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/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         arch_kgdb_ops.enable_nmi(1);
  50
  51         /* The NMI console uses the dbg_io_ops to issue console messages. To
  52          * avoid duplicate messages during kdb sessions we must inform kdb's
  53          * I/O utilities that messages sent to the console will automatically
  54          * be displayed on the dbg_io.
  55          */
  56         dbg_io_ops->is_console = true;
  57
  58         return 0;
  59 }
  60
  61 static void kgdb_nmi_console_write(struct console *co, const char *s, uint c)
  62 {
  63         int i;
  64
  65         for (i = 0; i < c; i++)
  66                 dbg_io_ops->write_char(s[i]);
  67 }
  68
  69 static struct tty_driver *kgdb_nmi_tty_driver;
  70
  71 static struct tty_driver *kgdb_nmi_console_device(struct console *co, int *idx)
  72 {
  73         *idx = co->index;
  74         return kgdb_nmi_tty_driver;
  75 }
  76
  77 static struct console kgdb_nmi_console = {
  78         .name   = "ttyNMI",
  79         .setup  = kgdb_nmi_console_setup,
  80         .write  = kgdb_nmi_console_write,
  81         .device = kgdb_nmi_console_device,
  82         .flags  = CON_PRINTBUFFER | CON_ANYTIME,
  83         .index  = -1,
  84 };
  85
  86 /*
  87  * This is usually the maximum rate on debug ports. We make fifo large enough
  88  * to make copy-pasting to the terminal usable.
  89  */
  90 #define KGDB_NMI_BAUD           115200
  91 #define KGDB_NMI_FIFO_SIZE      roundup_pow_of_two(KGDB_NMI_BAUD / 8 / HZ)
  92
  93 struct kgdb_nmi_tty_priv {
  94         struct tty_port port;
  95         struct timer_list timer;
  96         STRUCT_KFIFO(char, KGDB_NMI_FIFO_SIZE) fifo;
  97 };
  98
  99 static struct tty_port *kgdb_nmi_port;
 100
 101 static void kgdb_tty_recv(int ch)
 102 {
 103         struct kgdb_nmi_tty_priv *priv;
 104         char c = ch;
 105
 106         if (!kgdb_nmi_port || ch < 0)
 107                 return;
 108         /*
 109          * Can't use port->tty->driver_data as tty might be not there. Timer
 110          * will check for tty and will get the ref, but here we don't have to
 111          * do that, and actually, we can't: we're in NMI context, no locks are
 112          * possible.
 113          */
 114         priv = container_of(kgdb_nmi_port, struct kgdb_nmi_tty_priv, port);
 115         kfifo_in(&priv->fifo, &c, 1);
 116 }
 117
 118 static int kgdb_nmi_poll_one_knock(void)
 119 {
 120         static int n;
 121         int c = -1;
 122         const char *magic = kgdb_nmi_magic;
 123         size_t m = strlen(magic);
 124         bool printch = 0;
 125
 126         c = dbg_io_ops->read_char();
 127         if (c == NO_POLL_CHAR)
 128                 return c;
 129
 130         if (!kgdb_nmi_knock && (c == '\r' || c == '\n')) {
 131                 return 1;
 132         } else if (c == magic[n]) {
 133                 n = (n + 1) % m;
 134                 if (!n)
 135                         return 1;
 136                 printch = 1;
 137         } else {
 138                 n = 0;
 139         }
 140
 141         if (atomic_read(&kgdb_nmi_num_readers)) {
 142                 kgdb_tty_recv(c);
 143                 return 0;
 144         }
 145
 146         if (printch) {
 147                 kdb_printf("%c", c);
 148                 return 0;
 149         }
 150
 151         kdb_printf("\r%s %s to enter the debugger> %*s",
 152                    kgdb_nmi_knock ? "Type" : "Hit",
 153                    kgdb_nmi_knock ? magic  : "<return>", (int)m, "");
 154         while (m--)
 155                 kdb_printf("\b");
 156         return 0;
 157 }
 158
 159 /**
 160  * kgdb_nmi_poll_knock - Check if it is time to enter the debugger
 161  *
 162  * "Serial ports are often noisy, especially when muxed over another port (we
 163  * often use serial over the headset connector). Noise on the async command
 164  * line just causes characters that are ignored, on a command line that blocked
 165  * execution noise would be catastrophic." -- Colin Cross
 166  *
 167  * So, this function implements KGDB/KDB knocking on the serial line: we won't
 168  * enter the debugger until we receive a known magic phrase (which is actually
 169  * "$3#33", known as "escape to KDB" command. There is also a relaxed variant
 170  * of knocking, i.e. just pressing the return key is enough to enter the
 171  * debugger. And if knocking is disabled, the function always returns 1.
