The ACPI DBG2 table defines a debug console. Add support for parsing it
and using it to select earlycon destination when no arguments provided.

Signed-off-by: Leif Lindholm <redacted>
---
 arch/arm64/kernel/acpi.c      |   2 +
 drivers/acpi/Makefile         |   1 +
 drivers/acpi/console.c        | 103 ++++++++++++++++++++++++++++++++++++++++++
 drivers/of/fdt.c              |   2 +-
 drivers/tty/serial/earlycon.c |  16 ++++---
 include/linux/acpi.h          |   4 ++
 include/linux/serial_core.h   |   9 ++--
 7 files changed, 126 insertions(+), 11 deletions(-)
 create mode 100644 drivers/acpi/console.c

diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
index b9a5623..be7600a 100644
--- a/arch/arm64/kernel/acpi.c
+++ b/arch/arm64/kernel/acpi.c

@@ -207,6 +207,8 @@ void __init acpi_boot_table_init(void)
 		if (!param_acpi_force)
 			disable_acpi();
 	}
+
+	acpi_early_console_probe();
 }
 
 void __init acpi_gic_init(void)

diff --git a/drivers/acpi/Makefile b/drivers/acpi/Makefile
index b5e7cd8..a89587d 100644
--- a/drivers/acpi/Makefile
+++ b/drivers/acpi/Makefile

@@ -10,6 +10,7 @@ ccflags-$(CONFIG_ACPI_DEBUG)	+= -DACPI_DEBUG_OUTPUT
 #
 obj-y				+= tables.o
 obj-$(CONFIG_X86)		+= blacklist.o
+obj-y				+= console.o

 
 #
 # ACPI Core Subsystem (Interpreter)

diff --git a/drivers/acpi/console.c b/drivers/acpi/console.c
new file mode 100644
index 0000000..a985890
--- /dev/null
+++ b/drivers/acpi/console.c

@@ -0,0 +1,103 @@
+/*
+ * Copyright (c) 2012, Intel Corporation
+ * Copyright (c) 2015, Linaro Ltd.
+ *
+ * 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.
+ *
+ */
+
+#define DEBUG
+#define pr_fmt(fmt) "ACPI: " KBUILD_MODNAME ": " fmt
+
+#include <linux/acpi.h>
+#include <linux/kernel.h>
+#include <linux/serial_core.h>
+
+#define NUM_ELEMS(x) (sizeof(x) / sizeof(*x))
+
+#ifdef CONFIG_SERIAL_EARLYCON
+static int use_earlycon __initdata;
+static int __init setup_acpi_earlycon(char *buf)
+{
+	if (!buf)
+		use_earlycon = 1;
+
+	return 0;
+}
+early_param("earlycon", setup_acpi_earlycon);
+
+extern struct earlycon_id __earlycon_table[];
+
+static __initdata struct {
+	int id;
+	const char *name;
+} subtypes[] = {
+	{0, "uart8250"},
+	{1, "uart8250"},
+	{2, NULL},
+	{3, "pl011"},
+};

+
+		entry = (struct acpi_dbg2_device *)
+			((void *)entry + entry->length);
+	}
+
+	return 0;
+}
+
+int __init acpi_early_console_probe(void)
+{
+	acpi_table_parse(ACPI_SIG_DBG2, acpi_parse_dbg2);
+
+	return 0;
+}
+#endif /* CONFIG_SERIAL_EARLYCON */

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index fcfc4c7..a96209f 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c

@@ -829,7 +829,7 @@ int __init early_init_dt_scan_chosen_serial(void)
 		if (!addr)
 			return -ENXIO;
 
-		of_setup_earlycon(addr, match->data);
+		setup_earlycon_driver(addr, match->data);
 		return 0;
 	}
 	return -ENODEV;

diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
index 2bda09a..c063cbb 100644
--- a/drivers/tty/serial/earlycon.c
+++ b/drivers/tty/serial/earlycon.c

@@ -13,6 +13,7 @@
 
 #define pr_fmt(fmt)	KBUILD_MODNAME ": " fmt
 
+#include <linux/acpi.h>
 #include <linux/console.h>
 #include <linux/kernel.h>
 #include <linux/init.h>

@@ -184,12 +185,16 @@ static int __init param_setup_earlycon(char *buf)
 	int err;
 
 	/*
-	 * Just 'earlycon' is a valid param for devicetree earlycons;
-	 * don't generate a warning from parse_early_params() in that case
+	 * Just 'earlycon' is a valid param for devicetree or ACPI earlycons;
+	 * ACPI cannot be parsed yet, so return without action if enabled.
+	 * Otherwise, attempt initialization using DT.
 	 */
-	if (!buf || !buf[0])
-		if (IS_ENABLED(CONFIG_OF_FLATTREE))
+	if (!buf || !buf[0]) {
+		if (!acpi_disabled)

+			return 0;
+		else if (IS_ENABLED(CONFIG_OF_FLATTREE))
 			return early_init_dt_scan_chosen_serial();
+	}
 
 	err = setup_earlycon(buf);
 	if (err == -ENOENT || err == -EALREADY)

@@ -198,8 +203,7 @@ static int __init param_setup_earlycon(char *buf)
 }
 early_param("earlycon", param_setup_earlycon);
 
-int __init of_setup_earlycon(unsigned long addr,
-			     int (*setup)(struct earlycon_device *, const char *))
+int __init setup_earlycon_driver(unsigned long addr, earlycon_initfunc_t setup)
 {
 	int err;
 	struct uart_port *port = &early_console_dev.port;

diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 7235c48..88cb9c1 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h

@@ -811,4 +811,8 @@ static inline struct acpi_device *acpi_get_next_child(struct device *dev,
 
 #endif
 
+#if defined(CONFIG_ACPI) && defined(CONFIG_SERIAL_EARLYCON)
+int __init acpi_early_console_probe(void);
+#endif
+
 #endif	/*_LINUX_ACPI_H*/

diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 297d4fa..39e99b0 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h

@@ -339,14 +339,15 @@ struct earlycon_device {
 	unsigned int baud;
 };
 
+typedef int (*earlycon_initfunc_t)(struct earlycon_device *, const char *);
+
 struct earlycon_id {
-	char	name[16];
-	int	(*setup)(struct earlycon_device *, const char *options);
+	char			name[16];
+	earlycon_initfunc_t	setup;
 } __aligned(32);
 
 extern int setup_earlycon(char *buf);
-extern int of_setup_earlycon(unsigned long addr,
-			     int (*setup)(struct earlycon_device *, const char *));
+extern int setup_earlycon_driver(unsigned long addr, earlycon_initfunc_t setup);
 
 #define EARLYCON_DECLARE(_name, func)					\
 	static const struct earlycon_id __earlycon_##_name		\