Initial import

1 files changed, 1112 insertions, 0 deletions

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
new file mode 100644
index 000000000..9ffdfcf2e
--- /dev/null
+++ b/drivers/tty/sysrq.c
@@ -0,0 +1,1112 @@
+/*
+ *	Linux Magic System Request Key Hacks
+ *
+ *	(c) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz>
+ *	based on ideas by Pavel Machek <pavel@atrey.karlin.mff.cuni.cz>
+ *
+ *	(c) 2000 Crutcher Dunnavant <crutcher+kernel@datastacks.com>
+ *	overhauled to use key registration
+ *	based upon discusions in irc://irc.openprojects.net/#kernelnewbies
+ *
+ *	Copyright (c) 2010 Dmitry Torokhov
+ *	Input handler conversion
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/sched.h>
+#include <linux/sched/rt.h>
+#include <linux/interrupt.h>
+#include <linux/mm.h>
+#include <linux/fs.h>
+#include <linux/mount.h>
+#include <linux/kdev_t.h>
+#include <linux/major.h>
+#include <linux/reboot.h>
+#include <linux/sysrq.h>
+#include <linux/kbd_kern.h>
+#include <linux/proc_fs.h>
+#include <linux/nmi.h>
+#include <linux/quotaops.h>
+#include <linux/perf_event.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/suspend.h>
+#include <linux/writeback.h>
+#include <linux/swap.h>
+#include <linux/spinlock.h>
+#include <linux/vt_kern.h>
+#include <linux/workqueue.h>
+#include <linux/hrtimer.h>
+#include <linux/oom.h>
+#include <linux/slab.h>
+#include <linux/input.h>
+#include <linux/uaccess.h>
+#include <linux/moduleparam.h>
+#include <linux/jiffies.h>
+#include <linux/syscalls.h>
+#include <linux/of.h>
+#include <linux/rcupdate.h>
+
+#include <asm/ptrace.h>
+#include <asm/irq_regs.h>
+
+/* Whether we react on sysrq keys or just ignore them */
+static int __read_mostly sysrq_enabled = CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE;
+static bool __read_mostly sysrq_always_enabled;
+
+static bool sysrq_on(void)
+{
+	return sysrq_enabled || sysrq_always_enabled;
+}
+
+/*
+ * A value of 1 means 'all', other nonzero values are an op mask:
+ */
+static bool sysrq_on_mask(int mask)
+{
+	return sysrq_always_enabled ||
+	       sysrq_enabled == 1 ||
+	       (sysrq_enabled & mask);
+}
+
+static int __init sysrq_always_enabled_setup(char *str)
+{
+	sysrq_always_enabled = true;
+	pr_info("sysrq always enabled.\n");
+
+	return 1;
+}
+
+__setup("sysrq_always_enabled", sysrq_always_enabled_setup);
+
+
+static void sysrq_handle_loglevel(int key)
+{
+	int i;
+
+	i = key - '0';
+	console_loglevel = CONSOLE_LOGLEVEL_DEFAULT;
+	pr_info("Loglevel set to %d\n", i);
+	console_loglevel = i;
+}
+static struct sysrq_key_op sysrq_loglevel_op = {
+	.handler	= sysrq_handle_loglevel,
+	.help_msg	= "loglevel(0-9)",
+	.action_msg	= "Changing Loglevel",
+	.enable_mask	= SYSRQ_ENABLE_LOG,
+};
+
+#ifdef CONFIG_VT
+static void sysrq_handle_SAK(int key)
+{
+	struct work_struct *SAK_work = &vc_cons[fg_console].SAK_work;
+	schedule_work(SAK_work);
+}
+static struct sysrq_key_op sysrq_SAK_op = {
+	.handler	= sysrq_handle_SAK,
+	.help_msg	= "sak(k)",
+	.action_msg	= "SAK",
+	.enable_mask	= SYSRQ_ENABLE_KEYBOARD,
+};
+#else
+#define sysrq_SAK_op (*(struct sysrq_key_op *)NULL)
+#endif
+
+#ifdef CONFIG_VT
+static void sysrq_handle_unraw(int key)
+{
+	vt_reset_unicode(fg_console);
+}
+
+static struct sysrq_key_op sysrq_unraw_op = {
+	.handler	= sysrq_handle_unraw,
+	.help_msg	= "unraw(r)",
+	.action_msg	= "Keyboard mode set to system default",
+	.enable_mask	= SYSRQ_ENABLE_KEYBOARD,
+};
+#else
+#define sysrq_unraw_op (*(struct sysrq_key_op *)NULL)
+#endif /* CONFIG_VT */
+
+static void sysrq_handle_crash(int key)
+{
+	char *killer = NULL;
+
+	panic_on_oops = 1;	/* force panic */
