drivers/char/nwbutton.c

   1 /*
   2  *      NetWinder Button Driver-
   3  *      Copyright (C) Alex Holden <alex@linuxhacker.org> 1998, 1999.
   4  *
   5  */
   6
   7 #include <linux/config.h>
   8 #include <linux/module.h>
   9 #include <linux/kernel.h>
  10 #include <linux/sched.h>
  11 #include <linux/interrupt.h>
  12 #include <linux/time.h>
  13 #include <linux/timer.h>
  14 #include <linux/fs.h>
  15 #include <linux/miscdevice.h>
  16 #include <linux/string.h>
  17 #include <linux/errno.h>
  18 #include <linux/init.h>
  19
  20 #include <asm/uaccess.h>
  21 #include <asm/irq.h>
  22 #include <asm/mach-types.h>
  23
  24 #define __NWBUTTON_C            /* Tell the header file who we are */
  25 #include "nwbutton.h"
  26
  27 static int button_press_count;          /* The count of button presses */
  28 static struct timer_list button_timer;  /* Times for the end of a sequence */
  29 static DECLARE_WAIT_QUEUE_HEAD(button_wait_queue); /* Used for blocking read */
  30 static char button_output_buffer[32];   /* Stores data to write out of device */
  31 static int bcount;                      /* The number of bytes in the buffer */
  32 static int bdelay = BUTTON_DELAY;       /* The delay, in jiffies */
  33 static struct button_callback button_callback_list[32]; /* The callback list */
  34 static int callback_count;              /* The number of callbacks registered */
  35 static int reboot_count = NUM_PRESSES_REBOOT; /* Number of presses to reboot */
  36
  37 /*
  38  * This function is called by other drivers to register a callback function
  39  * to be called when a particular number of button presses occurs.
  40  * The callback list is a static array of 32 entries (I somehow doubt many
  41  * people are ever going to want to register more than 32 different actions
  42  * to be performed by the kernel on different numbers of button presses ;).
  43  * However, if an attempt to register a 33rd entry (perhaps a stuck loop
  44  * somewhere registering the same entry over and over?) it will fail to
  45  * do so and return -ENOMEM. If an attempt is made to register a null pointer,
  46  * it will fail to do so and return -EINVAL.
  47  * Because callbacks can be unregistered at random the list can become
  48  * fragmented, so we need to search through the list until we find the first
  49  * free entry.
  50  *
  51  * FIXME: Has anyone spotted any locking functions int his code recently ??
  52  */
  53
  54 int button_add_callback (void (*callback) (void), int count)
  55 {
  56         int lp = 0;
  57         if (callback_count == 32) {
  58                 return -ENOMEM;
  59         }
  60         if (!callback) {
  61                 return -EINVAL;
  62         }
  63         callback_count++;
  64         for (; (button_callback_list [lp].callback); lp++);
  65         button_callback_list [lp].callback = callback;
  66         button_callback_list [lp].count = count;
  67         return 0;
  68 }
  69
  70 /*
  71  * This function is called by other drivers to deregister a callback function.
  72  * If you attempt to unregister a callback which does not exist, it will fail
  73  * with -EINVAL. If there is more than one entry with the same address,
  74  * because it searches the list from end to beginning, it will unregister the
  75  * last one to be registered first (FILO- First In Last Out).
  76  * Note that this is not neccessarily true if the entries are not submitted
  77  * at the same time, because another driver could have unregistered a callback
  78  * between the submissions creating a gap earlier in the list, which would
  79  * be filled first at submission time.
  80  */
  81
  82 int button_del_callback (void (*callback) (void))
  83 {
  84         int lp = 31;
  85         if (!callback) {
  86                 return -EINVAL;
  87         }
  88         while (lp >= 0) {
  89                 if ((button_callback_list [lp].callback) == callback) {
  90                         button_callback_list [lp].callback = NULL;
  91                         button_callback_list [lp].count = 0;
  92                         callback_count--;
  93                         return 0;
  94                 };
  95                 lp--;
  96         };
  97         return -EINVAL;
  98 }
  99
 100 /*
 101  * This function is called by button_sequence_finished to search through the
 102  * list of callback functions, and call any of them whose count argument
 103  * matches the current count of button presses. It starts at the beginning
 104  * of the list and works up to the end. It will refuse to follow a null
 105  * pointer (which should never happen anyway).
 106  */
 107
 108 static void button_consume_callbacks (int bpcount)
 109 {
 110         int lp = 0;
 111         for (; lp <= 31; lp++) {
 112                 if ((button_callback_list [lp].count) == bpcount) {
 113                         if (button_callback_list [lp].callback) {
 114                                 button_callback_list[lp].callback();
 115                         }
 116                 }
 117         }
 118 }
 119
 120 /*
 121  * This function is called when the button_timer times out.
