1 files changed, 381 insertions, 0 deletions
diff --git a/drivers/tty/serial/kgdb_nmi.c b/drivers/tty/serial/kgdb_nmi.c
new file mode 100644
index 0000000000..e93850f644
--- /dev/null
+++ b/drivers/tty/serial/kgdb_nmi.c
@@ -0,0 +1,381 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KGDB NMI serial console
+ *
+ * Copyright 2010 Google, Inc.
+ *		  Arve Hjønnevåg <arve@android.com>
+ *		  Colin Cross <ccross@android.com>
+ * Copyright 2012 Linaro Ltd.
+ *		  Anton Vorontsov <anton.vorontsov@linaro.org>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/compiler.h>
+#include <linux/slab.h>
+#include <linux/errno.h>
+#include <linux/atomic.h>
+#include <linux/console.h>
+#include <linux/tty.h>
+#include <linux/tty_driver.h>
+#include <linux/tty_flip.h>
+#include <linux/serial_core.h>
+#include <linux/interrupt.h>
+#include <linux/hrtimer.h>
+#include <linux/tick.h>
+#include <linux/kfifo.h>
+#include <linux/kgdb.h>
+#include <linux/kdb.h>
+
+static int kgdb_nmi_knock = 1;
+module_param_named(knock, kgdb_nmi_knock, int, 0600);
+MODULE_PARM_DESC(knock, "if set to 1 (default), the special '$3#33' command " \
+			"must be used to enter the debugger; when set to 0, " \
+			"hitting return key is enough to enter the debugger; " \
+			"when set to -1, the debugger is entered immediately " \
+			"upon NMI");
+
+static char *kgdb_nmi_magic = "$3#33";
+module_param_named(magic, kgdb_nmi_magic, charp, 0600);
+MODULE_PARM_DESC(magic, "magic sequence to enter NMI debugger (default $3#33)");
+
+static atomic_t kgdb_nmi_num_readers = ATOMIC_INIT(0);
+
+static int kgdb_nmi_console_setup(struct console *co, char *options)
+{
+	arch_kgdb_ops.enable_nmi(1);
+
+	/* The NMI console uses the dbg_io_ops to issue console messages. To
+	 * avoid duplicate messages during kdb sessions we must inform kdb's
+	 * I/O utilities that messages sent to the console will automatically
+	 * be displayed on the dbg_io.
+	 */
+	dbg_io_ops->cons = co;
+
+	return 0;
+}
+
+static void kgdb_nmi_console_write(struct console *co, const char *s, uint c)
+{
+	int i;
+
+	for (i = 0; i < c; i++)
+		dbg_io_ops->write_char(s[i]);
+}
+
+static struct tty_driver *kgdb_nmi_tty_driver;
+
+static struct tty_driver *kgdb_nmi_console_device(struct console *co, int *idx)
+{
+	*idx = co->index;
+	return kgdb_nmi_tty_driver;
+}
+
+static struct console kgdb_nmi_console = {
+	.name	= "ttyNMI",
+	.setup  = kgdb_nmi_console_setup,
+	.write	= kgdb_nmi_console_write,
+	.device	= kgdb_nmi_console_device,
+	.flags	= CON_PRINTBUFFER | CON_ANYTIME,
+	.index	= -1,
+};
+
+/*
+ * This is usually the maximum rate on debug ports. We make fifo large enough
+ * to make copy-pasting to the terminal usable.
+ */
+#define KGDB_NMI_BAUD		115200
+#define KGDB_NMI_FIFO_SIZE	roundup_pow_of_two(KGDB_NMI_BAUD / 8 / HZ)
+
+struct kgdb_nmi_tty_priv {
+	struct tty_port port;
+	struct timer_list timer;
+	STRUCT_KFIFO(char, KGDB_NMI_FIFO_SIZE) fifo;
+};
+
+static struct tty_port *kgdb_nmi_port;
+
+static void kgdb_tty_recv(int ch)
+{
+	struct kgdb_nmi_tty_priv *priv;
+	char c = ch;
+
+	if (!kgdb_nmi_port || ch < 0)
+		return;
+	/*
+	 * Can't use port->tty->driver_data as tty might be not there. Timer
+	 * will check for tty and will get the ref, but here we don't have to
+	 * do that, and actually, we can't: we're in NMI context, no locks are
+	 * possible.