+	wmb();
+	*killer = 1;
+}
+static struct sysrq_key_op sysrq_crash_op = {
+	.handler	= sysrq_handle_crash,
+	.help_msg	= "crash(c)",
+	.action_msg	= "Trigger a crash",
+	.enable_mask	= SYSRQ_ENABLE_DUMP,
+};
+
+static void sysrq_handle_reboot(int key)
+{
+	lockdep_off();
+	local_irq_enable();
+	emergency_restart();
+}
+static struct sysrq_key_op sysrq_reboot_op = {
+	.handler	= sysrq_handle_reboot,
+	.help_msg	= "reboot(b)",
+	.action_msg	= "Resetting",
+	.enable_mask	= SYSRQ_ENABLE_BOOT,
+};
+
+static void sysrq_handle_sync(int key)
+{
+	emergency_sync();
+}
+static struct sysrq_key_op sysrq_sync_op = {
+	.handler	= sysrq_handle_sync,
+	.help_msg	= "sync(s)",
+	.action_msg	= "Emergency Sync",
+	.enable_mask	= SYSRQ_ENABLE_SYNC,
+};
+
+static void sysrq_handle_show_timers(int key)
+{
+	sysrq_timer_list_show();
+}
+
+static struct sysrq_key_op sysrq_show_timers_op = {
+	.handler	= sysrq_handle_show_timers,
+	.help_msg	= "show-all-timers(q)",
+	.action_msg	= "Show clockevent devices & pending hrtimers (no others)",
+};
+
+static void sysrq_handle_mountro(int key)
+{
+	emergency_remount();
+}
+static struct sysrq_key_op sysrq_mountro_op = {
+	.handler	= sysrq_handle_mountro,
+	.help_msg	= "unmount(u)",
+	.action_msg	= "Emergency Remount R/O",
+	.enable_mask	= SYSRQ_ENABLE_REMOUNT,
+};
+
+#ifdef CONFIG_LOCKDEP
+static void sysrq_handle_showlocks(int key)
+{
+	debug_show_all_locks();
+}
+
+static struct sysrq_key_op sysrq_showlocks_op = {
+	.handler	= sysrq_handle_showlocks,
+	.help_msg	= "show-all-locks(d)",
+	.action_msg	= "Show Locks Held",
+};
+#else
+#define sysrq_showlocks_op (*(struct sysrq_key_op *)NULL)
+#endif
+
+#ifdef CONFIG_SMP
+static DEFINE_SPINLOCK(show_lock);
+
+static void showacpu(void *dummy)
+{
+	unsigned long flags;
+
+	/* Idle CPUs have no interesting backtrace. */
+	if (idle_cpu(smp_processor_id()))
+		return;
+
+	spin_lock_irqsave(&show_lock, flags);
+	pr_info("CPU%d:\n", smp_processor_id());
+	show_stack(NULL, NULL);
+	spin_unlock_irqrestore(&show_lock, flags);
+}
+
+static void sysrq_showregs_othercpus(struct work_struct *dummy)
+{
+	smp_call_function(showacpu, NULL, 0);
+}
+
+static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus);
+
+static void sysrq_handle_showallcpus(int key)
+{
+	/*
+	 * Fall back to the workqueue based printing if the
+	 * backtrace printing did not succeed or the
+	 * architecture has no support for it:
+	 */
+	if (!trigger_all_cpu_backtrace()) {
+		struct pt_regs *regs = get_irq_regs();
+
+		if (regs) {
+			pr_info("CPU%d:\n", smp_processor_id());
+			show_regs(regs);
+		}
+		schedule_work(&sysrq_showallcpus);
+	}
+}
+
+static struct sysrq_key_op sysrq_showallcpus_op = {
+	.handler	= sysrq_handle_showallcpus,
+	.help_msg	= "show-backtrace-all-active-cpus(l)",
+	.action_msg	= "Show backtrace of all active CPUs",
+	.enable_mask	= SYSRQ_ENABLE_DUMP,
+};
+#endif
+
+static void sysrq_handle_showregs(int key)
+{
+	struct pt_regs *regs = get_irq_regs();
+	if (regs)
+		show_regs(regs);
+	perf_event_print_debug();
+}
+static struct sysrq_key_op sysrq_showregs_op = {
+	.handler	= sysrq_handle_showregs,
+	.help_msg	= "show-registers(p)",
+	.action_msg	= "Show Regs",
+	.enable_mask	= SYSRQ_ENABLE_DUMP,
+};
+
+static void sysrq_handle_showstate(int key)
+{
+	show_state();
+	show_workqueue_state();
+}
+static struct sysrq_key_op sysrq_showstate_op = {
+	.handler	= sysrq_handle_showstate,
+	.help_msg	= "show-task-states(t)",
+	.action_msg	= "Show State",
+	.enable_mask	= SYSRQ_ENABLE_DUMP,
+};
+
+static void sysrq_handle_showstate_blocked(int key)
+{
+	show_state_filter(TASK_UNINTERRUPTIBLE);