 172  */
 173 bool kgdb_nmi_poll_knock(void)
 174 {
 175         if (kgdb_nmi_knock < 0)
 176                 return 1;
 177
 178         while (1) {
 179                 int ret;
 180
 181                 ret = kgdb_nmi_poll_one_knock();
 182                 if (ret == NO_POLL_CHAR)
 183                         return 0;
 184                 else if (ret == 1)
 185                         break;
 186         }
 187         return 1;
 188 }
 189
 190 /*
 191  * The tasklet is cheap, it does not cause wakeups when reschedules itself,
 192  * instead it waits for the next tick.
 193  */
 194 static void kgdb_nmi_tty_receiver(unsigned long data)
 195 {
 196         struct kgdb_nmi_tty_priv *priv = (void *)data;
 197         char ch;
 198
 199         priv->timer.expires = jiffies + (HZ/100);
 200         add_timer(&priv->timer);
 201
 202         if (likely(!atomic_read(&kgdb_nmi_num_readers) ||
 203                    !kfifo_len(&priv->fifo)))
 204                 return;
 205
 206         while (kfifo_out(&priv->fifo, &ch, 1))
 207                 tty_insert_flip_char(&priv->port, ch, TTY_NORMAL);
 208         tty_flip_buffer_push(&priv->port);
 209 }
 210
 211 static int kgdb_nmi_tty_activate(struct tty_port *port, struct tty_struct *tty)
 212 {
 213         struct kgdb_nmi_tty_priv *priv =
 214             container_of(port, struct kgdb_nmi_tty_priv, port);
 215
 216         kgdb_nmi_port = port;
 217         priv->timer.expires = jiffies + (HZ/100);
 218         add_timer(&priv->timer);
 219
 220         return 0;
 221 }
 222
 223 static void kgdb_nmi_tty_shutdown(struct tty_port *port)
 224 {
 225         struct kgdb_nmi_tty_priv *priv =
 226             container_of(port, struct kgdb_nmi_tty_priv, port);
 227
 228         del_timer(&priv->timer);
 229         kgdb_nmi_port = NULL;
 230 }
 231
 232 static const struct tty_port_operations kgdb_nmi_tty_port_ops = {
 233         .activate       = kgdb_nmi_tty_activate,
 234         .shutdown       = kgdb_nmi_tty_shutdown,
 235 };
 236
 237 static int kgdb_nmi_tty_install(struct tty_driver *drv, struct tty_struct *tty)
 238 {
 239         struct kgdb_nmi_tty_priv *priv;
 240         int ret;
 241
 242         priv = kzalloc(sizeof(*priv), GFP_KERNEL);
 243         if (!priv)
 244                 return -ENOMEM;
 245
 246         INIT_KFIFO(priv->fifo);
 247         setup_timer(&priv->timer, kgdb_nmi_tty_receiver, (unsigned long)priv);
 248         tty_port_init(&priv->port);
 249         priv->port.ops = &kgdb_nmi_tty_port_ops;
 250         tty->driver_data = priv;
 251
 252         ret = tty_port_install(&priv->port, drv, tty);
 253         if (ret) {
 254                 pr_err("%s: can't install tty port: %d\n", __func__, ret);
 255                 goto err;
 256         }
 257         return 0;
 258 err:
 259         tty_port_destroy(&priv->port);
 260         kfree(priv);
 261         return ret;
 262 }
 263
 264 static void kgdb_nmi_tty_cleanup(struct tty_struct *tty)
 265 {
 266         struct kgdb_nmi_tty_priv *priv = tty->driver_data;
 267
 268         tty->driver_data = NULL;
 269         tty_port_destroy(&priv->port);
 270         kfree(priv);
 271 }
 272
 273 static int kgdb_nmi_tty_open(struct tty_struct *tty, struct file *file)
 274 {
 275         struct kgdb_nmi_tty_priv *priv = tty->driver_data;
 276         unsigned int mode = file->f_flags & O_ACCMODE;
 277         int ret;
 278
 279         ret = tty_port_open(&priv->port, tty, file);
 280         if (!ret && (mode == O_RDONLY || mode == O_RDWR))
 281                 atomic_inc(&kgdb_nmi_num_readers);
 282
 283         return ret;
