_misc_device = {
 195        BUTTON_MINOR,
 196        "nwbutton",
 197        &button_fops,
 198};
 199
 200/*
 201 * This function is called to initialise the driver, either from misc.c at
 202 * bootup if the driver is compiled into the kernel, or from init_module
 203 * below at module insert time. It attempts to register the device node
 204 * and the IRQ and fails with a warning message if either fails, though
 205 * neither ever should because the device number and IRQ are unique to
 206 * this driver.
 207 */
 208
 209static int __init nwbutton_init(void)
 210{
 211        if (!machine_is_netwinder())
 212                return -ENODEV;
 213
 214        printk (KERN_INFO "NetWinder Button Driver Version %s (C) Alex Holden "
 215                        "<alex@linuxhacker.org> 1998.\n", VERSION);
 216
 217        if (misc_register (&button_misc_device)) {
 218                printk (KERN_WARNING "nwbutton: Couldn't register device 10, "
 219                                "%d.\n", BUTTON_MINOR);
 220                return -EBUSY;
 221        }
 222
 223        if (request_irq (IRQ_NETWINDER_BUTTON, button_handler, IRQF_DISABLED,
 224                        "nwbutton", NULL)) {
 225                printk (KERN_WARNING "nwbutton: IRQ %d is not free.\n",
 226                                IRQ_NETWINDER_BUTTON);
 227                misc_deregister (&button_misc_device);
 228                return -EIO;
 229        }
 230        return 0;
 231}
 232
 233static void __exit nwbutton_exit (void) 
 234{
 235        free_irq (IRQ_NETWINDER_BUTTON, NULL);
 236        misc_deregister (&button_misc_device);
 237}
 238
 239
 240MODULE_AUTHOR("Alex Holden");
 241MODULE_LICENSE("GPL");
 242
 243module_init(nwbutton_init);
 244module_exit(nwbutton_exit);
 245
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