+	 */
+	priv = container_of(kgdb_nmi_port, struct kgdb_nmi_tty_priv, port);
+	kfifo_in(&priv->fifo, &c, 1);
+}
+
+static int kgdb_nmi_poll_one_knock(void)
+{
+	static int n;
+	int c;
+	const char *magic = kgdb_nmi_magic;
+	size_t m = strlen(magic);
+	bool printch = false;
+
+	c = dbg_io_ops->read_char();
+	if (c == NO_POLL_CHAR)
+		return c;
+
+	if (!kgdb_nmi_knock && (c == '\r' || c == '\n')) {
+		return 1;
+	} else if (c == magic[n]) {
+		n = (n + 1) % m;
+		if (!n)
+			return 1;
+		printch = true;
+	} else {
+		n = 0;
+	}
+
+	if (atomic_read(&kgdb_nmi_num_readers)) {
+		kgdb_tty_recv(c);
+		return 0;
+	}
+
+	if (printch) {
+		kdb_printf("%c", c);
+		return 0;
+	}
+
+	kdb_printf("\r%s %s to enter the debugger> %*s",
+		   kgdb_nmi_knock ? "Type" : "Hit",
+		   kgdb_nmi_knock ? magic  : "<return>", (int)m, "");
+	while (m--)
+		kdb_printf("\b");
+	return 0;
+}
+
+/**
+ * kgdb_nmi_poll_knock - Check if it is time to enter the debugger
+ *
+ * "Serial ports are often noisy, especially when muxed over another port (we
+ * often use serial over the headset connector). Noise on the async command
+ * line just causes characters that are ignored, on a command line that blocked
+ * execution noise would be catastrophic." -- Colin Cross
+ *
+ * So, this function implements KGDB/KDB knocking on the serial line: we won't
+ * enter the debugger until we receive a known magic phrase (which is actually
+ * "$3#33", known as "escape to KDB" command. There is also a relaxed variant
+ * of knocking, i.e. just pressing the return key is enough to enter the
+ * debugger. And if knocking is disabled, the function always returns 1.
+ */
+bool kgdb_nmi_poll_knock(void)
+{
+	if (kgdb_nmi_knock < 0)
+		return true;
+
+	while (1) {
+		int ret;
+
+		ret = kgdb_nmi_poll_one_knock();
+		if (ret == NO_POLL_CHAR)
+			return false;
+		else if (ret == 1)
+			break;
+	}
+	return true;
+}
+
+/*
+ * The tasklet is cheap, it does not cause wakeups when reschedules itself,
+ * instead it waits for the next tick.
+ */
+static void kgdb_nmi_tty_receiver(struct timer_list *t)
+{
+	struct kgdb_nmi_tty_priv *priv = from_timer(priv, t, timer);
+	char ch;
+
+	priv->timer.expires = jiffies + (HZ/100);
+	add_timer(&priv->timer);
+
+	if (likely(!atomic_read(&kgdb_nmi_num_readers) ||
+		   !kfifo_len(&priv->fifo)))
+		return;
+
+	while (kfifo_out(&priv->fifo, &ch, 1))
+		tty_insert_flip_char(&priv->port, ch, TTY_NORMAL);
+	tty_flip_buffer_push(&priv->port);
+}
+
+static int kgdb_nmi_tty_activate(struct tty_port *port, struct tty_struct *tty)
+{
+	struct kgdb_nmi_tty_priv *priv =
+	    container_of(port, struct kgdb_nmi_tty_priv, port);
+
+	kgdb_nmi_port = port;
+	priv->timer.expires = jiffies + (HZ/100);
+	add_timer(&priv->timer);
+
+	return 0;
+}
+
+static void kgdb_nmi_tty_shutdown(struct tty_port *port)
+{
+	struct kgdb_nmi_tty_priv *priv =
+	    container_of(port, struct kgdb_nmi_tty_priv, port);
+
+	del_timer(&priv->timer);
+	kgdb_nmi_port = NULL;
+}
+
+static const struct tty_port_operations kgdb_nmi_tty_port_ops = {
+	.activate	= kgdb_nmi_tty_activate,
+	.shutdown	= kgdb_nmi_tty_shutdown,
+};
+
+static int kgdb_nmi_tty_install(struct tty_driver *drv, struct tty_struct *tty)
+{
+	struct kgdb_nmi_tty_priv *priv;
+	int ret;
+
+	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	INIT_KFIFO(priv->fifo);
+	timer_setup(&priv->timer, kgdb_nmi_tty_receiver, 0);
+	tty_port_init(&priv->port);
