drivers/char/nwbutton.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *      NetWinder Button Driver-
   4  *      Copyright (C) Alex Holden <alex@linuxhacker.org> 1998, 1999.
   5  *
   6  */
   7
   8 #include <linux/module.h>
   9 #include <linux/kernel.h>
  10 #include <linux/sched/signal.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 <linux/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 void button_sequence_finished(struct timer_list *unused);
  28
  29 static int button_press_count;          /* The count of button presses */
  30 /* Times for the end of a sequence */
  31 static DEFINE_TIMER(button_timer, button_sequence_finished);
  32 static DECLARE_WAIT_QUEUE_HEAD(button_wait_queue); /* Used for blocking read */
  33 static char button_output_buffer[32];   /* Stores data to write out of device */
  34 static int bcount;                      /* The number of bytes in the buffer */
  35 static int bdelay = BUTTON_DELAY;       /* The delay, in jiffies */
  36 static struct button_callback button_callback_list[32]; /* The callback list */
  37 static int callback_count;              /* The number of callbacks registered */
  38 static int reboot_count = NUM_PRESSES_REBOOT; /* Number of presses to reboot */
  39
  40 /*
  41  * This function is called by other drivers to register a callback function
  42  * to be called when a particular number of button presses occurs.
  43  * The callback list is a static array of 32 entries (I somehow doubt many
  44  * people are ever going to want to register more than 32 different actions
  45  * to be performed by the kernel on different numbers of button presses ;).
  46  * However, if an attempt to register a 33rd entry (perhaps a stuck loop
  47  * somewhere registering the same entry over and over?) it will fail to
  48  * do so and return -ENOMEM. If an attempt is made to register a null pointer,
  49  * it will fail to do so and return -EINVAL.
  50  * Because callbacks can be unregistered at random the list can become
  51  * fragmented, so we need to search through the list until we find the first
  52  * free entry.
  53  *
  54  * FIXME: Has anyone spotted any locking functions int his code recently ??
  55  */
  56
  57 int button_add_callback (void (*callback) (void), int count)
  58 {
  59         int lp = 0;
  60         if (callback_count == 32) {
  61                 return -ENOMEM;
  62         }
  63         if (!callback) {
  64                 return -EINVAL;
  65         }
  66         callback_count++;
  67         for (; (button_callback_list [lp].callback); lp++);
  68         button_callback_list [lp].callback = callback;
  69         button_callback_list [lp].count = count;
  70         return 0;
  71 }
  72
  73 /*
  74  * This function is called by other drivers to deregister a callback function.
  75  * If you attempt to unregister a callback which does not exist, it will fail
  76  * with -EINVAL. If there is more than one entry with the same address,
  77  * because it searches the list from end to beginning, it will unregister the
  78  * last one to be registered first (FILO- First In Last Out).
  79  * Note that this is not necessarily true if the entries are not submitted
  80  * at the same time, because another driver could have unregistered a callback
  81  * between the submissions creating a gap earlier in the list, which would
  82  * be filled first at submission time.
  83  */
  84
  85 int button_del_callback (void (*callback) (void))
  86 {
  87         int lp = 31;
  88         if (!callback) {
  89                 return -EINVAL;
  90         }
  91         while (lp >= 0) {
  92                 if ((button_callback_list [lp].callback) == callback) {
  93                         button_callback_list [lp].callback = NULL;
  94                         button_callback_list [lp].count = 0;
  95                         callback_count--;
  96                         return 0;
  97                 }
  98                 lp--;
  99         }
 100         return -EINVAL;
 101 }
 102
 103 /*
 104  * This function is called by button_sequence_finished to search through the
 105  * list of callback functions, and call any of them whose count argument
 106  * matches the current count of button presses. It starts at the beginning
 107  * of the list and works up to the end. It will refuse to follow a null
 108  * pointer (which should never happen anyway).