+}
+static struct sysrq_key_op sysrq_showstate_blocked_op = {
+	.handler	= sysrq_handle_showstate_blocked,
+	.help_msg	= "show-blocked-tasks(w)",
+	.action_msg	= "Show Blocked State",
+	.enable_mask	= SYSRQ_ENABLE_DUMP,
+};
+
+#ifdef CONFIG_TRACING
+#include <linux/ftrace.h>
+
+static void sysrq_ftrace_dump(int key)
+{
+	ftrace_dump(DUMP_ALL);
+}
+static struct sysrq_key_op sysrq_ftrace_dump_op = {
+	.handler	= sysrq_ftrace_dump,
+	.help_msg	= "dump-ftrace-buffer(z)",
+	.action_msg	= "Dump ftrace buffer",
+	.enable_mask	= SYSRQ_ENABLE_DUMP,
+};
+#else
+#define sysrq_ftrace_dump_op (*(struct sysrq_key_op *)NULL)
+#endif
+
+static void sysrq_handle_showmem(int key)
+{
+	show_mem(0);
+}
+static struct sysrq_key_op sysrq_showmem_op = {
+	.handler	= sysrq_handle_showmem,
+	.help_msg	= "show-memory-usage(m)",
+	.action_msg	= "Show Memory",
+	.enable_mask	= SYSRQ_ENABLE_DUMP,
+};
+
+/*
+ * Signal sysrq helper function.  Sends a signal to all user processes.
+ */
+static void send_sig_all(int sig)
+{
+	struct task_struct *p;
+
+	read_lock(&tasklist_lock);
+	for_each_process(p) {
+		if (p->flags & PF_KTHREAD)
+			continue;
+		if (is_global_init(p))
+			continue;
+
+		do_send_sig_info(sig, SEND_SIG_FORCED, p, true);
+	}
+	read_unlock(&tasklist_lock);
+}
+
+static void sysrq_handle_term(int key)
+{
+	send_sig_all(SIGTERM);
+	console_loglevel = CONSOLE_LOGLEVEL_DEBUG;
+}
+static struct sysrq_key_op sysrq_term_op = {
+	.handler	= sysrq_handle_term,
+	.help_msg	= "terminate-all-tasks(e)",
+	.action_msg	= "Terminate All Tasks",
+	.enable_mask	= SYSRQ_ENABLE_SIGNAL,
+};
+
+static void moom_callback(struct work_struct *ignored)
+{
+	if (!out_of_memory(node_zonelist(first_memory_node, GFP_KERNEL),
+			   GFP_KERNEL, 0, NULL, true))
+		pr_info("OOM request ignored because killer is disabled\n");
+}
+
+static DECLARE_WORK(moom_work, moom_callback);
+
+static void sysrq_handle_moom(int key)
+{
+	schedule_work(&moom_work);
+}
+static struct sysrq_key_op sysrq_moom_op = {
+	.handler	= sysrq_handle_moom,
+	.help_msg	= "memory-full-oom-kill(f)",
+	.action_msg	= "Manual OOM execution",
+	.enable_mask	= SYSRQ_ENABLE_SIGNAL,
+};
+
+#ifdef CONFIG_BLOCK
+static void sysrq_handle_thaw(int key)
+{
+	emergency_thaw_all();
+}
+static struct sysrq_key_op sysrq_thaw_op = {
+	.handler	= sysrq_handle_thaw,
+	.help_msg	= "thaw-filesystems(j)",
+	.action_msg	= "Emergency Thaw of all frozen filesystems",
+	.enable_mask	= SYSRQ_ENABLE_SIGNAL,
+};
+#endif
+
+static void sysrq_handle_kill(int key)
+{
+	send_sig_all(SIGKILL);
+	console_loglevel = CONSOLE_LOGLEVEL_DEBUG;
+}
+static struct sysrq_key_op sysrq_kill_op = {
+	.handler	= sysrq_handle_kill,
+	.help_msg	= "kill-all-tasks(i)",
+	.action_msg	= "Kill All Tasks",
+	.enable_mask	= SYSRQ_ENABLE_SIGNAL,
+};
+
+static void sysrq_handle_unrt(int key)
+{
+	normalize_rt_tasks();
+}
+static struct sysrq_key_op sysrq_unrt_op = {
+	.handler	= sysrq_handle_unrt,
+	.help_msg	= "nice-all-RT-tasks(n)",
+	.action_msg	= "Nice All RT Tasks",
+	.enable_mask	= SYSRQ_ENABLE_RTNICE,
+};
+
+/* Key Operations table and lock */
+static DEFINE_SPINLOCK(sysrq_key_table_lock);
+
+static struct sysrq_key_op *sysrq_key_table[36] = {
+	&sysrq_loglevel_op,		/* 0 */
+	&sysrq_loglevel_op,		/* 1 */
+	&sysrq_loglevel_op,		/* 2 */
+	&sysrq_loglevel_op,		/* 3 */
+	&sysrq_loglevel_op,		/* 4 */
+	&sysrq_loglevel_op,		/* 5 */
+	&sysrq_loglevel_op,		/* 6 */
+	&sysrq_loglevel_op,		/* 7 */
+	&sysrq_loglevel_op,		/* 8 */
+	&sysrq_loglevel_op,		/* 9 */
+
+	/*
+	 * a: Don't use for system provided sysrqs, it is handled specially on
+	 * sparc and will never arrive.
