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/module.h>
   8 #include <linux/kernel.h>
   9 #include <linux/sched/signal.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 <linux/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
  26 static void button_sequence_finished (unsigned long parameters);
  27
  28 static int button_press_count;          /* The count of button presses */
  29 /* Times for the end of a sequence */
  30 static DEFINE_TIMER(button_timer, button_sequence_finished);
  31 static DECLARE_WAIT_QUEUE_HEAD(button_wait_queue); /* Used for blocking read */
  32 static char button_output_buffer[32];   /* Stores data to write out of device */
  33 static int bcount;                      /* The number of bytes in the buffer */
  34 static int bdelay = BUTTON_DELAY;       /* The delay, in jiffies */
  35 static struct button_callback button_callback_list[32]; /* The callback list */
  36 static int callback_count;              /* The number of callbacks registered */
  37 static 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
  56 int 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
  84 int 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
 110 static 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
 130 static void button_sequence_finished (unsigned long parameters)
 131 {
 132         if (IS_ENABLED(CONFIG_NWBUTTON_REBOOT) &&
 133             button_press_count == reboot_count)
 134                 kill_cad_pid(SIGINT, 1);        /* Ask init to reboot us */
 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)
 150 {
 151         button_press_count++;
 152         mod_timer(&button_timer, jiffies + bdelay);
 153
 154         return IRQ_HANDLED;
 155 }
 156
 157 /*
 158  * This function is called when a user space program attempts to read
 159  * /dev/nwbutton. It puts the device to sleep on the wait queue until
 160  * button_sequence_finished writes some data to the buffer and flushes
 161  * the queue, at which point it writes the data out to the device and
 162  * returns the number of characters it has written. This function is
 163  * reentrant, so that many processes can be attempting to read from the
 164  * device at any one time.
 165  */
 166
 167 static int button_read (struct file *filp, char __user *buffer,
 168                         size_t count, loff_t *ppos)
 169 {
 170         DEFINE_WAIT(wait);
 171         prepare_to_wait(&button_wait_queue, &wait, TASK_INTERRUPTIBLE);
 172         schedule();
 173         finish_wait(&button_wait_queue, &wait);
 174         return (copy_to_user (buffer, &button_output_buffer, bcount))
 175                  ? -EFAULT : bcount;
 176 }
 177
 178 /*
 179  * This structure is the file operations structure, which specifies what
 180  * callbacks functions the kernel should call when a user mode process
 181  * attempts to perform these operations on the device.
 182  */
 183
 184 static const struct file_operations button_fops = {
 185         .owner          = THIS_MODULE,
 186         .read           = button_read,
 187         .llseek         = noop_llseek,
 188 };
 189
 190 /*
 191  * This structure is the misc device structure, which specifies the minor
 192  * device number (158 in this case), the name of the device (for /proc/misc),
 193  * and the address of the above file operations structure.
 194  */
 195
 196 static struct miscdevice button_misc_device = {
 197         BUTTON_MINOR,
 198         "nwbutton",
 199         &button_fops,
 200 };
 201
 202 /*
 203  * This function is called to initialise the driver, either from misc.c at
 204  * bootup if the driver is compiled into the kernel, or from init_module
 205  * below at module insert time. It attempts to register the device node
 206  * and the IRQ and fails with a warning message if either fails, though
 207  * neither ever should because the device number and IRQ are unique to
 208  * this driver.
 209  */
 210
 211 static int __init nwbutton_init(void)
 212 {
 213         if (!machine_is_netwinder())
 214                 return -ENODEV;
 215
 216         printk (KERN_INFO "NetWinder Button Driver Version %s (C) Alex Holden "
 217                         "<alex@linuxhacker.org> 1998.\n", VERSION);
 218
 219         if (misc_register (&button_misc_device)) {
 220                 printk (KERN_WARNING "nwbutton: Couldn't register device 10, "
 221                                 "%d.\n", BUTTON_MINOR);
 222                 return -EBUSY;
 223         }
 224
 225         if (request_irq (IRQ_NETWINDER_BUTTON, button_handler, 0,
 226                         "nwbutton", NULL)) {
 227                 printk (KERN_WARNING "nwbutton: IRQ %d is not free.\n",
 228                                 IRQ_NETWINDER_BUTTON);
 229                 misc_deregister (&button_misc_device);
 230                 return -EIO;
 231         }
 232         return 0;
 233 }
 234
 235 static void __exit nwbutton_exit (void)
 236 {
 237         free_irq (IRQ_NETWINDER_BUTTON, NULL);
 238         misc_deregister (&button_misc_device);
 239 }
 240
 241
 242 MODULE_AUTHOR("Alex Holden");
 243 MODULE_LICENSE("GPL");
 244
 245 module_init(nwbutton_init);
 246 module_exit(nwbutton_exit);