1// SPDX-License-Identifier: GPL-2.0
2/*
3 * KGDB NMI serial console
4 *
5 * Copyright 2010 Google, Inc.
6 * Arve Hjønnevåg <arve@android.com>
7 * Colin Cross <ccross@android.com>
8 * Copyright 2012 Linaro Ltd.
9 * Anton Vorontsov <anton.vorontsov@linaro.org>
10 */
11
12#include <linux/kernel.h>
13#include <linux/module.h>
14#include <linux/compiler.h>
15#include <linux/slab.h>
16#include <linux/errno.h>
17#include <linux/atomic.h>
18#include <linux/console.h>
19#include <linux/tty.h>
20#include <linux/tty_driver.h>
21#include <linux/tty_flip.h>
22#include <linux/serial_core.h>
23#include <linux/interrupt.h>
24#include <linux/hrtimer.h>
25#include <linux/tick.h>
26#include <linux/kfifo.h>
27#include <linux/kgdb.h>
28#include <linux/kdb.h>
29
30static int kgdb_nmi_knock = 1;
31module_param_named(knock, kgdb_nmi_knock, int, 0600);
32MODULE_PARM_DESC(knock, "if set to 1 (default), the special '$3#33' command " \
33 "must be used to enter the debugger; when set to 0, " \
34 "hitting return key is enough to enter the debugger; " \
35 "when set to -1, the debugger is entered immediately " \
36 "upon NMI");
37
38static char *kgdb_nmi_magic = "$3#33";
39module_param_named(magic, kgdb_nmi_magic, charp, 0600);
40MODULE_PARM_DESC(magic, "magic sequence to enter NMI debugger (default $3#33)");
41
42static atomic_t kgdb_nmi_num_readers = ATOMIC_INIT(0);
43
44static int kgdb_nmi_console_setup(struct console *co, char *options)
45{
46 arch_kgdb_ops.enable_nmi(1);
47
48 /* The NMI console uses the dbg_io_ops to issue console messages. To
49 * avoid duplicate messages during kdb sessions we must inform kdb's
50 * I/O utilities that messages sent to the console will automatically
51 * be displayed on the dbg_io.
52 */
53 dbg_io_ops->cons = co;
54
55 return 0;
56}
57
58static void kgdb_nmi_console_write(struct console *co, const char *s, uint c)
59{
60 int i;
61
62 for (i = 0; i < c; i++)
63 dbg_io_ops->write_char(s[i]);
64}
65
66static struct tty_driver *kgdb_nmi_tty_driver;
67
68static struct tty_driver *kgdb_nmi_console_device(struct console *co, int *idx)
69{
70 *idx = co->index;
71 return kgdb_nmi_tty_driver;
72}
73
74static struct console kgdb_nmi_console = {
75 .name = "ttyNMI",
76 .setup = kgdb_nmi_console_setup,
77 .write = kgdb_nmi_console_write,
78 .device = kgdb_nmi_console_device,
79 .flags = CON_PRINTBUFFER | CON_ANYTIME,
80 .index = -1,
81};
82
83/*
84 * This is usually the maximum rate on debug ports. We make fifo large enough
85 * to make copy-pasting to the terminal usable.
86 */
87#define KGDB_NMI_BAUD 115200
88#define KGDB_NMI_FIFO_SIZE roundup_pow_of_two(KGDB_NMI_BAUD / 8 / HZ)
89
90struct kgdb_nmi_tty_priv {
91 struct tty_port port;
92 struct timer_list timer;
93 STRUCT_KFIFO(char, KGDB_NMI_FIFO_SIZE) fifo;
94};
95
96static struct tty_port *kgdb_nmi_port;
97
98static void kgdb_tty_recv(int ch)
99{
100 struct kgdb_nmi_tty_priv *priv;
101 char c = ch;
102
103 if (!kgdb_nmi_port || ch < 0)
104 return;
105 /*
106 * Can't use port->tty->driver_data as tty might be not there. Timer
107 * will check for tty and will get the ref, but here we don't have to
108 * do that, and actually, we can't: we're in NMI context, no locks are
109 * possible.