+	 */
+	NULL,				/* a */
+	&sysrq_reboot_op,		/* b */
+	&sysrq_crash_op,		/* c & ibm_emac driver debug */
+	&sysrq_showlocks_op,		/* d */
+	&sysrq_term_op,			/* e */
+	&sysrq_moom_op,			/* f */
+	/* g: May be registered for the kernel debugger */
+	NULL,				/* g */
+	NULL,				/* h - reserved for help */
+	&sysrq_kill_op,			/* i */
+#ifdef CONFIG_BLOCK
+	&sysrq_thaw_op,			/* j */
+#else
+	NULL,				/* j */
+#endif
+	&sysrq_SAK_op,			/* k */
+#ifdef CONFIG_SMP
+	&sysrq_showallcpus_op,		/* l */
+#else
+	NULL,				/* l */
+#endif
+	&sysrq_showmem_op,		/* m */
+	&sysrq_unrt_op,			/* n */
+	/* o: This will often be registered as 'Off' at init time */
+	NULL,				/* o */
+	&sysrq_showregs_op,		/* p */
+	&sysrq_show_timers_op,		/* q */
+	&sysrq_unraw_op,		/* r */
+	&sysrq_sync_op,			/* s */
+	&sysrq_showstate_op,		/* t */
+	&sysrq_mountro_op,		/* u */
+	/* v: May be registered for frame buffer console restore */
+	NULL,				/* v */
+	&sysrq_showstate_blocked_op,	/* w */
+	/* x: May be registered on ppc/powerpc for xmon */
+	/* x: May be registered on sparc64 for global PMU dump */
+	NULL,				/* x */
+	/* y: May be registered on sparc64 for global register dump */
+	NULL,				/* y */
+	&sysrq_ftrace_dump_op,		/* z */
+};
+
+/* key2index calculation, -1 on invalid index */
+static int sysrq_key_table_key2index(int key)
+{
+	int retval;
+
+	if ((key >= '0') && (key <= '9'))
+		retval = key - '0';
+	else if ((key >= 'a') && (key <= 'z'))
+		retval = key + 10 - 'a';
+	else
+		retval = -1;
+	return retval;
+}
+
+/*
+ * get and put functions for the table, exposed to modules.
+ */
+struct sysrq_key_op *__sysrq_get_key_op(int key)
+{
+        struct sysrq_key_op *op_p = NULL;
+        int i;
+
+	i = sysrq_key_table_key2index(key);
+	if (i != -1)
+	        op_p = sysrq_key_table[i];
+
+        return op_p;
+}
+
+static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p)
+{
+        int i = sysrq_key_table_key2index(key);
+
+        if (i != -1)
+                sysrq_key_table[i] = op_p;
+}
+
+void __handle_sysrq(int key, bool check_mask)
+{
+	struct sysrq_key_op *op_p;
+	int orig_log_level;
+	int i;
+
+	rcu_sysrq_start();
+	rcu_read_lock();
+	/*
+	 * Raise the apparent loglevel to maximum so that the sysrq header
+	 * is shown to provide the user with positive feedback.  We do not
+	 * simply emit this at KERN_EMERG as that would change message
+	 * routing in the consumers of /proc/kmsg.