+	priv->port.ops = &kgdb_nmi_tty_port_ops;
+	tty->driver_data = priv;
+
+	ret = tty_port_install(&priv->port, drv, tty);
+	if (ret) {
+		pr_err("%s: can't install tty port: %d\n", __func__, ret);
+		goto err;
+	}
+	return 0;
+err:
+	tty_port_destroy(&priv->port);
+	kfree(priv);
+	return ret;
+}
+
+static void kgdb_nmi_tty_cleanup(struct tty_struct *tty)
+{
+	struct kgdb_nmi_tty_priv *priv = tty->driver_data;
+
+	tty->driver_data = NULL;
+	tty_port_destroy(&priv->port);
+	kfree(priv);
+}
+
+static int kgdb_nmi_tty_open(struct tty_struct *tty, struct file *file)
+{
+	struct kgdb_nmi_tty_priv *priv = tty->driver_data;
+	unsigned int mode = file->f_flags & O_ACCMODE;
+	int ret;
+
+	ret = tty_port_open(&priv->port, tty, file);
+	if (!ret && (mode == O_RDONLY || mode == O_RDWR))
+		atomic_inc(&kgdb_nmi_num_readers);
+
+	return ret;
+}
+
+static void kgdb_nmi_tty_close(struct tty_struct *tty, struct file *file)
+{
+	struct kgdb_nmi_tty_priv *priv = tty->driver_data;
+	unsigned int mode = file->f_flags & O_ACCMODE;
+
+	if (mode == O_RDONLY || mode == O_RDWR)
+		atomic_dec(&kgdb_nmi_num_readers);
+
+	tty_port_close(&priv->port, tty, file);
+}
+
+static void kgdb_nmi_tty_hangup(struct tty_struct *tty)
+{
+	struct kgdb_nmi_tty_priv *priv = tty->driver_data;
+
+	tty_port_hangup(&priv->port);
+}
+
+static unsigned int kgdb_nmi_tty_write_room(struct tty_struct *tty)
+{
+	/* Actually, we can handle any amount as we use polled writes. */
+	return 2048;
+}
+
+static ssize_t kgdb_nmi_tty_write(struct tty_struct *tty, const u8 *buf,
+				  size_t c)
+{
+	int i;
+
+	for (i = 0; i < c; i++)
+		dbg_io_ops->write_char(buf[i]);
+	return c;
+}
+
+static const struct tty_operations kgdb_nmi_tty_ops = {
+	.open		= kgdb_nmi_tty_open,
+	.close		= kgdb_nmi_tty_close,
+	.install	= kgdb_nmi_tty_install,
+	.cleanup	= kgdb_nmi_tty_cleanup,
+	.hangup		= kgdb_nmi_tty_hangup,
+	.write_room	= kgdb_nmi_tty_write_room,
+	.write		= kgdb_nmi_tty_write,
+};
+
+int kgdb_register_nmi_console(void)
+{
+	int ret;
+
+	if (!arch_kgdb_ops.enable_nmi)
+		return 0;
+
+	kgdb_nmi_tty_driver = tty_alloc_driver(1, TTY_DRIVER_REAL_RAW);
+	if (IS_ERR(kgdb_nmi_tty_driver)) {
+		pr_err("%s: cannot allocate tty\n", __func__);
+		return PTR_ERR(kgdb_nmi_tty_driver);
+	}
+	kgdb_nmi_tty_driver->driver_name	= "ttyNMI";
+	kgdb_nmi_tty_driver->name		= "ttyNMI";
+	kgdb_nmi_tty_driver->num		= 1;
+	kgdb_nmi_tty_driver->type		= TTY_DRIVER_TYPE_SERIAL;
+	kgdb_nmi_tty_driver->subtype		= SERIAL_TYPE_NORMAL;
+	kgdb_nmi_tty_driver->init_termios	= tty_std_termios;
+	tty_termios_encode_baud_rate(&kgdb_nmi_tty_driver->init_termios,
+				     KGDB_NMI_BAUD, KGDB_NMI_BAUD);
+	tty_set_operations(kgdb_nmi_tty_driver, &kgdb_nmi_tty_ops);
+
+	ret = tty_register_driver(kgdb_nmi_tty_driver);
+	if (ret) {
+		pr_err("%s: can't register tty driver: %d\n", __func__, ret);
+		goto err_drv_reg;
+	}
+
+	register_console(&kgdb_nmi_console);
+
+	return 0;
+err_drv_reg:
+	tty_driver_kref_put(kgdb_nmi_tty_driver);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(kgdb_register_nmi_console);
+
+int kgdb_unregister_nmi_console(void)
+{
+	int ret;
+
+	if (!arch_kgdb_ops.enable_nmi)
+		return 0;
+	arch_kgdb_ops.enable_nmi(0);
+
+	ret = unregister_console(&kgdb_nmi_console);
+	if (ret)
+		return ret;
+
+	tty_unregister_driver(kgdb_nmi_tty_driver);
+	tty_driver_kref_put(kgdb_nmi_tty_driver);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(kgdb_unregister_nmi_console);