This command disables NMI-entry. If NMI source has been previously shared with a serial console ("debug port"), this effectively releases the port from KDB exclusive use, and makes the console available for normal use.

Of course, NMI can be reenabled, enable_nmi modparam is used for that:

echo 1 > /sys/module/kdb/parameters/enable_nmi

Signed-off-by: Anton Vorontsov anton.vorontsov@linaro.org --- kernel/debug/kdb/kdb_main.c | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+)

diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c index 31df170..9fadff1 100644 --- a/kernel/debug/kdb/kdb_main.c +++ b/kernel/debug/kdb/kdb_main.c @@ -21,6 +21,7 @@ #include <linux/smp.h> #include <linux/utsname.h> #include <linux/vmalloc.h> +#include <linux/atomic.h> #include <linux/module.h> #include <linux/mm.h> #include <linux/init.h> @@ -2107,6 +2108,32 @@ static int kdb_dmesg(int argc, const char **argv) return 0; } #endif /* CONFIG_PRINTK */ + +/* Make sure we balance enable/disable calls, must disable first. */ +static atomic_t kdb_nmi_disabled; + +static int kdb_disable_nmi(int argc, const char *argv[]) +{ + if (atomic_read(&kdb_nmi_disabled)) + return 0; + atomic_set(&kdb_nmi_disabled, 1); + kgdb_enable_nmi(0); + return 0; +} + +static int kdb_param_enable_nmi(const char *val, const struct kernel_param *kp) +{ + if (!atomic_add_unless(&kdb_nmi_disabled, -1, 0)) + return -EINVAL; + kgdb_enable_nmi(1); + return 0; +} + +static const struct kernel_param_ops kdb_param_ops_enable_nmi = { + .set = kdb_param_enable_nmi, +}; +module_param_cb(enable_nmi, &kdb_param_ops_enable_nmi, NULL, 0600); + /* * kdb_cpu - This function implements the 'cpu' command. * cpu [<cpunum>] @@ -2851,6 +2878,8 @@ static void __init kdb_inittab(void) kdb_register_repeat("dmesg", kdb_dmesg, "[lines]", "Display syslog buffer", 0, KDB_REPEAT_NONE); #endif + kdb_register_repeat("disable_nmi", kdb_disable_nmi, "", + "Disable NMI entry to KDB", 0, KDB_REPEAT_NONE); kdb_register_repeat("defcmd", kdb_defcmd, "name "usage" "help"", "Define a set of commands, down to endefcmd", 0, KDB_REPEAT_NONE); kdb_register_repeat("kill", kdb_kill, "<-signal> <pid>",

It was noticed that polling drivers (like KGDB) are not able to use serial ports if the ports were not previously initialized via console. I.e. when booting with console=ttyAMA0 kgdboc=ttyAMA0, everything works fine, but with console=ttyFOO kgdboc=ttyAMA0, the kgdboc doesn't work.

This is because we don't initialize the hardware. Calling ->startup() is not an option, because drivers request interrupts there, and drivers fail to handle situations when tty isn't opened with interrupts enabled.

So, we have to implement a new callback (actually, tty_ops already have a similar callback), which does everything needed to initialize just the hardware.

Signed-off-by: Anton Vorontsov anton.vorontsov@linaro.org --- drivers/tty/serial/serial_core.c | 17 +++++++++++++++++ include/linux/serial_core.h | 1 + 2 files changed, 18 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 046279c..dcb2d5a 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -2129,6 +2129,7 @@ static int uart_poll_init(struct tty_driver *driver, int line, char *options) int bits = 8; int parity = 'n'; int flow = 'n'; + int ret;

if (!state || !state->uart_port) return -1; @@ -2137,6 +2138,22 @@ static int uart_poll_init(struct tty_driver *driver, int line, char *options) if (!(port->ops->poll_get_char && port->ops->poll_put_char)) return -1;

