linux-kernel - [PATCH 1/2] ARM: dts: da850-lego-ev3: Add node for reboot modes

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Message-Id: <1515723685-19286-2-git-send-email-david@lechnology.com>
Date:   Thu, 11 Jan 2018 20:21:24 -0600
From:   David Lechner <david@...hnology.com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     David Lechner <david@...hnology.com>, Sekhar Nori <nsekhar@...com>,
        Kevin Hilman <khilman@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] ARM: dts: da850-lego-ev3: Add node for reboot modes

This adds a new node for reboot modes on LEGO MINDSTORMS EV3. The EV3's
bootloader looks for a magic number in the ARM local RAM and if found,
it will boot into a special firmware update mode where the flash memory
can be written via USB.

This has been testing working using the command:

    # systemctl reboot loader

Signed-off-by: David Lechner <david@...hnology.com>
---
 arch/arm/boot/dts/da850-lego-ev3.dts | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/arch/arm/boot/dts/da850-lego-ev3.dts b/arch/arm/boot/dts/da850-lego-ev3.dts
index e4bbf48..1cb2ff1 100644
--- a/arch/arm/boot/dts/da850-lego-ev3.dts
+++ b/arch/arm/boot/dts/da850-lego-ev3.dts
@@ -212,6 +212,23 @@
 		compatible = "gpio-backlight";
 		gpios = <&gpio 44 GPIO_ACTIVE_HIGH>;
 	};
+
+	/* ARM local RAM */
+	memory@...f0000 {
+		compatible = "syscon", "simple-mfd";
+		reg = <0xffff0000 0x2000>; /* 8k */
+
+		/*
+		 * The I2C bootloader looks for this magic value to either
+		 * boot normally or boot into a firmware update mode.
+		 */
+		reboot-mode {
+			compatible = "syscon-reboot-mode";
+			offset = <0x1ffc>;
+			mode-normal = <0x00000000>;
+			mode-loader = <0x5555aaaa>;
+		};
+	};
 };
 
 &cpu {
-- 
2.7.4