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 
button_add_callback(void (* callback)(void),int count)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 
button_del_callback(void (* callback)(void))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 
button_consume_callbacks(int bpcount)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 
button_sequence_finished(struct timer_list * unused)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 
button_handler(int irq,void * dev_id)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 
button_read(struct file * filp,char __user * buffer,size_t count,loff_t * ppos)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 
nwbutton_init(void)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 
nwbutton_exit(void)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);
248