+ if (port->ops->poll_init) { + struct tty_port *tport = &state->port; + + ret = 0; + mutex_lock(&tport->mutex); + /* + * We don't set ASYNCB_INITIALIZED as we only initialized the + * hw, e.g. state->xmit is still uninitialized. + */ + if (!test_bit(ASYNCB_INITIALIZED, &tport->flags)) + ret = port->ops->poll_init(port); + mutex_unlock(&tport->mutex); + if (ret) + return ret; + } + if (options) { uart_parse_options(options, &baud, &parity, &bits, &flow); return uart_set_options(port, NULL, baud, parity, bits, flow); diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h index 7cf0b68..822c887 100644 --- a/include/linux/serial_core.h +++ b/include/linux/serial_core.h @@ -274,6 +274,7 @@ struct uart_ops { int (*verify_port)(struct uart_port *, struct serial_struct *); int (*ioctl)(struct uart_port *, unsigned int, unsigned long); #ifdef CONFIG_CONSOLE_POLL + int (*poll_init)(struct uart_port *); void (*poll_put_char)(struct uart_port *, unsigned char); int (*poll_get_char)(struct uart_port *); #endif

This patch implements a new callback: clear_irqs. It is used for the cases when KDB-entry (e.g. NMI) and KDB IO (e.g. serial port) shares the same interrupt. To get the idea, let's take some real example (ARM machine): we have a serial port which interrupt is routed to an NMI, and the interrupt is used to enter KDB. Once there is some activity on the serial port, the CPU receives NMI exception, and we fall into KDB shell. So, it is our "debug console", and it is able to interrupt (and thus debug) even IRQ handlers themselves.

When used that way, the interrupt never reaches serial driver's IRQ handler routine, which means that serial driver will not silence the interrupt. NMIs behaviour are quite arch-specific, and we can't assume that we can use them as ordinary IRQs, e.g. on some arches (like ARM) we can't handle data aborts, the behaviour is undefined then. So we can't just handle execution to serial driver's IRQ handler from the NMI context once we're done with KDB (plus this would defeat the debugger's purpose: we want the NMI handler be as simple as possible, so it will have less chances to hang).

So, given that have to deal with it somehow, we have two options:

1. Implement something that clears the interrupt; 2. Implement a whole new concept of grabbing tty for exclusive KDB use, plus implement mask/unmask callbacks, i.e.: - Since consoles might use ttys w/o opending them, we would have to make kdb respect CON_ENABLED flag (maybe a good idea to do it anyway); - Add 'bool exclusive' argument to tty_find_polling_driver(), if set to 1, the function will refuse to return an already opened tty; and will use the flag in tty_reopen() to not allow multiple users (there are already checks for pty masters, which are "open once" ttys); - Once we got the tty exclusively, we would need to call some new uart->mask_all_but_rx_interrupts call before we want to use the port for NMI/KDB, and unmask_all_but_rx_interrupts after we're done with it.

The second option is obviously more complex, needlessly so, and less generic. So I went with the first one: we just consume all the interrupts. The tty becomes silently unusable for the rest of the world when we use it with KDB; but once we reroute the serial IRQ source back from NMI to an ordinary IRQ (in KDB this can be done with 'disable_nmi' command), it will behave as normal.

p.s. Since the callback is so far used only by polling users, we place it under the appropriate #ifdef.

Signed-off-by: Anton Vorontsov anton.vorontsov@linaro.org --- drivers/tty/serial/kgdboc.c | 10 ++++++++++ drivers/tty/serial/serial_core.c | 15 +++++++++++++++ include/linux/kgdb.h | 1 + include/linux/serial_core.h | 1 + include/linux/tty_driver.h | 1 + 5 files changed, 28 insertions(+)

diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c index 2b42a01..0aa08c8 100644 --- a/drivers/tty/serial/kgdboc.c +++ b/drivers/tty/serial/kgdboc.c @@ -227,6 +227,15 @@ static int kgdboc_get_char(void) kgdb_tty_line); }

+static void kgdboc_clear_irqs(void) +{ + if (!kgdb_tty_driver) + return; + if (kgdb_tty_driver->ops->clear_irqs) + kgdb_tty_driver->ops->clear_irqs(kgdb_tty_driver, + kgdb_tty_line); +} + static void kgdboc_put_char(u8 chr) { if (!kgdb_tty_driver) @@ -298,6 +307,7 @@ static struct kgdb_io kgdboc_io_ops = { .name = "kgdboc", .read_char = kgdboc_get_char, .write_char = kgdboc_put_char, + .clear_irqs = kgdboc_clear_irqs, .pre_exception = kgdboc_pre_exp_handler, .post_exception = kgdboc_post_exp_handler, }; diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index dcb2d5a..93c36cb 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -2187,6 +2187,20 @@ static void uart_poll_put_char(struct tty_driver *driver, int line, char ch) port = state->uart_port; port->ops->poll_put_char(port, ch); } + +static void uart_clear_irqs(struct tty_driver *driver, int line) +{ + struct uart_driver *drv = driver->driver_state; + struct uart_state *state = drv->state + line; + struct uart_port *port; + + if (!state || !state->uart_port) + return; + + port = state->uart_port; + if (port->ops->clear_irqs) + port->ops->clear_irqs(port); +} #endif

