d185247ba1aa46b3b18bfb10792a95d17b4b28b2
[linux-3.10.git] / drivers / tty / serial / kgdb_nmi.c
1 /*
2  * KGDB NMI serial console
3  *
4  * Copyright 2010 Google, Inc.
5  *                Arve Hjønnevåg <arve@android.com>
6  *                Colin Cross <ccross@android.com>
7  * Copyright 2012 Linaro Ltd.
8  *                Anton Vorontsov <anton.vorontsov@linaro.org>
9  *
10  * This program is free software; you can redistribute it and/or modify it
11  * under the terms of the GNU General Public License version 2 as published
12  * by the Free Software Foundation.
13  */
14
15 #include <linux/kernel.h>
16 #include <linux/module.h>
17 #include <linux/compiler.h>
18 #include <linux/init.h>
19 #include <linux/slab.h>
20 #include <linux/errno.h>
21 #include <linux/atomic.h>
22 #include <linux/console.h>
23 #include <linux/tty.h>
24 #include <linux/tty_driver.h>
25 #include <linux/tty_flip.h>
26 #include <linux/interrupt.h>
27 #include <linux/hrtimer.h>
28 #include <linux/tick.h>
29 #include <linux/kfifo.h>
30 #include <linux/kgdb.h>
31 #include <linux/kdb.h>
32
33 static int kgdb_nmi_knock = 1;
34 module_param_named(knock, kgdb_nmi_knock, int, 0600);
35 MODULE_PARM_DESC(knock, "if set to 1 (default), the special '$3#33' command " \
36                         "must be used to enter the debugger; when set to 0, " \
37                         "hitting return key is enough to enter the debugger; " \
38                         "when set to -1, the debugger is entered immediately " \
39                         "upon NMI");
40
41 static char *kgdb_nmi_magic = "$3#33";
42 module_param_named(magic, kgdb_nmi_magic, charp, 0600);
43 MODULE_PARM_DESC(magic, "magic sequence to enter NMI debugger (default $3#33)");
44
45 static bool kgdb_nmi_tty_enabled;
46
47 static void kgdb_nmi_console_write(struct console *co, const char *s, uint c)
48 {
49         int i;
50
51         if (!kgdb_nmi_tty_enabled || atomic_read(&kgdb_active) >= 0)
52                 return;
53
54         for (i = 0; i < c; i++)
55                 dbg_io_ops->write_char(s[i]);
56 }
57
58 static struct tty_driver *kgdb_nmi_tty_driver;
59
60 static struct tty_driver *kgdb_nmi_console_device(struct console *co, int *idx)
61 {
62         *idx = co->index;
63         return kgdb_nmi_tty_driver;
64 }
65
66 static struct console kgdb_nmi_console = {
67         .name   = "ttyNMI",
68         .write  = kgdb_nmi_console_write,
69         .device = kgdb_nmi_console_device,
70         .flags  = CON_PRINTBUFFER | CON_ANYTIME | CON_ENABLED,
71         .index  = -1,
72 };
73
74 /*
75  * This is usually the maximum rate on debug ports. We make fifo large enough
76  * to make copy-pasting to the terminal usable.
77  */
78 #define KGDB_NMI_BAUD           115200
79 #define KGDB_NMI_FIFO_SIZE      roundup_pow_of_two(KGDB_NMI_BAUD / 8 / HZ)
80
81 struct kgdb_nmi_tty_priv {
82         struct tty_port port;
83         struct tasklet_struct tlet;
84         STRUCT_KFIFO(char, KGDB_NMI_FIFO_SIZE) fifo;
85 };
86
87 static struct kgdb_nmi_tty_priv *kgdb_nmi_port_to_priv(struct tty_port *port)
88 {
89         return container_of(port, struct kgdb_nmi_tty_priv, port);
90 }
91
92 /*
93  * Our debugging console is polled in a tasklet, so we'll check for input
94  * every tick. In HZ-less mode, we should program the next tick.  We have
95  * to use the lowlevel stuff as no locks should be grabbed.
96  */
97 #ifdef CONFIG_HIGH_RES_TIMERS
98 static void kgdb_tty_poke(void)
99 {
100         tick_program_event(ktime_get(), 0);
101 }
102 #else
103 static inline void kgdb_tty_poke(void) {}
104 #endif
105
106 static struct tty_port *kgdb_nmi_port;
107
108 static void kgdb_tty_recv(int ch)
109 {
110         struct kgdb_nmi_tty_priv *priv;
111         char c = ch;
112
113         if (!kgdb_nmi_port || ch < 0)
114                 return;
115         /*
116          * Can't use port->tty->driver_data as tty might be not there. Tasklet
117          * will check for tty and will get the ref, but here we don't have to
118          * do that, and actually, we can't: we're in NMI context, no locks are
119          * possible.
