kgdb: Infrastructure to request NMI handling

This addes code to the kgdb_nmi code to install an explicit NMI handler
using the polling infrastructure. Whilst doing this we simplify even
further the relationships between kgdb core, kgdboc and kgdb_nmi.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>

3 files changed, 55 insertions, 24 deletions

diff --git a/drivers/tty/serial/kgdb_nmi.c b/drivers/tty/serial/kgdb_nmi.c
index 129dc5be6028..1a6a4fb5e63c 100644
--- a/drivers/tty/serial/kgdb_nmi.c
+++ b/drivers/tty/serial/kgdb_nmi.c
@@ -29,6 +29,7 @@
 #include <linux/kfifo.h>
 #include <linux/kgdb.h>
 #include <linux/kdb.h>
+#include <linux/irq.h>
 
 static int kgdb_nmi_knock = 1;
 module_param_named(knock, kgdb_nmi_knock, int, 0600);
@@ -44,15 +45,12 @@ 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_set_enable(int enabled);
+
 static int kgdb_nmi_console_setup(struct console *co, char *options)
 {
-	arch_kgdb_ops.enable_nmi(1);
+	(void) kgdb_nmi_set_enable(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->is_console = true;
 
 	return 0;
@@ -157,7 +155,7 @@ static int kgdb_nmi_poll_one_knock(void)
 }
 
 /**
- * kgdb_nmi_poll_knock - Check if it is time to enter the debugger
+ * kgdb_handle_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
@@ -170,23 +168,42 @@ static int kgdb_nmi_poll_one_knock(void)
  * 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)
+static irqreturn_t kgdb_handle_nmi_poll_knock(int irq, void *unused)
 {
+	int ret = IRQ_NONE;
+
 	if (kgdb_nmi_knock < 0)
 		return 1;
 
 	while (1) {
-		int ret;
-
-		ret = kgdb_nmi_poll_one_knock();
-		if (ret == NO_POLL_CHAR)
-			return 0;
-		else if (ret == 1)
+		switch (kgdb_nmi_poll_one_knock()) {
+		case NO_POLL_CHAR:
+			return ret;
+		case 1:
+			kgdb_handle_exception(1, 0, 0, get_irq_regs());
+			return IRQ_HANDLED;
+		default:
+			ret = IRQ_HANDLED;
 			break;
+		}
 	}
-	return 1;
+
+	return IRQ_HANDLED;
 }
 
+static int kgdb_nmi_set_enable(int enabled)
+{
+	int res = 0;
+
+	if (enabled)
+		res = dbg_io_ops->request_nmi(kgdb_handle_nmi_poll_knock);
+	else
+		dbg_io_ops->free_nmi();
+
+	return res;
+}
+
+
 /*
  * The tasklet is cheap, it does not cause wakeups when reschedules itself,
  * instead it waits for the next tick.
@@ -330,9 +347,6 @@ int kgdb_register_nmi_console(void)
 {
 	int ret;
 
-	if (!arch_kgdb_ops.enable_nmi)
-		return 0;
-
 	kgdb_nmi_tty_driver = alloc_tty_driver(1);
 	if (!kgdb_nmi_tty_driver) {
 		pr_err("%s: cannot allocate tty\n", __func__);
@@ -368,10 +382,6 @@ 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;
diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index a260cde743e2..4cf5e0a8ede8 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -245,6 +245,24 @@ static void kgdboc_put_char(u8 chr)
 					kgdb_tty_line, chr);
 }
 
+static int kgdboc_request_nmi(irq_handler_t handler)
+{
+	if (!kgdb_tty_driver || !kgdb_tty_driver->ops->poll_request_nmi ||
+				!kgdb_tty_driver->ops->poll_free_nmi)
+		return -EINVAL;
+
+	return kgdb_tty_driver->ops->poll_request_nmi(kgdb_tty_driver,
+						      kgdb_tty_line, handler);
+}
+
+static void kgdboc_free_nmi(void)
+{
+	if (!kgdb_tty_driver)
+		return;
+	return kgdb_tty_driver->ops->poll_free_nmi(kgdb_tty_driver,
+						   kgdb_tty_line);
+}
+
 static int param_set_kgdboc_var(const char *kmessage, struct kernel_param *kp)
 {
 	int len = strlen(kmessage);
@@ -308,6 +326,8 @@ static struct kgdb_io kgdboc_io_ops = {
 	.name			= "kgdboc",
 	.read_char		= kgdboc_get_char,
 	.write_char		= kgdboc_put_char,
+	.request_nmi		= kgdboc_request_nmi,
+	.free_nmi		= kgdboc_free_nmi,
 	.pre_exception		= kgdboc_pre_exp_handler,
 	.post_exception		= kgdboc_post_exp_handler,
 };
diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
index e465bb15912d..0f01e28201a4 100644
--- a/include/linux/kgdb.h
+++ b/include/linux/kgdb.h
@@ -16,6 +16,7 @@
 #include <linux/linkage.h>
 #include <linux/init.h>
 #include <linux/atomic.h>
+#include <linux/interrupt.h>
 #ifdef CONFIG_HAVE_ARCH_KGDB
 #include <asm/kgdb.h>
 #endif
@@ -274,6 +275,8 @@ struct kgdb_io {
 	const char		*name;
 	int			(*read_char) (void);
 	void			(*write_char) (u8);
+	int			(*request_nmi) (irq_handler_t);
+	void			(*free_nmi) (void);
 	void			(*flush) (void);
 	int			(*init) (void);
 	void			(*pre_exception) (void);
@@ -288,11 +291,9 @@ extern unsigned long kgdb_arch_pc(int exception, struct pt_regs *regs);
 #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
 
 extern int kgdb_register_io_module(struct kgdb_io *local_kgdb_io_ops);