[meta-freescale] [meta-fsl-arm][RFC][PATCH] image_types_fsl: Add extlinux support

[Nikolay Dimitrov]

Add support for booting via extlinux. This feature is supported only for U-Boot.
Here is how it works - during boot U-Boot scans through a list of boot drives
to find a partition containing the extlinux config file (this partition
should be either marked as a bootable, or should be the 1st one of all the
non-bootable partitions on the disk). The extlinux.conf file should be located
on one of the following paths:

/boot/extlinux/extlinux.conf
/extlinux/extlinux.conf

This patch uses the /extlinux/extlinux.conf path, in order to avoid funny paths
(/boot/boot/...) if later the vfat bootable partition needs to be mounted
(usually done at /boot).

Here's an example extlinux.conf:

default yocto
label yocto
        kernel /zImage
        devicetree /imx6dl-riotboard.dtb
        append console=ttymxc1,115200 root=/dev/mmcblk0p2 rw

And this is an example machine.conf that can use extlinux boot mechanism:

EXTLINUX_CONF = "yes"
EXTLINUX_DEVICETREE = "imx6dl-riotboard.dtb"
EXTLINUX_CONSOLE = "ttymxc1,115200"
EXTLINUX_ROOTDEV = "/dev/mmcblk0p2 rw"

Advantages:
- Boot parameters are not hardcoded in the bootloader and can be managed by
  userspace tools (including package managers)
- One board can have multiple boot configurations
- Others?

Disadvantages:
- My patch generates a simplified extlinux.conf with only 1 boot configuration.
  Would be nice if we can have board-specific extlinux.conf, but I couldn't
  find a proper way to do it
- Boot params (devicetree, console) are duplicated because the extlinux/kernel
  needs them in a format different from the existing in the machine.conf
- Others?

Signed-off-by: Nikolay Dimitrov <picmaster at mail.bg>
---
 classes/image_types_fsl.bbclass |   32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/classes/image_types_fsl.bbclass b/classes/image_types_fsl.bbclass
index 331f739..9cd9275 100644
--- a/classes/image_types_fsl.bbclass
+++ b/classes/image_types_fsl.bbclass
@@ -179,6 +179,38 @@ generate_imx_sdcard () {
 		done
 	fi
 
+	# Create extlinux config file
+	if [ "${IMAGE_BOOTLOADER}" = "u-boot" ]; then
+		if test -n "${EXTLINUX_CONF}"; then
+			if [ -z "${EXTLINUX_DEVICETREE}" ]; then
+				bberror "EXTLINUX_DEVICETREE is not defined."
+				exit 1
+			fi
+
+			if [ -z "${EXTLINUX_CONSOLE}" ]; then
+				bberror "EXTLINUX_CONSOLE is not defined."
+				exit 1
+			fi
+
+			if [ -z "${EXTLINUX_ROOTDEV}" ]; then
+				bberror "EXTLINUX_ROOTDEV is not defined."
+				exit 1
+			fi
+
+			cat > ${WORKDIR}/extlinux.conf <<EOF
+default yocto
+
+label yocto
+	kernel /${KERNEL_IMAGETYPE}
+	devicetree /${EXTLINUX_DEVICETREE}
+	append console=${EXTLINUX_CONSOLE} root=${EXTLINUX_ROOTDEV}
+EOF
+
+			mmd -i ${WORKDIR}/boot.img ::/extlinux
+			mcopy -i ${WORKDIR}/boot.img -s ${WORKDIR}/extlinux.conf ::/extlinux/
+		fi
+	fi
+
 	# Burn Partition
 	dd if=${WORKDIR}/boot.img of=${SDCARD} conv=notrunc,fsync seek=1 bs=$(expr ${IMAGE_ROOTFS_ALIGNMENT} \* 1024)
 	dd if=${SDCARD_ROOTFS} of=${SDCARD} conv=notrunc,fsync seek=1 bs=$(expr ${BOOT_SPACE_ALIGNED} \* 1024 + ${IMAGE_ROOTFS_ALIGNMENT} \* 1024)
-- 
1.7.10.4