freescale/imx6-sabresd: document how to create a bootable SD

Document how to create a bootable SD card for the two supported SABRESD cards:
i.MX6Q and i.MX6DL.

The SD card creation relies on an ad-hoc script.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Cc: Gilles Talis <gilles.talis@gmail.com>
Cc: Gary Bisson <bisson.gary@gmail.com>
Cc: Vincent Stehlé <vincent.stehle@freescale.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

board/freescale/imx6sabresd/create-boot-sd.sh

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+#!/bin/sh
+
+set -u
+set -e
+
+PROGNAME=$(basename $0)
+
+usage()
+{
+    echo "Create an SD card that boots on an i.MX6DL SABRESD board."
+    echo "It is supposed to work also for the i.MX6Q SABRESD board, but"
+    echo "it this is not tested."
+    echo
+    echo "Note: all data on the the card will be completely deleted!"
+    echo "Use with care!"
+    echo "Superuser permissions may be required to write to the device."
+    echo
+    echo "Usage: ${PROGNAME} <sd_block_device>"
+    echo "Arguments:"
+    echo "  <sd_block_device>     The device to be written to"
+    echo
+    echo "Example: ${PROGNAME} /dev/mmcblk0"
+    echo
+}
+
+if [ $# -ne 1 ]; then
+    usage
+    exit 1
+fi
+
+if [ $(id -u) -ne 0 ]; then
+    echo "${PROGNAME} must be run as root"
+    exit 1
+fi
+
+DEV=${1}
+
+# The partition name prefix depends on the device name:
+# - /dev/sde -> /dev/sde1
+# - /dev/mmcblk0 -> /dev/mmcblk0p1
+if echo ${DEV}|grep -q mmcblk ; then
+    PART="p"
+else
+    PART=""
+fi
+
+PART1=${DEV}${PART}1
+PART2=${DEV}${PART}2
+
+# Unmount the partitions if mounted
+umount ${PART1} || true
+umount ${PART2} || true
+
+# First, clear the card
+dd if=/dev/zero of=${DEV} bs=1M count=20
+
+sync
+
+# Partition the card.
+# SD layout for i.MX6 boot:
+# - Bootloader at offset 1024
+# - FAT partition starting at 1MB offset, containing uImage and *.dtb
+# - ext2/3 partition formatted as ext2 or ext3, containing the root filesystem.
+sfdisk ${DEV} <<EOF
+32,480,b
+512,,L
+EOF
+
+sync
+
+# Copy the bootloader at offset 1024
+dd if=output/images/u-boot.imx of=${DEV} obs=512 seek=2
+
+# Prepare a temp dir for mounting partitions
+TMPDIR=$(mktemp -d)
+
+# FAT partition: kernel and DTBs
+mkfs.vfat ${PART1}
+mount ${PART1} ${TMPDIR}
+cp output/images/uImage ${TMPDIR}/
+cp output/images/*.dtb  ${TMPDIR}/
+sync
+umount ${TMPDIR}
+
+# ext2 partition: root filesystem
+mkfs.ext2 ${PART2}
+mount ${PART2} ${TMPDIR}
+tar -C ${TMPDIR}/ -xf output/images/rootfs.tar
+sync
+umount ${TMPDIR}
+
+# Cleanup
+rmdir ${TMPDIR}
+sync
+echo Done

board/freescale/imx6sabresd/readme.txt

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+*******************************************************
+Freescale i.MX6Q and i.MX6DL SABRESD development boards
+*******************************************************
+
+This file documents the Buildroot support for the Freescale SABRE Board for
+Smart Devices Based on the i.MX 6 Series (SABRESD).
+
+Read the SABRESD Quick Start Guide for an introduction to the board:
+http://cache.freescale.com/files/32bit/doc/quick_start_guide/SABRESDB_IMX6_QSG.pdf
+
+Build
+=====
+
+First, configure Buildroot for your SABRESD board.
+For i.MX6Q:
+
+  make freescale_imx6qsabresd_defconfig
+
+For i.MX6DL:
+
+  make freescale_imx6dlsabresd_defconfig
+
+Build all components:
+
+  make
+
+You will find in ./output/images/ the following files:
+  - imx6dl-sabresd.dtb or imx6q-sabresd.dtb
+  - rootfs.ext2
+  - rootfs.tar
+  - u-boot.imx
+  - uImage
+
+Create a bootable SD card
+=========================
+
+To determine the device associated to the SD card have a look in the
+/proc/partitions file:
+
+  cat /proc/partitions
+
+Run the following script as root on your SD card. This will partition the card
+and copy the bootloader, kernel, DTBs and root filesystem as needed.
+
+*** WARNING! The script will destroy all the card content. Use with care! ***
+
+  ./board/freescale/imx6sabresd/create-boot-sd.sh <your-sd-device>
+
+Boot the SABRESD board
+======================
+
+To boot your newly created system (refer to the SABRESD Quick Start Guide for
+guidance):
+- insert the SD card in the SD3 slot of the board;
+- locate the BOOT dip switches (SW6), set dips 2 and 7 to ON, all others to OFF;
+- connect a Micro USB cable to Debug Port and connect using a terminal emulator
+  at 115200 bps, 8n1;
+- power on the board.
+
+Enjoy!
+
+References
+==========
+
+https://community.freescale.com/docs/DOC-95015
+https://community.freescale.com/docs/DOC-95017
+https://community.freescale.com/docs/DOC-99218