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