configs: add lego_ev3_defconfig

Add initial support for the Lego Mindstorms EV3 programmable brick.

The Lego Mindstorms EV3 brick comprises a Texas Instruments AM1808 SoC, with
an ARM 926EJ-S main processor running at 300 MHz.
https://en.wikipedia.org/wiki/Lego_Mindstorms_EV3

This configuration uses the Linux kernel of the ev3dev project.
https://github.com/mindboards/ev3sources

More info is available in the board/lego/ev3/readme.txt file, shamelessly
documented in the same way as the SoCkit folks did.

[Peter: lock kernel headers to match]
Signed-off-by: Vincent Stehlé <vincent.stehle@laposte.net>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

board/lego/ev3/readme.txt

@@ -0,0 +1,135 @@
+Lego Mindstorms EV3
+
+Intro
+=====
+
+This is the buildroot basic board support for the Lego Mindstorms EV3
+programmable brick. No support for sensors and drivers is provided for the
+moment.
+
+The Lego Mindstorms EV3 brick comprises a Texas Instruments AM1808 SoC, with
+an ARM 926EJ-S main processor running at 300 MHz.
+See:
+- https://en.wikipedia.org/wiki/Lego_Mindstorms_EV3
+- http://www.lego.com/en-us/mindstorms/products/ev3/31313-mindstorms-ev3/
+- http://www.ti.com/product/am1808
+
+The buildroot configuration uses the Linux kernel of the ev3dev project.
+See:
+- http://botbench.com/blog/2013/07/31/lego-mindstorms-ev3-source-code-available/
+- https://github.com/mindboards/ev3sources
+
+Note that the EV3 configuration uses gcc 4.7, as the boot is broken with gcc
+4.8.
+
+How it works
+============
+
+Boot process :
+--------------
+
+The u-boot on-board the EV3 brick has provision to boot a Linux kernel from the
+external µSD card. It will try to load a uImage from the first µSD card
+partition, which must be formatted with a FAT filesystem.
+
+How to build it
+===============
+
+Configure Buildroot
+-------------------
+
+The lego_ev3_defconfig configuration provides basic support to boot on the Lego
+Mindstorms EV3 programmable brick:
+
+  $ make lego_ev3_defconfig
+
+Build everything
+----------------
+
+Note: you will need to have access to the network, since Buildroot will
+download the packages' sources.
+
+  $ make
+
+Result of the build
+-------------------
+
+After building, you should obtain this tree:
+
+    output/images/
+    ├── rootfs.ext2
+    ├── rootfs.ext3 -> rootfs.ext2
+    └── uImage
+
+
+Prepare your SDcard
+===================
+
+The following µSD card layout is recommended:
+
+- First partition formated with a FAT filesystem, containing the uImage.
+- Second partition formatted as ext2 or ext3, containing the root filesystem.
+
+Create the SDcard partition table
+----------------------------------
+
+Determine the device associated to the SD card :
+
+  $ cat /proc/partitions
+
+Let's assume it is /dev/mmcblk0 :
+
+  $ sudo fdisk /dev/mmcblk0
+
+Delete all previous partitions by creating a new disklabel with 'o', then
+create the new partition table, using these options, pressing enter after each
+one:
+
+  * n p 1 2048 +10M t c
+  * n p 2 22528 +256M
+
+Using the 'p' option, the SD card's partition must look like this :
+
+Device          Boot  Start     End  Blocks  Id System
+/dev/mmcblk0p1         2048   22527   10240   c  W95 FAT32 (LBA)
+/dev/mmcblk0p2        22528  546815  262144  83  Linux
+
+Then write the partition table using 'w' and exit.
+
+Make partition one a DOS partition :
+
+  $ sudo mkfs.vfat /dev/mmcblk0p1
+
+Install the binaries to the SDcard
+----------------------------------
+
+Remember your binaries are located in output/images/, go inside that directory :
+
+  $ cd output/images
+
+Copy the Linux kernel:
+
+  $ sudo mkdir /mnt/sdcard
+  $ sudo mount /dev/mmcblk0p1 /mnt/sdcard
+  $ sudo cp uImage /mnt/sdcard
+  $ sudo umount /mnt/sdcard
+
+Copy the rootfs :
+
+  $ sudo dd if=rootfs.ext3 of=/dev/mmcblk0p2 bs=1M
+  $ sync
+
+It's Done!
+
+Finish
+======
+
+Eject your µSD card, insert it in your Lego EV3, and power it up.
+
+To have a serial console, you will need a proper USB to Lego serial port
+adapter plugged into the EV3 sensors port 1.
+See:
+- http://botbench.com/blog/2013/08/15/ev3-creating-console-cable/
+- http://botbench.com/blog/2013/08/05/mindsensors-ev3-usb-console-adapter/
+
+The serial port config to use is 115200/8-N-1.

configs/lego_ev3_defconfig

@@ -0,0 +1,28 @@
+# architecture
+BR2_arm=y
+BR2_arm926t=y
+
+# toolchain
+# Use gcc 4.7, as gcc 4.8 breaks the boot.
+BR2_GCC_VERSION_4_7_X=y
+
+# system
+BR2_TARGET_GENERIC_GETTY=y
+BR2_TARGET_GENERIC_GETTY_PORT="ttyS1"
+
+# Lock to 3.3 headers to avoid breaking with newer kernels
+BR2_KERNEL_HEADERS_VERSION=y
+BR2_DEFAULT_KERNEL_VERSION="3.3"
+BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_3_3=y
+
+# Kernel
+BR2_LINUX_KERNEL=y
+BR2_LINUX_KERNEL_CUSTOM_GIT=y
+BR2_LINUX_KERNEL_CUSTOM_REPO_URL="https://github.com/mindboards/ev3dev-kernel.git"
+BR2_LINUX_KERNEL_CUSTOM_REPO_VERSION="v3.3.0-2-ev3dev_0"
+BR2_LINUX_KERNEL_DEFCONFIG="ev3dev"
+
+# filesystem
+BR2_TARGET_ROOTFS_EXT2=y
+BR2_TARGET_ROOTFS_EXT2_3=y
+# BR2_TARGET_ROOTFS_TAR is not set