+	 */
+	orig_log_level = console_loglevel;
+	console_loglevel = CONSOLE_LOGLEVEL_DEFAULT;
+	pr_info("SysRq : ");
+
+        op_p = __sysrq_get_key_op(key);
+        if (op_p) {
+		/*
+		 * Should we check for enabled operations (/proc/sysrq-trigger
+		 * should not) and is the invoked operation enabled?
+		 */
+		if (!check_mask || sysrq_on_mask(op_p->enable_mask)) {
+			pr_cont("%s\n", op_p->action_msg);
+			console_loglevel = orig_log_level;
+			op_p->handler(key);
+		} else {
+			pr_cont("This sysrq operation is disabled.\n");
+		}
+	} else {
+		pr_cont("HELP : ");
+		/* Only print the help msg once per handler */
+		for (i = 0; i < ARRAY_SIZE(sysrq_key_table); i++) {
+			if (sysrq_key_table[i]) {
+				int j;
+
+				for (j = 0; sysrq_key_table[i] !=
+						sysrq_key_table[j]; j++)
+					;
+				if (j != i)
+					continue;
+				pr_cont("%s ", sysrq_key_table[i]->help_msg);
+			}
+		}
+		pr_cont("\n");
+		console_loglevel = orig_log_level;
+	}
+	rcu_read_unlock();
+	rcu_sysrq_end();
+}
+
+void handle_sysrq(int key)
+{
+	if (sysrq_on())
+		__handle_sysrq(key, true);
+}
+EXPORT_SYMBOL(handle_sysrq);
+
+#ifdef CONFIG_INPUT
+static int sysrq_reset_downtime_ms;
+
+/* Simple translation table for the SysRq keys */
+static const unsigned char sysrq_xlate[KEY_CNT] =
+        "\000\0331234567890-=\177\t"                    /* 0x00 - 0x0f */
+        "qwertyuiop[]\r\000as"                          /* 0x10 - 0x1f */
+        "dfghjkl;'`\000\\zxcv"                          /* 0x20 - 0x2f */
+        "bnm,./\000*\000 \000\201\202\203\204\205"      /* 0x30 - 0x3f */
+        "\206\207\210\211\212\000\000789-456+1"         /* 0x40 - 0x4f */
+        "230\177\000\000\213\214\000\000\000\000\000\000\000\000\000\000" /* 0x50 - 0x5f */
+        "\r\000/";                                      /* 0x60 - 0x6f */
+
+struct sysrq_state {
+	struct input_handle handle;
+	struct work_struct reinject_work;
+	unsigned long key_down[BITS_TO_LONGS(KEY_CNT)];
+	unsigned int alt;
+	unsigned int alt_use;
+	bool active;
+	bool need_reinject;
+	bool reinjecting;
+
+	/* reset sequence handling */
+	bool reset_canceled;
+	bool reset_requested;
+	unsigned long reset_keybit[BITS_TO_LONGS(KEY_CNT)];
+	int reset_seq_len;
+	int reset_seq_cnt;
+	int reset_seq_version;
+	struct timer_list keyreset_timer;
+};
+
+#define SYSRQ_KEY_RESET_MAX	20 /* Should be plenty */
+static unsigned short sysrq_reset_seq[SYSRQ_KEY_RESET_MAX];
+static unsigned int sysrq_reset_seq_len;
+static unsigned int sysrq_reset_seq_version = 1;
+
+static void sysrq_parse_reset_sequence(struct sysrq_state *state)
+{
+	int i;
+	unsigned short key;
+
+	state->reset_seq_cnt = 0;
+
+	for (i = 0; i < sysrq_reset_seq_len; i++) {
+		key = sysrq_reset_seq[i];
+
+		if (key == KEY_RESERVED || key > KEY_MAX)
+			break;
+
+		__set_bit(key, state->reset_keybit);
+		state->reset_seq_len++;
+
+		if (test_bit(key, state->key_down))
+			state->reset_seq_cnt++;
+	}
+
+	/* Disable reset until old keys are not released */
+	state->reset_canceled = state->reset_seq_cnt != 0;
+
+	state->reset_seq_version = sysrq_reset_seq_version;
+}
+
+static void sysrq_do_reset(unsigned long _state)
+{
+	struct sysrq_state *state = (struct sysrq_state *) _state;
+
+	state->reset_requested = true;
+
+	sys_sync();
+	kernel_restart(NULL);
+}
+
+static void sysrq_handle_reset_request(struct sysrq_state *state)
+{
+	if (state->reset_requested)
+		__handle_sysrq(sysrq_xlate[KEY_B], false);
+
+	if (sysrq_reset_downtime_ms)
+		mod_timer(&state->keyreset_timer,
+			jiffies + msecs_to_jiffies(sysrq_reset_downtime_ms));
+	else
+		sysrq_do_reset((unsigned long)state);
+}
+
+static void sysrq_detect_reset_sequence(struct sysrq_state *state,
+					unsigned int code, int value)
+{
+	if (!test_bit(code, state->reset_keybit)) {
+		/*
+		 * Pressing any key _not_ in reset sequence cancels
+		 * the reset sequence.  Also cancelling the timer in
+		 * case additional keys were pressed after a reset
+		 * has been requested.