120          */
121         priv = kgdb_nmi_port_to_priv(kgdb_nmi_port);
122         kfifo_in(&priv->fifo, &c, 1);
123         kgdb_tty_poke();
124 }
125
126 static int kgdb_nmi_poll_one_knock(void)
127 {
128         static int n;
129         int c = -1;
130         const char *magic = kgdb_nmi_magic;
131         size_t m = strlen(magic);
132         bool printch = 0;
133
134         c = dbg_io_ops->read_char();
135         if (c == NO_POLL_CHAR)
136                 return c;
137
138         if (!kgdb_nmi_knock && (c == '\r' || c == '\n')) {
139                 return 1;
140         } else if (c == magic[n]) {
141                 n = (n + 1) % m;
142                 if (!n)
143                         return 1;
144                 printch = 1;
145         } else {
146                 n = 0;
147         }
148
149         if (kgdb_nmi_tty_enabled) {
150                 kgdb_tty_recv(c);
151                 return 0;
152         }
153
154         if (printch) {
155                 kdb_printf("%c", c);
156                 return 0;
157         }
158
159         kdb_printf("\r%s %s to enter the debugger> %*s",
160                    kgdb_nmi_knock ? "Type" : "Hit",
161                    kgdb_nmi_knock ? magic  : "<return>", (int)m, "");
162         while (m--)
163                 kdb_printf("\b");
164         return 0;
165 }
166
167 /**
168  * kgdb_nmi_poll_knock - Check if it is time to enter the debugger
169  *
170  * "Serial ports are often noisy, especially when muxed over another port (we
171  * often use serial over the headset connector). Noise on the async command
172  * line just causes characters that are ignored, on a command line that blocked
173  * execution noise would be catastrophic." -- Colin Cross
174  *
175  * So, this function implements KGDB/KDB knocking on the serial line: we won't
176  * enter the debugger until we receive a known magic phrase (which is actually
177  * "$3#33", known as "escape to KDB" command. There is also a relaxed variant
178  * of knocking, i.e. just pressing the return key is enough to enter the
179  * debugger. And if knocking is disabled, the function always returns 1.
180  */
181 bool kgdb_nmi_poll_knock(void)
182 {
183         if (kgdb_nmi_knock < 0)
184                 return 1;
185
186         while (1) {
187                 int ret;
188
189                 ret = kgdb_nmi_poll_one_knock();
190                 if (ret == NO_POLL_CHAR)
191                         return 0;
192                 else if (ret == 1)
193                         break;
194         }
195         return 1;
196 }
197
198 /*
199  * The tasklet is cheap, it does not cause wakeups when reschedules itself,
200  * instead it waits for the next tick.
201  */
202 static void kgdb_nmi_tty_receiver(unsigned long data)
203 {
204         struct kgdb_nmi_tty_priv *priv = (void *)data;
205         struct tty_struct *tty;
206         char ch;
207
208         tasklet_schedule(&priv->tlet);
209
210         if (likely(!kgdb_nmi_tty_enabled || !kfifo_len(&priv->fifo)))
211                 return;
212
213         /* Port is there, but tty might be hung up, check. */
214         tty = tty_port_tty_get(kgdb_nmi_port);
215         if (!tty)
216                 return;
217
218         while (kfifo_out(&priv->fifo, &ch, 1))
219                 tty_insert_flip_char(priv->port.tty, ch, TTY_NORMAL);
220         tty_flip_buffer_push(priv->port.tty);
221
222         tty_kref_put(tty);
223 }
224
225 static int kgdb_nmi_tty_activate(struct tty_port *port, struct tty_struct *tty)
226 {
227         struct kgdb_nmi_tty_priv *priv = tty->driver_data;
228
229         kgdb_nmi_port = port;
230         tasklet_schedule(&priv->tlet);
231         return 0;
232 }
233
234 static void kgdb_nmi_tty_shutdown(struct tty_port *port)
235 {
236         struct kgdb_nmi_tty_priv *priv = port->tty->driver_data;
237
238         tasklet_kill(&priv->tlet);
239         kgdb_nmi_port = NULL;
240 }
241
242 static const struct tty_port_operations kgdb_nmi_tty_port_ops = {
243         .activate       = kgdb_nmi_tty_activate,
244         .shutdown       = kgdb_nmi_tty_shutdown,
245 };
246
247 static int kgdb_nmi_tty_install(struct tty_driver *drv, struct tty_struct *tty)
248 {
249         struct kgdb_nmi_tty_priv *priv;
250         int ret;
251
252         priv = kzalloc(sizeof(*priv), GFP_KERNEL);
253         if (!priv)
254                 return -ENOMEM;
255
256         INIT_KFIFO(priv->fifo);
257         tasklet_init(&priv->tlet, kgdb_nmi_tty_receiver, (unsigned long)priv);
258         tty_port_init(&priv->port);
259         priv->port.ops = &kgdb_nmi_tty_port_ops;
260         tty->driver_data = priv;
261
