[PATCH 3/7] kgdb: Add request_nmi() to the io ops table for kgdboc

[Sumit Garg <sumit.garg@xxxxxxxxxx>]

From: Daniel Thompson <daniel.thompson@xxxxxxxxxx>

Add request_nmi() callback to install a non-maskable interrupt handler
corresponding to IRQ retrieved from polling interface. If NMI handler
installation fails due to missing support from underlying irqchip driver
then fallback to install it as normal interrupt handler.

Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Co-developed-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
Signed-off-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
---
 drivers/tty/serial/kgdboc.c | 35 +++++++++++++++++++++++++++++++++++
 include/linux/kgdb.h        |  7 +++++++
 2 files changed, 42 insertions(+)

diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
index 84ffede..263afae 100644
--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -19,6 +19,9 @@
 #include <linux/console.h>
 #include <linux/vt_kern.h>
 #include <linux/input.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/irqdesc.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/serial_core.h>
@@ -390,12 +393,44 @@ static void kgdboc_post_exp_handler(void)
 	kgdboc_restore_input();
 }
 
+static int kgdb_tty_irq;
+
+static int kgdboc_request_nmi(irq_handler_t fn, void *dev_id)
+{
+	int irq, res;
+
+	/* Better to avoid double allocation in the tty driver! */
+	if (kgdb_tty_irq)
+		return 0;
+
+	if (!kgdb_tty_driver->ops->poll_get_irq)
+		return -ENODEV;
+
+	irq =
+	    kgdb_tty_driver->ops->poll_get_irq(kgdb_tty_driver, kgdb_tty_line);
+	if (irq <= 0)
+		return irq ? irq : -ENODEV;
+
+	irq_set_status_flags(irq, IRQ_NOAUTOEN);
+	res = request_nmi(irq, fn, IRQF_PERCPU, "kgdboc", dev_id);
+	if (res) {
+		res = request_irq(irq, fn, IRQF_SHARED, "kgdboc", dev_id);
+		WARN_ON(res);
+	}
+
+	enable_irq(irq);
+
+	kgdb_tty_irq = irq;
+	return 0;
+}
+
 static struct kgdb_io kgdboc_io_ops = {
 	.name			= "kgdboc",
 	.read_char		= kgdboc_get_char,
 	.write_char		= kgdboc_put_char,
 	.pre_exception		= kgdboc_pre_exp_handler,
 	.post_exception		= kgdboc_post_exp_handler,
+	.request_nmi		= kgdboc_request_nmi,
 };
 
 #if IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE)
diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
index 529116b..b32b044 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
@@ -276,6 +277,10 @@ struct kgdb_arch {
  * the I/O driver.
  * @post_exception: Pointer to a function that will do any cleanup work
  * for the I/O driver.
+ * @request_nmi: Pointer to a function that can install an non-maskable
+ * interrupt handler that will be called when a character is pending and that
+ * can be cleared by calling @read_char until it returns NO_POLL_CHAR. If NMI
+ * installation fails then fallback to install normal interrupt handler.
  * @cons: valid if the I/O device is a console; else NULL.
  */
 struct kgdb_io {
@@ -287,6 +292,8 @@ struct kgdb_io {
 	void			(*deinit) (void);
 	void			(*pre_exception) (void);
 	void			(*post_exception) (void);
+	int			(*request_nmi)(irq_handler_t nmi_handler,
+					       void *dev_id);
 	struct console		*cons;
 };
 
-- 
2.7.4