+		 */
+		if (value && state->reset_seq_cnt) {
+			state->reset_canceled = true;
+			del_timer(&state->keyreset_timer);
+		}
+	} else if (value == 0) {
+		/*
+		 * Key release - all keys in the reset sequence need
+		 * to be pressed and held for the reset timeout
+		 * to hold.
+		 */
+		del_timer(&state->keyreset_timer);
+
+		if (--state->reset_seq_cnt == 0)
+			state->reset_canceled = false;
+	} else if (value == 1) {
+		/* key press, not autorepeat */
+		if (++state->reset_seq_cnt == state->reset_seq_len &&
+		    !state->reset_canceled) {
+			sysrq_handle_reset_request(state);
+		}
+	}
+}
+
+#ifdef CONFIG_OF
+static void sysrq_of_get_keyreset_config(void)
+{
+	u32 key;
+	struct device_node *np;
+	struct property *prop;
+	const __be32 *p;
+
+	np = of_find_node_by_path("/chosen/linux,sysrq-reset-seq");
+	if (!np) {
+		pr_debug("No sysrq node found");
+		return;
+	}
+
+	/* Reset in case a __weak definition was present */
+	sysrq_reset_seq_len = 0;
+
+	of_property_for_each_u32(np, "keyset", prop, p, key) {
+		if (key == KEY_RESERVED || key > KEY_MAX ||
+		    sysrq_reset_seq_len == SYSRQ_KEY_RESET_MAX)
+			break;
+
+		sysrq_reset_seq[sysrq_reset_seq_len++] = (unsigned short)key;
+	}
+
+	/* Get reset timeout if any. */
+	of_property_read_u32(np, "timeout-ms", &sysrq_reset_downtime_ms);
+}
+#else
+static void sysrq_of_get_keyreset_config(void)
+{
+}
+#endif
+
+static void sysrq_reinject_alt_sysrq(struct work_struct *work)
+{
+	struct sysrq_state *sysrq =
+			container_of(work, struct sysrq_state, reinject_work);
+	struct input_handle *handle = &sysrq->handle;
+	unsigned int alt_code = sysrq->alt_use;
+
+	if (sysrq->need_reinject) {
+		/* we do not want the assignment to be reordered */
+		sysrq->reinjecting = true;
+		mb();
+
+		/* Simulate press and release of Alt + SysRq */
+		input_inject_event(handle, EV_KEY, alt_code, 1);
+		input_inject_event(handle, EV_KEY, KEY_SYSRQ, 1);
+		input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
+
+		input_inject_event(handle, EV_KEY, KEY_SYSRQ, 0);
+		input_inject_event(handle, EV_KEY, alt_code, 0);
+		input_inject_event(handle, EV_SYN, SYN_REPORT, 1);
+
+		mb();
+		sysrq->reinjecting = false;
+	}
+}
+
+static bool sysrq_handle_keypress(struct sysrq_state *sysrq,
+				  unsigned int code, int value)
+{
+	bool was_active = sysrq->active;
+	bool suppress;
+
+	switch (code) {
+
+	case KEY_LEFTALT:
+	case KEY_RIGHTALT:
+		if (!value) {
+			/* One of ALTs is being released */
+			if (sysrq->active && code == sysrq->alt_use)
+				sysrq->active = false;
+
+			sysrq->alt = KEY_RESERVED;
+
+		} else if (value != 2) {
+			sysrq->alt = code;
+			sysrq->need_reinject = false;
+		}
+		break;
+
+	case KEY_SYSRQ:
+		if (value == 1 && sysrq->alt != KEY_RESERVED) {
+			sysrq->active = true;
+			sysrq->alt_use = sysrq->alt;
+			/*
+			 * If nothing else will be pressed we'll need
+			 * to re-inject Alt-SysRq keysroke.
+			 */
+			sysrq->need_reinject = true;
+		}
+
+		/*
+		 * Pretend that sysrq was never pressed at all. This
+		 * is needed to properly handle KGDB which will try
+		 * to release all keys after exiting debugger. If we
+		 * do not clear key bit it KGDB will end up sending
+		 * release events for Alt and SysRq, potentially
+		 * triggering print screen function.
