[] [Enable eMMC HS400 mode]

[Description]
Add eMMC HS400 mode for improving IO performance.

[Release-log]
N/A

Change-Id: I9c4d9ed7cb0a5bb4deefdaa6f9d7d290115378f7
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/4989108
diff --git a/target/linux/mediatek/files-5.4/arch/arm64/boot/dts/mediatek/mt7986a-emmc-rfb.dts b/target/linux/mediatek/files-5.4/arch/arm64/boot/dts/mediatek/mt7986a-emmc-rfb.dts
index 7c0f601..9887a87 100644
--- a/target/linux/mediatek/files-5.4/arch/arm64/boot/dts/mediatek/mt7986a-emmc-rfb.dts
+++ b/target/linux/mediatek/files-5.4/arch/arm64/boot/dts/mediatek/mt7986a-emmc-rfb.dts
@@ -7,7 +7,7 @@
 	chosen {
 		bootargs = "console=ttyS0,115200n1 loglevel=8  \
 				earlycon=uart8250,mmio32,0x11002000 \
-				root=/dev/mmcblk0p7 rootfstype=squashfs,f2fs";
+				root=/dev/mmcblk0p7 rootwait rootfstype=squashfs,f2fs";
 	};
 };