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/slab.h> 19 #include <linux/errno.h> 20 #include <linux/atomic.h> 21 #include <linux/console.h> 22 #include <linux/tty.h> 23 #include <linux/tty_driver.h> 24 #include <linux/tty_flip.h> 25 #include <linux/serial_core.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 atomic_t kgdb_nmi_num_readers = ATOMIC_INIT(0); 46 47 static int kgdb_nmi_console_setup(struct console *co, char *options) 48 { 49 /* The NMI console uses the dbg_io_ops to issue console messages. To 50 * avoid duplicate messages during kdb sessions we must inform kdb's 51 * I/O utilities that messages sent to the console will automatically 52 * be displayed on the dbg_io. 53 */ 54 dbg_io_ops->is_console = true; 55 56 return 0; 57 } 58 59 static void kgdb_nmi_console_write(struct console *co, const char *s, uint c) 60 { 61 int i; 62 63 for (i = 0; i < c; i++) 64 dbg_io_ops->write_char(s[i]); 65 } 66 67 static struct tty_driver *kgdb_nmi_tty_driver; 68 69 static struct tty_driver *kgdb_nmi_console_device(struct console *co, int *idx) 70 { 71 *idx = co->index; 72 return kgdb_nmi_tty_driver; 73 } 74 75 static struct console kgdb_nmi_console = { 76 .name = "ttyNMI", 77 .setup = kgdb_nmi_console_setup, 78 .write = kgdb_nmi_console_write, 79 .device = kgdb_nmi_console_device, 80 .flags = CON_PRINTBUFFER | CON_ANYTIME | CON_ENABLED, 81 .index = -1, 82 }; 83 84 /* 85 * This is usually the maximum rate on debug ports. We make fifo large enough 86 * to make copy-pasting to the terminal usable. 87 */ 88 #define KGDB_NMI_BAUD 115200 89 #define KGDB_NMI_FIFO_SIZE roundup_pow_of_two(KGDB_NMI_BAUD / 8 / HZ) 90 91 struct kgdb_nmi_tty_priv { 92 struct tty_port port; 93 struct timer_list timer; 94 STRUCT_KFIFO(char, KGDB_NMI_FIFO_SIZE) fifo; 95 }; 96 97 static struct tty_port *kgdb_nmi_port; 98 99 static void kgdb_tty_recv(int ch) 100 { 101 struct kgdb_nmi_tty_priv *priv; 102 char c = ch; 103 104 if (!kgdb_nmi_port || ch < 0) 105 return; 106 /* 107 * Can't use port->tty->driver_data as tty might be not there. Timer 108 * will check for tty and will get the ref, but here we don't have to 109 * do that, and actually, we can't: we're in NMI context, no locks are 110 * possible. 111 */ 112 priv = container_of(kgdb_nmi_port, struct kgdb_nmi_tty_priv, port); 113 kfifo_in(&priv->fifo, &c, 1); 114 } 115 116 static int kgdb_nmi_poll_one_knock(void) 117 { 118 static int n; 119 int c = -1; 120 const char *magic = kgdb_nmi_magic; 121 size_t m = strlen(magic); 122 bool printch = 0; 123 124 c = dbg_io_ops->read_char(); 125 if (c == NO_POLL_CHAR) 126 return c; 127 128 if (!kgdb_nmi_knock && (c == '\r' || c == '\n')) { 129 return 1; 130 } else if (c == magic[n]) { 131 n = (n + 1) % m; 132 if (!n) 133 return 1; 134 printch = 1; 135 } else { 136 n = 0; 137 } 138 139 if (atomic_read(&kgdb_nmi_num_readers)) { 140 kgdb_tty_recv(c); 141 return 0; 142 } 143 144 if (printch) { 145 kdb_printf("%c", c); 146 return 0; 147 } 148 149 kdb_printf("\r%s %s to enter the debugger> %*s", 150 kgdb_nmi_knock ? "Type" : "Hit", 151 kgdb_nmi_knock ? magic : "<return>", (int)m, ""); 152 while (m--) 153 kdb_printf("\b"); 154 return 0; 155 } 156 157 /** 158 * kgdb_nmi_poll_knock - Check if it is time to enter the debugger 159 * 160 * "Serial ports are often noisy, especially when muxed over another port (we 161 * often use serial over the headset connector). Noise on the async command 162 * line just causes characters that are ignored, on a command line that blocked 163 * execution noise would be catastrophic." -- Colin Cross 164 * 165 * So, this function implements KGDB/KDB knocking on the serial line: we won't 166 * enter the debugger until we receive a known magic phrase (which is actually 167 * "$3#33", known as "escape to KDB" command. There is also a relaxed variant 168 * of knocking, i.e. just pressing the return key is enough to enter the 169 * debugger. And if knocking is disabled, the function always returns 1. 