From: Mark Salter <msalter@redhat.com>
Date: Wed, 25 Mar 2015 14:17:50 -0400
Subject: [PATCH] arm64: avoid needing console= to enable serial console

Tell kernel to prefer one of the serial ports for console on
platforms currently supported (pl011 or 8250). console= on
command line will override these assumed preferences. This is
just a hack to get the behavior we want from DT provided by
firmware.

Signed-off-by: Mark Salter <msalter@redhat.com>
---
 arch/arm64/kernel/setup.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index f3067d4d4e35..6f8d814c4e5c 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -568,3 +568,22 @@ const struct seq_operations cpuinfo_op = {
 	.stop	= c_stop,
 	.show	= c_show
 };
+
+/*
+ * Temporary hack to avoid need for console= on command line
+ */
+static int __init arm64_console_setup(void)
+{
+	/* Allow cmdline to override our assumed preferences */
+	if (console_set_on_cmdline)
+		return 0;
+
+	if (IS_ENABLED(CONFIG_SERIAL_AMBA_PL011))
+		add_preferred_console("ttyAMA", 0, "115200");
+
+	if (IS_ENABLED(CONFIG_SERIAL_8250))
+		add_preferred_console("ttyS", 0, "115200");
+
+	return 0;
+}
+early_initcall(arm64_console_setup);