 109  */
 110
 111 static void button_consume_callbacks (int bpcount)
 112 {
 113         int lp = 0;
 114         for (; lp <= 31; lp++) {
 115                 if ((button_callback_list [lp].count) == bpcount) {
 116                         if (button_callback_list [lp].callback) {
 117                                 button_callback_list[lp].callback();
 118                         }
 119                 }
 120         }
 121 }
 122
 123 /*
 124  * This function is called when the button_timer times out.
 125  * ie. When you don't press the button for bdelay jiffies, this is taken to
 126  * mean you have ended the sequence of key presses, and this function is
 127  * called to wind things up (write the press_count out to /dev/button, call
 128  * any matching registered function callbacks, initiate reboot, etc.).
 129  */
 130
 131 static void button_sequence_finished(struct timer_list *unused)
 132 {
 133         if (IS_ENABLED(CONFIG_NWBUTTON_REBOOT) &&
 134             button_press_count == reboot_count)
 135                 kill_cad_pid(SIGINT, 1);        /* Ask init to reboot us */
 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
 150 static 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
 168 static int button_read (struct file *filp, char __user *buffer,
 169                         size_t count, loff_t *ppos)
 170 {
 171         DEFINE_WAIT(wait);
 172         prepare_to_wait(&button_wait_queue, &wait, TASK_INTERRUPTIBLE);
 173         schedule();
 174         finish_wait(&button_wait_queue, &wait);
 175         return (copy_to_user (buffer, &button_output_buffer, bcount))
 176                  ? -EFAULT : bcount;
 177 }
 178
 179 /*
 180  * This structure is the file operations structure, which specifies what
 181  * callbacks functions the kernel should call when a user mode process
 182  * attempts to perform these operations on the device.
 183  */
 184
 185 static const struct file_operations button_fops = {
 186         .owner          = THIS_MODULE,
 187         .read           = button_read,
 188         .llseek         = noop_llseek,
 189 };
 190
 191 /*
 192  * This structure is the misc device structure, which specifies the minor
 193  * device number (158 in this case), the name of the device (for /proc/misc),
 194  * and the address of the above file operations structure.
 195  */
 196
 197 static struct miscdevice button_misc_device = {
 198         BUTTON_MINOR,
 199         "nwbutton",
 200         &button_fops,
 201 };
 202
 203 /*
 204  * This function is called to initialise the driver, either from misc.c at
 205  * bootup if the driver is compiled into the kernel, or from init_module
 206  * below at module insert time. It attempts to register the device node
 207  * and the IRQ and fails with a warning message if either fails, though
 208  * neither ever should because the device number and IRQ are unique to
 209  * this driver.
 210  */
 211
 212 static int __init nwbutton_init(void)
 213 {
 214         if (!machine_is_netwinder())
 215                 return -ENODEV;
 216
 217         printk (KERN_INFO "NetWinder Button Driver Version %s (C) Alex Holden "
 218                         "<alex@linuxhacker.org> 1998.\n", VERSION);
 219
 220         if (misc_register (&button_misc_device)) {
 221                 printk (KERN_WARNING "nwbutton: Couldn't register device 10, "
 222                                 "%d.\n", BUTTON_MINOR);
 223                 return -EBUSY;
 224         }
 225
 226         if (request_irq (IRQ_NETWINDER_BUTTON, button_handler, 0,
 227                         "nwbutton", NULL)) {
 228                 printk (KERN_WARNING "nwbutton: IRQ %d is not free.\n",
 229                                 IRQ_NETWINDER_BUTTON);
 230                 misc_deregister (&button_misc_device);
 231                 return -EIO;
 232         }
 233         return 0;
 234 }
 235
 236 static void __exit nwbutton_exit (void)
 237 {
 238         free_irq (IRQ_NETWINDER_BUTTON, NULL);
 239         misc_deregister (&button_misc_device);
 240 }
 241
 242
 243 MODULE_AUTHOR("Alex Holden");
 244 MODULE_LICENSE("GPL");
 245
 246 module_init(nwbutton_init);
 247 module_exit(nwbutton_exit);