+		 */
+		if (sysrq->active)
+			clear_bit(KEY_SYSRQ, sysrq->handle.dev->key);
+
+		break;
+
+	default:
+		if (sysrq->active && value && value != 2) {
+			sysrq->need_reinject = false;
+			__handle_sysrq(sysrq_xlate[code], true);
+		}
+		break;
+	}
+
+	suppress = sysrq->active;
+
+	if (!sysrq->active) {
+
+		/*
+		 * See if reset sequence has changed since the last time.
+		 */
+		if (sysrq->reset_seq_version != sysrq_reset_seq_version)
+			sysrq_parse_reset_sequence(sysrq);
+
+		/*
+		 * If we are not suppressing key presses keep track of
+		 * keyboard state so we can release keys that have been
+		 * pressed before entering SysRq mode.
+		 */
+		if (value)
+			set_bit(code, sysrq->key_down);
+		else
+			clear_bit(code, sysrq->key_down);
+
+		if (was_active)
+			schedule_work(&sysrq->reinject_work);
+
+		/* Check for reset sequence */
+		sysrq_detect_reset_sequence(sysrq, code, value);
+
+	} else if (value == 0 && test_and_clear_bit(code, sysrq->key_down)) {
+		/*
+		 * Pass on release events for keys that was pressed before
+		 * entering SysRq mode.
+		 */
+		suppress = false;
+	}
+
+	return suppress;
+}
+
+static bool sysrq_filter(struct input_handle *handle,
+			 unsigned int type, unsigned int code, int value)
+{
+	struct sysrq_state *sysrq = handle->private;
+	bool suppress;
+
+	/*
+	 * Do not filter anything if we are in the process of re-injecting
+	 * Alt+SysRq combination.
+	 */
+	if (sysrq->reinjecting)
+		return false;
+
+	switch (type) {
+
+	case EV_SYN:
+		suppress = false;
+		break;
+
+	case EV_KEY:
+		suppress = sysrq_handle_keypress(sysrq, code, value);
+		break;
+
+	default:
+		suppress = sysrq->active;
+		break;
+	}
+
+	return suppress;
+}
+
+static int sysrq_connect(struct input_handler *handler,
+			 struct input_dev *dev,
+			 const struct input_device_id *id)
+{
+	struct sysrq_state *sysrq;
+	int error;
+
+	sysrq = kzalloc(sizeof(struct sysrq_state), GFP_KERNEL);
+	if (!sysrq)
+		return -ENOMEM;
+
+	INIT_WORK(&sysrq->reinject_work, sysrq_reinject_alt_sysrq);
+
+	sysrq->handle.dev = dev;
+	sysrq->handle.handler = handler;
+	sysrq->handle.name = "sysrq";
+	sysrq->handle.private = sysrq;
+	setup_timer(&sysrq->keyreset_timer,
+		    sysrq_do_reset, (unsigned long)sysrq);
+
+	error = input_register_handle(&sysrq->handle);
+	if (error) {
+		pr_err("Failed to register input sysrq handler, error %d\n",
+			error);
+		goto err_free;
+	}
+
+	error = input_open_device(&sysrq->handle);
+	if (error) {
+		pr_err("Failed to open input device, error %d\n", error);
+		goto err_unregister;
+	}
+
+	return 0;
+
+ err_unregister:
+	input_unregister_handle(&sysrq->handle);
+ err_free:
+	kfree(sysrq);
+	return error;
+}
+
+static void sysrq_disconnect(struct input_handle *handle)
+{
+	struct sysrq_state *sysrq = handle->private;
+
+	input_close_device(handle);
+	cancel_work_sync(&sysrq->reinject_work);
+	del_timer_sync(&sysrq->keyreset_timer);
+	input_unregister_handle(handle);
+	kfree(sysrq);
+}
+
+/*
+ * We are matching on KEY_LEFTALT instead of KEY_SYSRQ because not all
+ * keyboards have SysRq key predefined and so user may add it to keymap
+ * later, but we expect all such keyboards to have left alt.