static const struct tty_operations uart_ops = { @@ -2219,6 +2233,7 @@ static const struct tty_operations uart_ops = { .poll_init = uart_poll_init, .poll_get_char = uart_poll_get_char, .poll_put_char = uart_poll_put_char, + .clear_irqs = uart_clear_irqs, #endif };

diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h index 3b111a6..1fd1cf0 100644 --- a/include/linux/kgdb.h +++ b/include/linux/kgdb.h @@ -295,6 +295,7 @@ struct kgdb_io { const char *name; int (*read_char) (void); void (*write_char) (u8); + void (*clear_irqs) (void); void (*flush) (void); int (*init) (void); void (*pre_exception) (void); diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h index 822c887..855fb6e 100644 --- a/include/linux/serial_core.h +++ b/include/linux/serial_core.h @@ -277,6 +277,7 @@ struct uart_ops { int (*poll_init)(struct uart_port *); void (*poll_put_char)(struct uart_port *, unsigned char); int (*poll_get_char)(struct uart_port *); + void (*clear_irqs)(struct uart_port *); #endif };

diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h index dd976cf..42f8a87 100644 --- a/include/linux/tty_driver.h +++ b/include/linux/tty_driver.h @@ -282,6 +282,7 @@ struct tty_operations { int (*poll_init)(struct tty_driver *driver, int line, char *options); int (*poll_get_char)(struct tty_driver *driver, int line); void (*poll_put_char)(struct tty_driver *driver, int line, char ch); + void (*clear_irqs)(struct tty_driver *driver, int line); #endif const struct file_operations *proc_fops; };

This special driver makes it possible to temporary use NMI debugger port as a normal console by issuing 'nmi_console' command (assuming that the port is attached to KGDB).

Unlike KDB's disable_nmi command, with this driver you are always able to go back to the debugger using KGDB escape sequence ($3#33). This is because this console driver processes the input in NMI context, and thus is able to intercept the magic sequence.

Note that since the console interprets input and uses polling communication methods, for things like PPP it is still better to fully detach debugger port from the KGDB NMI (i.e. disable_nmi), and use raw console.

Usually, to enter the debugger one have to type the magic sequence, so initially the kernel will print the following prompt on the NMI debugger console:

Type $3#33 to enter the debugger>

For convenience, there is a kgdb_fiq.knock kernel command line option, when set to 0, this turns the special command to just a return key press, so the kernel will be printing this:

Hit <return> to enter the debugger>

This is more convenient for long debugging sessions, although it makes nmi_console feature somewhat useless.

And for the cases when NMI connected to a dedicated button, the knocking can be disabled altogether by setting kgdb_fiq.knock to -1.

Suggested-by: Colin Cross ccross@android.com Signed-off-by: Anton Vorontsov anton.vorontsov@linaro.org --- drivers/tty/serial/Kconfig | 19 ++ drivers/tty/serial/Makefile | 1 + drivers/tty/serial/kgdb_nmi.c | 391 ++++++++++++++++++++++++++++++++++++++++++ drivers/tty/serial/kgdboc.c | 6 + include/linux/kgdb.h | 10 ++ 5 files changed, 427 insertions(+) create mode 100644 drivers/tty/serial/kgdb_nmi.c

diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig index 26907cf..b22e45b 100644 --- a/drivers/tty/serial/Kconfig +++ b/drivers/tty/serial/Kconfig @@ -141,6 +141,25 @@ config SERIAL_ATMEL_TTYAT

Say Y if you have an external 8250/16C550 UART. If unsure, say N.

