mediatek: make emmc image generation work on mt7622

Signed-off-by: John Crispin <john@phrozen.org>

target/linux/mediatek/image/Makefile

@@ -12,7 +12,7 @@ define Build/sysupgrade-emmc
 	rm -f $@.recovery
 	mkfs.fat -C $@.recovery 3070
 
-	./gen_mt7623_emmc_img.sh $@ \
+	./gen_$(SUBTARGET)_emmc_img.sh $@ \
 		$(IMAGE_KERNEL) \
 		$@.recovery \
 		$(IMAGE_ROOTFS)

target/linux/mediatek/image/gen_mt7622_emmc_img.sh

@@ -0,0 +1,19 @@
+#!/bin/sh
+
+OUTPUT_FILE=$1
+KERNEL_FILE=$2
+RECOVERY_FILE=$3
+ROOTFS_FILE=$4
+
+BS=512
+
+#RECOVERY_OFFSET= kernel size / BS = 20M / 512 (blocks)
+RECOVERY_OFFSET=40960
+
+#ROOTFS_OFFSET = RECOVERY_OFFSET + (RECOVERY_SIZE / BS)
+#	       = 40960 + (10M  / 512) (blocks)
+ROOTFS_OFFSET=61440
+dd bs="$BS" of="$OUTPUT_FILE" if="$KERNEL_FILE"
+dd bs="$BS" of="$OUTPUT_FILE" if="$RECOVERY_FILE" seek="$RECOVERY_OFFSET"
+dd bs="$BS" of="$OUTPUT_FILE" if="$ROOTFS_FILE" seek="$ROOTFS_OFFSET"
+dd if=/dev/zero of="$OUTPUT_FILE" bs=128k count=1 oflag=append conv=notrunc