110 */
111 priv = container_of(kgdb_nmi_port, struct kgdb_nmi_tty_priv, port);
112 kfifo_in(&priv->fifo, &c, 1);
113}
114
115static int kgdb_nmi_poll_one_knock(void)
116{
117 static int n;
118 int c;
119 const char *magic = kgdb_nmi_magic;
120 size_t m = strlen(magic);
121 bool printch = false;
122
123 c = dbg_io_ops->read_char();
124 if (c == NO_POLL_CHAR)
125 return c;
126
127 if (!kgdb_nmi_knock && (c == '\r' || c == '\n')) {
128 return 1;
129 } else if (c == magic[n]) {
130 n = (n + 1) % m;
131 if (!n)
132 return 1;
133 printch = true;
134 } else {
135 n = 0;
136 }
137
138 if (atomic_read(v: &kgdb_nmi_num_readers)) {
139 kgdb_tty_recv(ch: c);
140 return 0;
141 }
142
143 if (printch) {
144 kdb_printf("%c", c);
145 return 0;
146 }
147
148 kdb_printf("\r%s %s to enter the debugger> %*s",
149 kgdb_nmi_knock ? "Type" : "Hit",
150 kgdb_nmi_knock ? magic : "<return>", (int)m, "");
151 while (m--)
152 kdb_printf("\b");
153 return 0;
154}
155
156/**
157 * kgdb_nmi_poll_knock - Check if it is time to enter the debugger
158 *
159 * "Serial ports are often noisy, especially when muxed over another port (we
160 * often use serial over the headset connector). Noise on the async command
161 * line just causes characters that are ignored, on a command line that blocked
162 * execution noise would be catastrophic." -- Colin Cross
163 *
164 * So, this function implements KGDB/KDB knocking on the serial line: we won't
165 * enter the debugger until we receive a known magic phrase (which is actually
166 * "$3#33", known as "escape to KDB" command. There is also a relaxed variant
167 * of knocking, i.e. just pressing the return key is enough to enter the
168 * debugger. And if knocking is disabled, the function always returns 1.
169 */
170bool kgdb_nmi_poll_knock(void)
171{
172 if (kgdb_nmi_knock < 0)
173 return true;
174
175 while (1) {
176 int ret;
177
178 ret = kgdb_nmi_poll_one_knock();
179 if (ret == NO_POLL_CHAR)
180 return false;
181 else if (ret == 1)
182 break;
183 }
184 return true;
185}
186
187/*
188 * The tasklet is cheap, it does not cause wakeups when reschedules itself,
189 * instead it waits for the next tick.
190 */
191static void kgdb_nmi_tty_receiver(struct timer_list *t)
192{
193 struct kgdb_nmi_tty_priv *priv = from_timer(priv, t, timer);
194 char ch;
195
196 priv->timer.expires = jiffies + (HZ/100);
197 add_timer(timer: &priv->timer);
198
199 if (likely(!atomic_read(&kgdb_nmi_num_readers) ||
200 !kfifo_len(&priv->fifo)))
201 return;
202
203 while (kfifo_out(&priv->fifo, &ch, 1))
204 tty_insert_flip_char(port: &priv->port, ch, TTY_NORMAL);
205 tty_flip_buffer_push(port: &priv->port);
206}
207
208static int kgdb_nmi_tty_activate(struct tty_port *port, struct tty_struct *tty)
209{
210 struct kgdb_nmi_tty_priv *priv =
211 container_of(port, struct kgdb_nmi_tty_priv, port);
212
213 kgdb_nmi_port = port;
214 priv->timer.expires = jiffies + (HZ/100);
215 add_timer(timer: &priv->timer);
216
217 return 0;
218}
219
220static void kgdb_nmi_tty_shutdown(struct tty_port *port)
221{
222 struct kgdb_nmi_tty_priv *priv =
223 container_of(port, struct kgdb_nmi_tty_priv, port);
224
225 del_timer(timer: &priv->timer);
226 kgdb_nmi_port = NULL;
227}
228
229static const struct tty_port_operations kgdb_nmi_tty_port_ops = {
230 .activate = kgdb_nmi_tty_activate,
231 .shutdown = kgdb_nmi_tty_shutdown,
232};
233
234static int kgdb_nmi_tty_install(struct tty_driver *drv, struct tty_struct *tty)
235{
236 struct kgdb_nmi_tty_priv *priv;
237 int ret;
238
239 priv = kzalloc(size: sizeof(*priv), GFP_KERNEL);
240 if (!priv)
241 return -ENOMEM;
242
243 INIT_KFIFO(priv->fifo);