+config SERIAL_KGDB_NMI + bool "Serial console over KGDB NMI debugger port" + depends on KGDB_SERIAL_CONSOLE + help + This special driver allows you to temporary use NMI debugger port + as a normal console (assuming that the port is attached to KGDB). + + Unlike KDB's disable_nmi command, with this driver you are always + able to go back to the debugger using KGDB escape sequence ($3#33). + This is because this console driver processes the input in NMI + context, and thus is able to intercept the magic sequence. + + Note that since the console interprets input and uses polling + communication methods, for things like PPP you still must fully + detach debugger port from the KGDB NMI (i.e. disable_nmi), and + use raw console. + + If unsure, say N. + config SERIAL_KS8695 bool "Micrel KS8695 (Centaur) serial port support" depends on ARCH_KS8695 diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile index ce88667..4f694da 100644 --- a/drivers/tty/serial/Makefile +++ b/drivers/tty/serial/Makefile @@ -61,6 +61,7 @@ obj-$(CONFIG_SERIAL_MSM_HS) += msm_serial_hs.o obj-$(CONFIG_SERIAL_NETX) += netx-serial.o obj-$(CONFIG_SERIAL_OF_PLATFORM) += of_serial.o obj-$(CONFIG_SERIAL_OF_PLATFORM_NWPSERIAL) += nwpserial.o +obj-$(CONFIG_SERIAL_KGDB_NMI) += kgdb_nmi.o obj-$(CONFIG_SERIAL_KS8695) += serial_ks8695.o obj-$(CONFIG_SERIAL_OMAP) += omap-serial.o obj-$(CONFIG_SERIAL_ALTERA_UART) += altera_uart.o diff --git a/drivers/tty/serial/kgdb_nmi.c b/drivers/tty/serial/kgdb_nmi.c new file mode 100644 index 0000000..fdb7d26 --- /dev/null +++ b/drivers/tty/serial/kgdb_nmi.c @@ -0,0 +1,391 @@ +/* + * 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 + * + * This program is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License version 2 as published + * by the Free Software Foundation. + */ + +#include <linux/kernel.h> +#include <linux/module.h> +#include <linux/compiler.h> +#include <linux/init.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/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 bool kgdb_nmi_tty_enabled; + +static void kgdb_nmi_console_write(struct console *co, const char *s, uint c) +{ + int i; + + if (!kgdb_nmi_tty_enabled || atomic_read(&kgdb_active) >= 0) + return; + + 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", + .write = kgdb_nmi_console_write, + .device = kgdb_nmi_console_device, + .flags = CON_PRINTBUFFER | CON_ANYTIME | CON_ENABLED, + .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; + int opened; + struct tasklet_struct tlet; + STRUCT_KFIFO(char, KGDB_NMI_FIFO_SIZE) fifo; +}; + +static struct kgdb_nmi_tty_priv *kgdb_nmi_port_to_priv(struct tty_port *port) +{ + return container_of(port, struct kgdb_nmi_tty_priv, port); +} + +/* + * Our debugging console is polled in a tasklet, so we'll check for input + * every tick. In HZ-less mode, we should program the next tick. We have + * to use the lowlevel stuff as no locks should be grabbed. + */ +#ifdef CONFIG_HIGH_RES_TIMERS +static void kgdb_tty_poke(void) +{ + tick_program_event(ktime_get(), 0); +} +#else +static inline void kgdb_tty_poke(void) {} +#endif + +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. Tasklet + * 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 = kgdb_nmi_port_to_priv(kgdb_nmi_port); + kfifo_in(&priv->fifo, &c, 1); + kgdb_tty_poke(); +} + +static int kgdb_nmi_poll_one_knock(void) +{ + static int n; + int c = -1; + const char *magic = kgdb_nmi_magic; + size_t m = strlen(magic); + bool printch = 0; + + 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 = 1; + } else { + n = 0; + } + + if (kgdb_nmi_tty_enabled) { + 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>", 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 