+ */
+static const struct input_device_id sysrq_ids[] = {
+	{
+		.flags = INPUT_DEVICE_ID_MATCH_EVBIT |
+				INPUT_DEVICE_ID_MATCH_KEYBIT,
+		.evbit = { BIT_MASK(EV_KEY) },
+		.keybit = { BIT_MASK(KEY_LEFTALT) },
+	},
+	{ },
+};
+
+static struct input_handler sysrq_handler = {
+	.filter		= sysrq_filter,
+	.connect	= sysrq_connect,
+	.disconnect	= sysrq_disconnect,
+	.name		= "sysrq",
+	.id_table	= sysrq_ids,
+};
+
+static bool sysrq_handler_registered;
+
+static inline void sysrq_register_handler(void)
+{
+	int error;
+
+	sysrq_of_get_keyreset_config();
+
+	error = input_register_handler(&sysrq_handler);
+	if (error)
+		pr_err("Failed to register input handler, error %d", error);
+	else
+		sysrq_handler_registered = true;
+}
+
+static inline void sysrq_unregister_handler(void)
+{
+	if (sysrq_handler_registered) {
+		input_unregister_handler(&sysrq_handler);
+		sysrq_handler_registered = false;
+	}
+}
+
+static int sysrq_reset_seq_param_set(const char *buffer,
+				     const struct kernel_param *kp)
+{
+	unsigned long val;
+	int error;
+
+	error = kstrtoul(buffer, 0, &val);
+	if (error < 0)
+		return error;
+
+	if (val > KEY_MAX)
+		return -EINVAL;
+
+	*((unsigned short *)kp->arg) = val;
+	sysrq_reset_seq_version++;
+
+	return 0;
+}
+
+static struct kernel_param_ops param_ops_sysrq_reset_seq = {
+	.get	= param_get_ushort,
+	.set	= sysrq_reset_seq_param_set,
+};
+
+#define param_check_sysrq_reset_seq(name, p)	\
+	__param_check(name, p, unsigned short)
+
+module_param_array_named(reset_seq, sysrq_reset_seq, sysrq_reset_seq,
+			 &sysrq_reset_seq_len, 0644);
+
+module_param_named(sysrq_downtime_ms, sysrq_reset_downtime_ms, int, 0644);
+
+#else
+
+static inline void sysrq_register_handler(void)
+{
+}
+
+static inline void sysrq_unregister_handler(void)
+{
+}
+
+#endif /* CONFIG_INPUT */
+
+int sysrq_toggle_support(int enable_mask)
+{
+	bool was_enabled = sysrq_on();
+
+	sysrq_enabled = enable_mask;
+
+	if (was_enabled != sysrq_on()) {
+		if (sysrq_on())
+			sysrq_register_handler();
+		else
+			sysrq_unregister_handler();
+	}
+
+	return 0;
+}
+
+static int __sysrq_swap_key_ops(int key, struct sysrq_key_op *insert_op_p,
+                                struct sysrq_key_op *remove_op_p)
+{
+	int retval;
+
+	spin_lock(&sysrq_key_table_lock);
+	if (__sysrq_get_key_op(key) == remove_op_p) {
+		__sysrq_put_key_op(key, insert_op_p);
+		retval = 0;
+	} else {
+		retval = -1;
+	}
+	spin_unlock(&sysrq_key_table_lock);
+
+	/*
+	 * A concurrent __handle_sysrq either got the old op or the new op.
+	 * Wait for it to go away before returning, so the code for an old
+	 * op is not freed (eg. on module unload) while it is in use.
+	 */
+	synchronize_rcu();
+
+	return retval;
+}
+
+int register_sysrq_key(int key, struct sysrq_key_op *op_p)
+{
+	return __sysrq_swap_key_ops(key, op_p, NULL);
+}
+EXPORT_SYMBOL(register_sysrq_key);
+
+int unregister_sysrq_key(int key, struct sysrq_key_op *op_p)
+{
+	return __sysrq_swap_key_ops(key, NULL, op_p);
+}
+EXPORT_SYMBOL(unregister_sysrq_key);
+
+#ifdef CONFIG_PROC_FS
+/*
+ * writing 'C' to /proc/sysrq-trigger is like sysrq-C
+ */
+static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf,
+				   size_t count, loff_t *ppos)
+{
+	if (count) {
+		char c;
+
+		if (get_user(c, buf))
+			return -EFAULT;
+		__handle_sysrq(c, false);
+	}
+
+	return count;
+}
+
+static const struct file_operations proc_sysrq_trigger_operations = {
+	.write		= write_sysrq_trigger,
+	.llseek		= noop_llseek,
+};
+
+static void sysrq_init_procfs(void)
+{
+	if (!proc_create("sysrq-trigger", S_IWUSR, NULL,
+			 &proc_sysrq_trigger_operations))
+		pr_err("Failed to register proc interface\n");
+}
+
+#else
+
+static inline void sysrq_init_procfs(void)
+{
+}
+
+#endif /* CONFIG_PROC_FS */
+
+static int __init sysrq_init(void)
+{
+	sysrq_init_procfs();
+
+	if (sysrq_on())
+		sysrq_register_handler();
+
+	return 0;
+}
+module_init(sysrq_init);