 122  * ie. When you don't press the button for bdelay jiffies, this is taken to
 123  * mean you have ended the sequence of key presses, and this function is
 124  * called to wind things up (write the press_count out to /dev/button, call
 125  * any matching registered function callbacks, initiate reboot, etc.).
 126  */
 127
 128 static void button_sequence_finished (unsigned long parameters)
 129 {
 130 #ifdef CONFIG_NWBUTTON_REBOOT           /* Reboot using button is enabled */
 131         if (button_press_count == reboot_count) {
 132                 kill_proc (1, SIGINT, 1);       /* Ask init to reboot us */
 133         }
 134 #endif /* CONFIG_NWBUTTON_REBOOT */
 135         button_consume_callbacks (button_press_count);
 136         bcount = sprintf (button_output_buffer, "%d\n", button_press_count);
 137         button_press_count = 0;         /* Reset the button press counter */
 138         wake_up_interruptible (&button_wait_queue);
 139 }
 140
 141 /*
 142  *  This handler is called when the orange button is pressed (GPIO 10 of the
 143  *  SuperIO chip, which maps to logical IRQ 26). If the press_count is 0,
 144  *  this is the first press, so it starts a timer and increments the counter.
 145  *  If it is higher than 0, it deletes the old timer, starts a new one, and
 146  *  increments the counter.
 147  */
 148
 149 static irqreturn_t button_handler (int irq, void *dev_id, struct pt_regs *regs)
 150 {
 151         if (button_press_count) {
 152                 del_timer (&button_timer);
 153         }
 154         button_press_count++;
 155         init_timer (&button_timer);
 156         button_timer.function = button_sequence_finished;
 157         button_timer.expires = (jiffies + bdelay);
 158         add_timer (&button_timer);
 159
 160         return IRQ_HANDLED;
 161 }
 162
 163 /*
 164  * This function is called when a user space program attempts to read
 165  * /dev/nwbutton. It puts the device to sleep on the wait queue until
 166  * button_sequence_finished writes some data to the buffer and flushes
 167  * the queue, at which point it writes the data out to the device and
 168  * returns the number of characters it has written. This function is
 169  * reentrant, so that many processes can be attempting to read from the
 170  * device at any one time.
 171  */
 172
 173 static int button_read (struct file *filp, char __user *buffer,
 174                         size_t count, loff_t *ppos)
 175 {
 176         interruptible_sleep_on (&button_wait_queue);
 177         return (copy_to_user (buffer, &button_output_buffer, bcount))
 178                  ? -EFAULT : bcount;
 179 }
 180
 181 /*
 182  * This structure is the file operations structure, which specifies what
 183  * callbacks functions the kernel should call when a user mode process
 184  * attempts to perform these operations on the device.
 185  */
 186
 187 static struct file_operations button_fops = {
 188         .owner          = THIS_MODULE,
 189         .read           = button_read,
 190 };
 191
 192 /*
 193  * This structure is the misc device structure, which specifies the minor
 194  * device number (158 in this case), the name of the device (for /proc/misc),
 195  * and the address of the above file operations structure.
 196  */
 197
 198 static struct miscdevice button_misc_device = {
 199         BUTTON_MINOR,
 200         "nwbutton",
 201         &button_fops,
 202 };
 203
 204 /*
 205  * This function is called to initialise the driver, either from misc.c at
 206  * bootup if the driver is compiled into the kernel, or from init_module
 207  * below at module insert time. It attempts to register the device node
 208  * and the IRQ and fails with a warning message if either fails, though
 209  * neither ever should because the device number and IRQ are unique to
 210  * this driver.
 211  */
 212
 213 static int __init nwbutton_init(void)
 214 {
 215         if (!machine_is_netwinder())
 216                 return -ENODEV;
 217
 218         printk (KERN_INFO "NetWinder Button Driver Version %s (C) Alex Holden "
 219                         "<alex@linuxhacker.org> 1998.\n", VERSION);
 220
 221         if (misc_register (&button_misc_device)) {
 222                 printk (KERN_WARNING "nwbutton: Couldn't register device 10, "
 223                                 "%d.\n", BUTTON_MINOR);
 224                 return -EBUSY;
 225         }
 226
 227         if (request_irq (IRQ_NETWINDER_BUTTON, button_handler, SA_INTERRUPT,
 228                         "nwbutton", NULL)) {
 229                 printk (KERN_WARNING "nwbutton: IRQ %d is not free.\n",
 230                                 IRQ_NETWINDER_BUTTON);
 231                 misc_deregister (&button_misc_device);
 232                 return -EIO;
 233         }
 234         return 0;
 235 }
 236
 237 static void __exit nwbutton_exit (void)
 238 {
 239         free_irq (IRQ_NETWINDER_BUTTON, NULL);
 240         misc_deregister (&button_misc_device);
 241 }
 242
 243
 244 MODULE_AUTHOR("Alex Holden");
 245 MODULE_LICENSE("GPL");
 246
 247 module_init(nwbutton_init);
 248 module_exit(nwbutton_exit);