1; + + dbg_io_ops->clear_irqs(); + + while (1) { + int ret; + + ret = kgdb_nmi_poll_one_knock(); + if (ret == NO_POLL_CHAR) + return 0; + else if (ret == 1) + break; + } + return 1; +} + +/* + * 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(unsigned long data) +{ + struct kgdb_nmi_tty_priv *priv = (void *)data; + struct tty_struct *tty; + char ch; + + tasklet_schedule(&priv->tlet); + + if (likely(!kgdb_nmi_tty_enabled || !kfifo_len(&priv->fifo))) + return; + + /* Port is there, but tty might be hung up, check. */ + tty = tty_port_tty_get(kgdb_nmi_port); + if (!tty) + return; + + while (kfifo_out(&priv->fifo, &ch, 1)) + tty_insert_flip_char(priv->port.tty, ch, TTY_NORMAL); + tty_flip_buffer_push(priv->port.tty); + + tty_kref_put(tty); +} + +static int kgdb_nmi_tty_activate(struct tty_port *port, struct tty_struct *tty) +{ + struct kgdb_nmi_tty_priv *priv = tty->driver_data; + + kgdb_nmi_port = port; + tasklet_schedule(&priv->tlet); + return 0; +} + +static void kgdb_nmi_tty_shutdown(struct tty_port *port) +{ + struct kgdb_nmi_tty_priv *priv = port->tty->driver_data; + + tasklet_kill(&priv->tlet); + 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); + tasklet_init(&priv->tlet, kgdb_nmi_tty_receiver, (unsigned long)priv); + 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 nstall tty port: %d\n", __func__, ret); + goto err; + } + return 0; +err: + 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; + kfree(priv); +} + +static int kgdb_nmi_tty_open(struct tty_struct *tty, struct file *file) +{ + struct kgdb_nmi_tty_priv *priv = tty->driver_data; + + return tty_port_open(&priv->port, tty, file); +} + +static void kgdb_nmi_tty_close(struct tty_struct *tty, struct file *file) +{ + struct kgdb_nmi_tty_priv *priv = tty->driver_data; + + tty_port_close(&priv->port, tty, file); +} + +static int kgdb_nmi_tty_write_room(struct tty_struct *tty) +{ + /* Actually, we can handle any amount as we use polled writes. */ + return 2048; +} + +static int kgdb_nmi_tty_write(struct tty_struct *tty, const unchar *buf, int 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, + .write_room = kgdb_nmi_tty_write_room, + .write = kgdb_nmi_tty_write, +}; + +static int kgdb_nmi_enable_console(int argc, const char *argv[]) +{ + kgdb_nmi_tty_enabled = !(argc == 1 && !strcmp(argv[1], "off")); + return 0; +} + +int kgdb_register_nmi_console(void) +{ + int ret; + + kgdb_nmi_tty_driver = alloc_tty_driver(1); + if (!kgdb_nmi_tty_driver) { + pr_err("%s: cannot allocate tty\n", __func__); + return -ENOMEM; + } + 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->flags = TTY_DRIVER_REAL_RAW; + 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; + } + + ret = kdb_register("nmi_console", kgdb_nmi_enable_console, "[off]", + "switch to Linux NMI console", 0); + if (ret) { + pr_err("%s: can't register kdb command: %d\n", __func__, ret); + goto err_kdb_reg; + } + + register_console(&kgdb_nmi_console); + kgdb_enable_nmi(1); + + return 0; +err_kdb_reg: + tty_unregister_driver(kgdb_nmi_tty_driver); +err_drv_reg: + put_tty_driver(kgdb_nmi_tty_driver); + return ret; +} +EXPORT_SYMBOL_GPL(kgdb_register_nmi_console); + +int kgdb_unregister_nmi_console(void) +{ + int ret; + + kgdb_enable_nmi(0); + kdb_unregister("nmi_console"); + + ret = unregister_console(&kgdb_nmi_console); + if (ret) + return ret; + + ret = tty_unregister_driver(kgdb_nmi_tty_driver); + if (ret) + return ret; + put_tty_driver(kgdb_nmi_tty_driver); + + return 0; +} +EXPORT_SYMBOL_GPL(kgdb_unregister_nmi_console); diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c index 0aa08c8..bb69803 100644 --- a/drivers/tty/serial/kgdboc.c +++ b/drivers/tty/serial/kgdboc.c @@ -145,6 +145,8 @@ __setup("kgdboc=", kgdboc_option_setup);