 284 }
 285
 286 static void kgdb_nmi_tty_close(struct tty_struct *tty, struct file *file)
 287 {
 288         struct kgdb_nmi_tty_priv *priv = tty->driver_data;
 289         unsigned int mode = file->f_flags & O_ACCMODE;
 290
 291         if (mode == O_RDONLY || mode == O_RDWR)
 292                 atomic_dec(&kgdb_nmi_num_readers);
 293
 294         tty_port_close(&priv->port, tty, file);
 295 }
 296
 297 static void kgdb_nmi_tty_hangup(struct tty_struct *tty)
 298 {
 299         struct kgdb_nmi_tty_priv *priv = tty->driver_data;
 300
 301         tty_port_hangup(&priv->port);
 302 }
 303
 304 static int kgdb_nmi_tty_write_room(struct tty_struct *tty)
 305 {
 306         /* Actually, we can handle any amount as we use polled writes. */
 307         return 2048;
 308 }
 309
 310 static int kgdb_nmi_tty_write(struct tty_struct *tty, const unchar *buf, int c)
 311 {
 312         int i;
 313
 314         for (i = 0; i < c; i++)
 315                 dbg_io_ops->write_char(buf[i]);
 316         return c;
 317 }
 318
 319 static const struct tty_operations kgdb_nmi_tty_ops = {
 320         .open           = kgdb_nmi_tty_open,
 321         .close          = kgdb_nmi_tty_close,
 322         .install        = kgdb_nmi_tty_install,
 323         .cleanup        = kgdb_nmi_tty_cleanup,
 324         .hangup         = kgdb_nmi_tty_hangup,
 325         .write_room     = kgdb_nmi_tty_write_room,
 326         .write          = kgdb_nmi_tty_write,
 327 };
 328
 329 int kgdb_register_nmi_console(void)
 330 {
 331         int ret;
 332
 333         if (!arch_kgdb_ops.enable_nmi)
 334                 return 0;
 335
 336         kgdb_nmi_tty_driver = alloc_tty_driver(1);
 337         if (!kgdb_nmi_tty_driver) {
 338                 pr_err("%s: cannot allocate tty\n", __func__);
 339                 return -ENOMEM;
 340         }
 341         kgdb_nmi_tty_driver->driver_name        = "ttyNMI";
 342         kgdb_nmi_tty_driver->name               = "ttyNMI";
 343         kgdb_nmi_tty_driver->num                = 1;
 344         kgdb_nmi_tty_driver->type               = TTY_DRIVER_TYPE_SERIAL;
 345         kgdb_nmi_tty_driver->subtype            = SERIAL_TYPE_NORMAL;
 346         kgdb_nmi_tty_driver->flags              = TTY_DRIVER_REAL_RAW;
 347         kgdb_nmi_tty_driver->init_termios       = tty_std_termios;
 348         tty_termios_encode_baud_rate(&kgdb_nmi_tty_driver->init_termios,
 349                                      KGDB_NMI_BAUD, KGDB_NMI_BAUD);
 350         tty_set_operations(kgdb_nmi_tty_driver, &kgdb_nmi_tty_ops);
 351
 352         ret = tty_register_driver(kgdb_nmi_tty_driver);
 353         if (ret) {
 354                 pr_err("%s: can't register tty driver: %d\n", __func__, ret);
 355                 goto err_drv_reg;
 356         }
 357
 358         register_console(&kgdb_nmi_console);
 359
 360         return 0;
 361 err_drv_reg:
 362         put_tty_driver(kgdb_nmi_tty_driver);
 363         return ret;
 364 }
 365 EXPORT_SYMBOL_GPL(kgdb_register_nmi_console);
 366
 367 int kgdb_unregister_nmi_console(void)
 368 {
 369         int ret;
 370
 371         if (!arch_kgdb_ops.enable_nmi)
 372                 return 0;
 373         arch_kgdb_ops.enable_nmi(0);
 374
 375         ret = unregister_console(&kgdb_nmi_console);
 376         if (ret)
 377                 return ret;
 378
 379         ret = tty_unregister_driver(kgdb_nmi_tty_driver);
 380         if (ret)
 381                 return ret;
 382         put_tty_driver(kgdb_nmi_tty_driver);
 383
 384         return 0;
 385 }
 386 EXPORT_SYMBOL_GPL(kgdb_unregister_nmi_console);