244 timer_setup(&priv->timer, kgdb_nmi_tty_receiver, 0);
245 tty_port_init(port: &priv->port);
246 priv->port.ops = &kgdb_nmi_tty_port_ops;
247 tty->driver_data = priv;
248
249 ret = tty_port_install(port: &priv->port, driver: drv, tty);
250 if (ret) {
251 pr_err("%s: can't install tty port: %d\n", __func__, ret);
252 goto err;
253 }
254 return 0;
255err:
256 tty_port_destroy(port: &priv->port);
257 kfree(objp: priv);
258 return ret;
259}
260
261static void kgdb_nmi_tty_cleanup(struct tty_struct *tty)
262{
263 struct kgdb_nmi_tty_priv *priv = tty->driver_data;
264
265 tty->driver_data = NULL;
266 tty_port_destroy(port: &priv->port);
267 kfree(objp: priv);
268}
269
270static int kgdb_nmi_tty_open(struct tty_struct *tty, struct file *file)
271{
272 struct kgdb_nmi_tty_priv *priv = tty->driver_data;
273 unsigned int mode = file->f_flags & O_ACCMODE;
274 int ret;
275
276 ret = tty_port_open(port: &priv->port, tty, filp: file);
277 if (!ret && (mode == O_RDONLY || mode == O_RDWR))
278 atomic_inc(v: &kgdb_nmi_num_readers);
279
280 return ret;
281}
282
283static void kgdb_nmi_tty_close(struct tty_struct *tty, struct file *file)
284{
285 struct kgdb_nmi_tty_priv *priv = tty->driver_data;
286 unsigned int mode = file->f_flags & O_ACCMODE;
287
288 if (mode == O_RDONLY || mode == O_RDWR)
289 atomic_dec(v: &kgdb_nmi_num_readers);
290
291 tty_port_close(port: &priv->port, tty, filp: file);
292}
293
294static void kgdb_nmi_tty_hangup(struct tty_struct *tty)
295{
296 struct kgdb_nmi_tty_priv *priv = tty->driver_data;
297
298 tty_port_hangup(port: &priv->port);
299}
300
301static unsigned int kgdb_nmi_tty_write_room(struct tty_struct *tty)
302{
303 /* Actually, we can handle any amount as we use polled writes. */
304 return 2048;
305}
306
307static ssize_t kgdb_nmi_tty_write(struct tty_struct *tty, const u8 *buf,
308 size_t 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
317static 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
327int kgdb_register_nmi_console(void)
328{
329 int ret;
330
331 if (!arch_kgdb_ops.enable_nmi)
332 return 0;
333
334 kgdb_nmi_tty_driver = tty_alloc_driver(1, TTY_DRIVER_REAL_RAW);
335 if (IS_ERR(ptr: kgdb_nmi_tty_driver)) {
336 pr_err("%s: cannot allocate tty\n", __func__);
337 return PTR_ERR(ptr: kgdb_nmi_tty_driver);
338 }
339 kgdb_nmi_tty_driver->driver_name = "ttyNMI";
340 kgdb_nmi_tty_driver->name = "ttyNMI";
341 kgdb_nmi_tty_driver->num = 1;
342 kgdb_nmi_tty_driver->type = TTY_DRIVER_TYPE_SERIAL;
343 kgdb_nmi_tty_driver->subtype = SERIAL_TYPE_NORMAL;
344 kgdb_nmi_tty_driver->init_termios = tty_std_termios;
345 tty_termios_encode_baud_rate(termios: &kgdb_nmi_tty_driver->init_termios,
346 KGDB_NMI_BAUD, KGDB_NMI_BAUD);
347 tty_set_operations(driver: kgdb_nmi_tty_driver, op: &kgdb_nmi_tty_ops);
348
349 ret = tty_register_driver(driver: kgdb_nmi_tty_driver);
350 if (ret) {
351 pr_err("%s: can't register tty driver: %d\n", __func__, ret);
352 goto err_drv_reg;
353 }
354
355 register_console(&kgdb_nmi_console);
356
357 return 0;
358err_drv_reg:
359 tty_driver_kref_put(driver: kgdb_nmi_tty_driver);
360 return ret;
361}
362EXPORT_SYMBOL_GPL(kgdb_register_nmi_console);
363
364int kgdb_unregister_nmi_console(void)
365{
366 int ret;
367
368 if (!arch_kgdb_ops.enable_nmi)
369 return 0;
370 arch_kgdb_ops.enable_nmi(0);
371
372 ret = unregister_console(&kgdb_nmi_console);
373 if (ret)
374 return ret;
375
376 tty_unregister_driver(driver: kgdb_nmi_tty_driver);
377 tty_driver_kref_put(driver: kgdb_nmi_tty_driver);
378
379 return 0;
380}
381EXPORT_SYMBOL_GPL(kgdb_unregister_nmi_console);
382

source code of linux/drivers/tty/serial/kgdb_nmi.c