static void cleanup_kgdboc(void) { + if (kgdb_unregister_nmi_console()) + return; kgdboc_unregister_kbd(); if (configured == 1) kgdb_unregister_io_module(&kgdboc_io_ops); @@ -198,6 +200,10 @@ do_register: if (err) goto noconfig;

+ err = kgdb_register_nmi_console(); + if (err) + goto noconfig; + configured = 1;

return 0; diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h index 1fd1cf0..fb7c55c 100644 --- a/include/linux/kgdb.h +++ b/include/linux/kgdb.h @@ -245,6 +245,16 @@ extern void kgdb_arch_enable_nmi(bool on); */ extern int kgdb_enable_nmi(bool on);

+#ifdef CONFIG_SERIAL_KGDB_NMI +extern int kgdb_register_nmi_console(void); +extern int kgdb_unregister_nmi_console(void); +extern bool kgdb_nmi_poll_knock(void); +#else +static inline int kgdb_register_nmi_console(void) { return 0; } +static inline int kgdb_unregister_nmi_console(void) { return 0; } +static inline bool kgdb_nmi_poll_knock(void) { return 1; } +#endif + /** * struct kgdb_arch - Describe architecture specific values. * @gdb_bpt_instr: The instruction to trigger a breakpoint.

The FIQ debugger may be used to debug situations when the kernel stuck in uninterruptable sections, e.g. the kernel infinitely loops or deadlocked in an interrupt or with interrupts disabled.

By default KGDB FIQ is disabled in runtime, but can be enabled with kgdb_fiq.enable=1 kernel command line option.

Signed-off-by: Anton Vorontsov anton.vorontsov@linaro.org --- arch/arm/Kconfig | 18 ++++++++ arch/arm/include/asm/kgdb.h | 8 ++++ arch/arm/kernel/Makefile | 1 + arch/arm/kernel/kgdb_fiq.c | 99 ++++++++++++++++++++++++++++++++++++++++ arch/arm/kernel/kgdb_fiq_entry.S | 87 +++++++++++++++++++++++++++++++++++ 5 files changed, 213 insertions(+) create mode 100644 arch/arm/kernel/kgdb_fiq.c create mode 100644 arch/arm/kernel/kgdb_fiq_entry.S

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 6d6e18f..c978c74 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -171,6 +171,24 @@ config GENERIC_ISA_DMA config FIQ bool

+config ARCH_MIGHT_HAVE_KGDB_FIQ + bool + +config KGDB_FIQ + bool "KGDB/KDB FIQ debugger" + depends on KGDB_KDB && ARCH_MIGHT_HAVE_KGDB_FIQ && !THUMB2_KERNEL + select FIQ + help + The FIQ debugger may be used to debug situations when the + kernel stuck in uninterruptable sections, e.g. the kernel + infinitely loops or deadlocked in an interrupt or with + interrupts disabled. + + By default KGDB FIQ is disabled in runtime, but can be + enabled with kgdb_fiq.enable=1 kernel command line option. + + If unsure, say N. + config NEED_RET_TO_USER bool

diff --git a/arch/arm/include/asm/kgdb.h b/arch/arm/include/asm/kgdb.h index 48066ce..807e547 100644 --- a/arch/arm/include/asm/kgdb.h +++ b/arch/arm/include/asm/kgdb.h @@ -11,6 +11,8 @@ #define __ARM_KGDB_H__

#include <linux/ptrace.h> +#include <linux/linkage.h> +#include <asm/exception.h>

/* * GDB assumes that we're a user process being debugged, so @@ -47,6 +49,12 @@ static inline void arch_kgdb_breakpoint(void) extern void kgdb_handle_bus_error(void); extern int kgdb_fault_expected;

+extern char kgdb_fiq_handler; +extern char kgdb_fiq_handler_end; +asmlinkage void __exception_irq_entry kgdb_fiq_do_handle(struct pt_regs *regs); +extern int __init kgdb_register_fiq(unsigned int mach_kgdb_fiq, + void (*mach_kgdb_enable_fiq)(unsigned int irq, bool on), + bool (*mach_is_kgdb_fiq)(unsigned int irq)); #endif /* !__ASSEMBLY__ */

/* diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile index 7ad2d5c..5aa079b 100644 --- a/arch/arm/kernel/Makefile +++ b/arch/arm/kernel/Makefile @@ -56,6 +56,7 @@ obj-$(CONFIG_ATAGS_PROC) += atags.o obj-$(CONFIG_OABI_COMPAT) += sys_oabi-compat.o obj-$(CONFIG_ARM_THUMBEE) += thumbee.o obj-$(CONFIG_KGDB) += kgdb.o +obj-$(CONFIG_KGDB_FIQ) += kgdb_fiq_entry.o kgdb_fiq.o obj-$(CONFIG_ARM_UNWIND) += unwind.o obj-$(CONFIG_HAVE_TCM) += tcm.o obj-$(CONFIG_OF) += devtree.o diff --git a/arch/arm/kernel/kgdb_fiq.c b/arch/arm/kernel/kgdb_fiq.c new file mode 100644 index 0000000..8443af1 --- /dev/null +++ b/arch/arm/kernel/kgdb_fiq.c @@ -0,0 +1,99 @@ +/* + * KGDB FIQ + * + * Copyright 2010 Google, Inc. + * Arve Hjønnevåg arve@android.com + * Colin Cross ccross@android.com + * Copyright 2012 Linaro Ltd. + * Anton Vorontsov anton.vorontsov@linaro.org + * + * This program is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License version 2 as published + * by the Free Software Foundation. + */ + +#include <linux/kernel.h> +#include <linux/module.h> +#include <linux/init.h> +#include <linux/slab.h> +#include <linux/errno.h> +#include <linux/hardirq.h> +#include <linux/kdb.h> +#include <linux/kgdb.h> +#include <asm/fiq.h> +#include <asm/exception.h> + +static int kgdb_fiq_enabled; +module_param_named(enable, kgdb_fiq_enabled, int, 0600); +MODULE_PARM_DESC(enable, "set to 1 to enable FIQ KGDB"); + +static unsigned int kgdb_fiq; +static bool (*is_kgdb_fiq)(unsigned int irq); + +asmlinkage void __exception_irq_entry kgdb_fiq_do_handle(struct pt_regs *regs) +{ + if (!is_kgdb_fiq(kgdb_fiq)) + return; + if (!kgdb_nmi_poll_knock()) + return; + + nmi_enter(); + kgdb_handle_exception(1, 0, 0, regs); + nmi_exit(); +} + +static struct fiq_handler kgdb_fiq_desc = { + .name = "kgdb", +}; + +static long kgdb_fiq_setup_stack(void *info) +{ + struct pt_regs regs; + + regs.ARM_sp = __get_free_pages(GFP_KERNEL, THREAD_SIZE_ORDER) + + THREAD_START_SP; + WARN_ON(!regs.ARM_sp); + + set_fiq_regs(&regs); + return 0; +} + +static void (*kgdb_enable_fiq)(unsigned int irq, bool on); + +void kgdb_arch_enable_nmi(bool on) +{ + if (!kgdb_enable_fiq) + return; + kgdb_enable_fiq(kgdb_fiq, on); +} + +int __init kgdb_register_fiq(unsigned int mach_kgdb_fiq, + void (*mach_kgdb_enable_fiq)(unsigned int irq, bool on), + bool (*mach_is_kgdb_fiq)(unsigned int irq)) +{ + int err; + int cpu; + + if (!kgdb_fiq_enabled) + return -ENODEV; + if (kgdb_fiq) + return -EBUSY; + + kgdb_fiq = mach_kgdb_fiq; + kgdb_enable_fiq = mach_kgdb_enable_fiq; + is_kgdb_fiq = mach_is_kgdb_fiq; + + err = claim_fiq(&kgdb_fiq_desc); + if (err) { + pr_warn("%s: unable to claim fiq", __func__); + return err; + } + + for_each_possible_cpu(cpu) + work_on_cpu(cpu, kgdb_fiq_setup_stack, NULL); + + set_fiq_handler(&kgdb_fiq_handler, + &kgdb_fiq_handler_end - &kgdb_fiq_handler); + + return 0; +} diff --git a/arch/arm/kernel/kgdb_fiq_entry.S b/arch/arm/kernel/kgdb_fiq_entry.S new file mode 100644 index 0000000..d6becca --- /dev/null +++ b/arch/arm/kernel/kgdb_fiq_entry.S @@ -0,0 +1,87 @@ +/* + * KGDB FIQ entry + * + * Copyright 1996,1997,1998 Russell King. + * Copyright 2012 Linaro Ltd. + * Anton Vorontsov anton.vorontsov@linaro.org + * + * This program is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License version 2 as published + * by the Free Software Foundation. + */ + +#include <linux/linkage.h> +#include <asm/assembler.h> +#include <asm/memory.h> +#include <asm/unwind.h> +#include "entry-header.S" + + .text + +@ This is needed for usr_entry/alignment_trap +.LCcralign: + .long cr_alignment +.LCdohandle: + .long kgdb_fiq_do_handle + + .macro fiq_handler + ldr r1, =.LCdohandle + mov r0, sp + adr lr, BSYM(9997f) + ldr pc, [r1] +9997: + .endm + + .align 5 +__fiq_svc: + svc_entry + fiq_handler + mov r0, sp + ldmib r0, {r1 - r14} + msr cpsr_c, #FIQ_MODE | PSR_I_BIT | PSR_F_BIT + add r8, r0, #S_PC + ldr r9, [r0, #S_PSR] + msr spsr_cxsf, r9 + ldr r0, [r0, #S_R0] + ldmia r8, {pc}^ + + UNWIND(.fnend ) +ENDPROC(__fiq_svc) + .ltorg + + .align 5 +__fiq_usr: + usr_entry + kuser_cmpxchg_check + fiq_handler + get_thread_info tsk + mov why, #0 + b ret_to_user_from_irq + UNWIND(.fnend ) +ENDPROC(__fiq_usr) + .ltorg + + .global kgdb_fiq_handler +kgdb_fiq_handler: + + vector_stub fiq, FIQ_MODE, 4 + + .long __fiq_usr @ 0 (USR_26 / USR_32) + .long __fiq_svc @ 1 (FIQ_26 / FIQ_32) + .long __fiq_svc @ 2 (IRQ_26 / IRQ_32) + .long __fiq_svc @ 3 (SVC_26 / SVC_32) + .long __fiq_svc @ 4 + .long __fiq_svc @ 5 + .long __fiq_svc @ 6 + .long __fiq_svc @ 7 + .long __fiq_svc @ 8 + .long __fiq_svc @ 9 + .long __fiq_svc @ a + .long __fiq_svc @ b + .long __fiq_svc @ c + .long __fiq_svc @ d + .long __fiq_svc @ e + .long __fiq_svc @ f + + .global kgdb_fiq_handler_end +kgdb_fiq_handler_end:

If enabled, kernel will able to enter KGDB upon serial line activity on UART ports.

Note that even with this patch and CONFIG_KGDB_FIQ is enabled, you still need to pass kgdb_fiq.enable=1 kernel command line option, otherwise UART will behave in a normal way.

By default UART0 is used, but this can be changed via kgdb_fiq.uart_num kernel command line option.

Signed-off-by: Anton Vorontsov anton.vorontsov@linaro.org --- arch/arm/Kconfig | 1 + arch/arm/mach-versatile/Makefile | 1 + arch/arm/mach-versatile/kgdb_fiq.c | 31 +++++++++++++++++++++++++++++++ 3 files changed, 33 insertions(+) create mode 100644 arch/arm/mach-versatile/kgdb_fiq.c

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index c978c74..1a9881a 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -336,6 +336,7 @@ config ARCH_VERSATILE select PLAT_VERSATILE_CLCD select PLAT_VERSATILE_FPGA_IRQ select ARM_TIMER_SP804 + select ARCH_MIGHT_HAVE_KGDB_FIQ help This enables support for ARM Ltd Versatile board.

diff --git a/arch/arm/mach-versatile/Makefile b/arch/arm/mach-versatile/Makefile index 81fa3fe..bfd761f 100644 --- a/arch/arm/mach-versatile/Makefile +++ b/arch/arm/mach-versatile/Makefile @@ -7,3 +7,4 @@ obj-$(CONFIG_ARCH_VERSATILE_PB) += versatile_pb.o obj-$(CONFIG_MACH_VERSATILE_AB) += versatile_ab.o obj-$(CONFIG_MACH_VERSATILE_DT) += versatile_dt.o obj-$(CONFIG_PCI) += pci.o +obj-$(CONFIG_KGDB_FIQ) += kgdb_fiq.o diff --git a/arch/arm/mach-versatile/kgdb_fiq.c b/arch/arm/mach-versatile/kgdb_fiq.c new file mode 100644 index 0000000..3cdf71d --- /dev/null +++ b/arch/arm/mach-versatile/kgdb_fiq.c @@ -0,0 +1,31 @@ +/* + * KGDB FIQ board support + * + * Copyright 2012 Linaro Ltd. + * Anton Vorontsov anton.vorontsov@linaro.org + * + * This program is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License version 2 as published + * by the Free Software Foundation. + */ + +#include <linux/module.h> +#include <linux/init.h> +#include <linux/kgdb.h> +#include <mach/hardware.h> +#include <mach/platform.h> +#include <asm/hardware/vic.h> + +static int kgdb_fiq; +module_param_named(uart_num, kgdb_fiq, int, 0600); +MODULE_PARM_DESC(uart_num, "UART<number> port to use for KGDB FIQ"); + +static int __init kgdb_fiq_init(void) +{ + WARN_ON(kgdb_fiq > INT_UARTINT2 - INT_UARTINT0); + + return kgdb_register_fiq(INT_UARTINT0 + kgdb_fiq, + vic_fiq_select, + vic_is_fiq_rised); +} +console_initcall(kgdb_fiq_init);