262         ret = tty_port_install(&priv->port, drv, tty);
263         if (ret) {
264                 pr_err("%s: can't install tty port: %d\n", __func__, ret);
265                 goto err;
266         }
267         return 0;
268 err:
269         kfree(priv);
270         return ret;
271 }
272
273 static void kgdb_nmi_tty_cleanup(struct tty_struct *tty)
274 {
275         struct kgdb_nmi_tty_priv *priv = tty->driver_data;
276
277         tty->driver_data = NULL;
278         kfree(priv);
279 }
280
281 static int kgdb_nmi_tty_open(struct tty_struct *tty, struct file *file)
282 {
283         struct kgdb_nmi_tty_priv *priv = tty->driver_data;
284
285         return tty_port_open(&priv->port, tty, file);
286 }
287
288 static void kgdb_nmi_tty_close(struct tty_struct *tty, struct file *file)
289 {
290         struct kgdb_nmi_tty_priv *priv = tty->driver_data;
291
292         tty_port_close(&priv->port, tty, file);
293 }
294
295 static void kgdb_nmi_tty_hangup(struct tty_struct *tty)
296 {
297         struct kgdb_nmi_tty_priv *priv = tty->driver_data;
298
299         tty_port_hangup(&priv->port);
300 }
301
302 static int kgdb_nmi_tty_write_room(struct tty_struct *tty)
303 {
304         /* Actually, we can handle any amount as we use polled writes. */
305         return 2048;
306 }
307
308 static int kgdb_nmi_tty_write(struct tty_struct *tty, const unchar *buf, int c)
309 {
310         int i;
311
312         for (i = 0; i < c; i++)
313                 dbg_io_ops->write_char(buf[i]);
314         return c;
315 }
316
317 static const struct tty_operations kgdb_nmi_tty_ops = {
318         .open           = kgdb_nmi_tty_open,
319         .close          = kgdb_nmi_tty_close,
320         .install        = kgdb_nmi_tty_install,
321         .cleanup        = kgdb_nmi_tty_cleanup,
322         .hangup         = kgdb_nmi_tty_hangup,
323         .write_room     = kgdb_nmi_tty_write_room,
324         .write          = kgdb_nmi_tty_write,
325 };
326
327 static int kgdb_nmi_enable_console(int argc, const char *argv[])
328 {
329         kgdb_nmi_tty_enabled = !(argc == 1 && !strcmp(argv[1], "off"));
330         return 0;
331 }
332
333 int kgdb_register_nmi_console(void)
334 {
335         int ret;
336
337         if (!arch_kgdb_ops.enable_nmi)
338                 return 0;
339
340         kgdb_nmi_tty_driver = alloc_tty_driver(1);
341         if (!kgdb_nmi_tty_driver) {
342                 pr_err("%s: cannot allocate tty\n", __func__);
343                 return -ENOMEM;
344         }
345         kgdb_nmi_tty_driver->driver_name        = "ttyNMI";
346         kgdb_nmi_tty_driver->name               = "ttyNMI";
347         kgdb_nmi_tty_driver->num                = 1;
348         kgdb_nmi_tty_driver->type               = TTY_DRIVER_TYPE_SERIAL;
349         kgdb_nmi_tty_driver->subtype            = SERIAL_TYPE_NORMAL;
350         kgdb_nmi_tty_driver->flags              = TTY_DRIVER_REAL_RAW;
351         kgdb_nmi_tty_driver->init_termios       = tty_std_termios;
352         tty_termios_encode_baud_rate(&kgdb_nmi_tty_driver->init_termios,
353                                      KGDB_NMI_BAUD, KGDB_NMI_BAUD);
354         tty_set_operations(kgdb_nmi_tty_driver, &kgdb_nmi_tty_ops);
355
356         ret = tty_register_driver(kgdb_nmi_tty_driver);
357         if (ret) {
358                 pr_err("%s: can't register tty driver: %d\n", __func__, ret);
359                 goto err_drv_reg;
360         }
361
362         ret = kdb_register("nmi_console", kgdb_nmi_enable_console, "[off]",
363                            "switch to Linux NMI console", 0);
364         if (ret) {
365                 pr_err("%s: can't register kdb command: %d\n", __func__, ret);
366                 goto err_kdb_reg;
367         }
368
369         register_console(&kgdb_nmi_console);
370         arch_kgdb_ops.enable_nmi(1);
371
372         return 0;
373 err_kdb_reg:
374         tty_unregister_driver(kgdb_nmi_tty_driver);
375 err_drv_reg:
376         put_tty_driver(kgdb_nmi_tty_driver);
377         return ret;
378 }
379 EXPORT_SYMBOL_GPL(kgdb_register_nmi_console);
380
381 int kgdb_unregister_nmi_console(void)
382 {
383         int ret;
384
385         if (!arch_kgdb_ops.enable_nmi)
386                 return 0;
387         arch_kgdb_ops.enable_nmi(0);
388
389         kdb_unregister("nmi_console");
390
391         ret = unregister_console(&kgdb_nmi_console);
392         if (ret)
393                 return ret;
394
395         ret = tty_unregister_driver(kgdb_nmi_tty_driver);
396         if (ret)
397                 return ret;
398         put_tty_driver(kgdb_nmi_tty_driver);
399
400         return 0;
401 }
402 EXPORT_SYMBOL_GPL(kgdb_unregister_nmi_console);