170 */ 171 bool kgdb_nmi_poll_knock(void) 172 { 173 if (kgdb_nmi_knock < 0) 174 return 1; 175 176 while (1) { 177 int ret; 178 179 ret = kgdb_nmi_poll_one_knock(); 180 if (ret == NO_POLL_CHAR) 181 return 0; 182 else if (ret == 1) 183 break; 184 } 185 return 1; 186 } 187 188 /* 189 * The tasklet is cheap, it does not cause wakeups when reschedules itself, 190 * instead it waits for the next tick. 191 */ 192 static void kgdb_nmi_tty_receiver(unsigned long data) 193 { 194 struct kgdb_nmi_tty_priv *priv = (void *)data; 195 char ch; 196 197 priv->timer.expires = jiffies + (HZ/100); 198 add_timer(&priv->timer); 199 200 if (likely(!atomic_read(&kgdb_nmi_num_readers) || 201 !kfifo_len(&priv->fifo))) 202 return; 203 204 while (kfifo_out(&priv->fifo, &ch, 1)) 205 tty_insert_flip_char(&priv->port, ch, TTY_NORMAL); 206 tty_flip_buffer_push(&priv->port); 207 } 208 209 static int kgdb_nmi_tty_activate(struct tty_port *port, struct tty_struct *tty) 210 { 211 struct kgdb_nmi_tty_priv *priv = 212 container_of(port, struct kgdb_nmi_tty_priv, port); 213 214 kgdb_nmi_port = port; 215 priv->timer.expires = jiffies + (HZ/100); 216 add_timer(&priv->timer); 217 218 return 0; 219 } 220 221 static void kgdb_nmi_tty_shutdown(struct tty_port *port) 222 { 223 struct kgdb_nmi_tty_priv *priv = 224 container_of(port, struct kgdb_nmi_tty_priv, port); 225 226 del_timer(&priv->timer); 227 kgdb_nmi_port = NULL; 228 } 229 230 static const struct tty_port_operations kgdb_nmi_tty_port_ops = { 231 .activate = kgdb_nmi_tty_activate, 232 .shutdown = kgdb_nmi_tty_shutdown, 233 }; 234 235 static int kgdb_nmi_tty_install(struct tty_driver *drv, struct tty_struct *tty) 236 { 237 struct kgdb_nmi_tty_priv *priv; 238 int ret; 239 240 priv = kzalloc(sizeof(*priv), GFP_KERNEL); 241 if (!priv) 242 return -ENOMEM; 243 244 INIT_KFIFO(priv->fifo); 245 setup_timer(&priv->timer, kgdb_nmi_tty_receiver, (unsigned long)priv); 246 tty_port_init(&priv->port); 247 priv->port.ops = &kgdb_nmi_tty_port_ops; 248 tty->driver_data = priv; 249 250 ret = tty_port_install(&priv->port, drv, tty); 251 if (ret) { 252 pr_err("%s: can't install tty port: %d\n", __func__, ret); 253 goto err; 254 } 255 return 0; 256 err: 257 tty_port_destroy(&priv->port); 258 kfree(priv); 259 return ret; 260 } 261 262 static void kgdb_nmi_tty_cleanup(struct tty_struct *tty) 263 { 264 struct kgdb_nmi_tty_priv *priv = tty->driver_data; 265 266 tty->driver_data = NULL; 267 tty_port_destroy(&priv->port); 268 kfree(priv); 269 } 270 271 static int kgdb_nmi_tty_open(struct tty_struct *tty, struct file *file) 272 { 273 struct kgdb_nmi_tty_priv *priv = tty->driver_data; 274 unsigned int mode = file->f_flags & O_ACCMODE; 275 int ret; 276 277 ret = tty_port_open(&priv->port, tty, file); 278 if (!ret && (mode == O_RDONLY || mode == O_RDWR)) 279 atomic_inc(&kgdb_nmi_num_readers); 280 281 return ret; 282 } 283 284 static void kgdb_nmi_tty_close(struct tty_struct *tty, struct file *file) 285 { 286 struct kgdb_nmi_tty_priv *priv = tty->driver_data; 287 unsigned int mode = file->f_flags & O_ACCMODE; 288 289 if (mode == O_RDONLY || mode == O_RDWR) 290 atomic_dec(&kgdb_nmi_num_readers); 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 int 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 = alloc_tty_driver(1); 335 if (!kgdb_nmi_tty_driver) { 336 pr_err("%s: cannot allocate tty\n", __func__); 337 return -ENOMEM; 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->flags = TTY_DRIVER_REAL_RAW; 345 kgdb_nmi_tty_driver->init_termios = tty_std_termios; 346 tty_termios_encode_baud_rate(&kgdb_nmi_tty_driver->init_termios, 347 KGDB_NMI_BAUD, KGDB_NMI_BAUD); 348 tty_set_operations(kgdb_nmi_tty_driver, &kgdb_nmi_tty_ops); 349 350 ret = tty_register_driver(kgdb_nmi_tty_driver); 351 if (ret) { 352 pr_err("%s: can't register tty driver: %d\n", __func__, ret); 353 goto err_drv_reg; 354 } 355 356 register_console(&kgdb_nmi_console); 357 arch_kgdb_ops.enable_nmi(1); 358 359 return 0; 360 err_drv_reg: 361 put_tty_driver(kgdb_nmi_tty_driver); 362 return ret; 363 } 364 EXPORT_SYMBOL_GPL(kgdb_register_nmi_console); 365 366 int kgdb_unregister_nmi_console(void) 367 { 368 int ret; 369 370 if (!arch_kgdb_ops.enable_nmi) 371 return 0; 372 arch_kgdb_ops.enable_nmi(0); 373 374 ret = unregister_console(&kgdb_nmi_console); 375 if (ret) 376 return ret; 377 378 ret = tty_unregister_driver(kgdb_nmi_tty_driver); 379 if (ret) 380 return ret; 381 put_tty_driver(kgdb_nmi_tty_driver); 382 383 return 0; 384 } 385 EXPORT_SYMBOL_GPL(kgdb_unregister_nmi_console); 386