base-files: upgrade: nand: add JFFS2 cleanmarkers support

Some Broadcom MIPS devices require JFFS2 cleanmarkers to be present on the
kernel partition or the bootloader will identify the partition as corrupt and
won't boot the kernel.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

package/base-files/files/lib/upgrade/nand.sh

@@ -301,6 +301,7 @@ nand_upgrade_fit() {
 nand_upgrade_tar() {
 	local tar_file="$1"
 	local gz="$2"
+	local jffs2_markers="${CI_JFFS2_CLEAN_MARKERS:-0}"
 
 	# WARNING: This fails if tar contains more than one 'sysupgrade-*' directory.
 	local board_dir="$(tar t${gz}f "$tar_file" | grep -m 1 '^sysupgrade-.*/$')"
@@ -329,6 +330,7 @@ nand_upgrade_tar() {
 			ubi_kernel_length="$kernel_length"
 		fi
 	fi
+
 	local has_env=0
 	nand_upgrade_prepare_ubi "$rootfs_length" "$rootfs_type" "$ubi_kernel_length" "$has_env" || return 1
 
@@ -340,8 +342,14 @@ nand_upgrade_tar() {
 	fi
 	if [ "$kernel_length" ]; then
 		if [ "$kernel_mtd" ]; then
+			if [ "$jffs2_markers" = 1 ]; then
+				flash_erase -j "/dev/mtd${kernel_mtd}" 0 0
+				tar xO${gz}f "$tar_file" "$board_dir/kernel" | \
+					nandwrite "/dev/mtd${kernel_mtd}" -
+			else
 				tar xO${gz}f "$tar_file" "$board_dir/kernel" | \
 					mtd write - "$CI_KERNPART"
+			fi
 		else
 			local ubidev="$( nand_find_ubi "${CI_KERN_UBIPART:-$CI_UBIPART}" )"
 			local kern_ubivol="$( nand_find_volume $ubidev "$CI_KERNPART" )"