diff --git a/src/mainboard/google/rex/variants/baseboard/rex/devicetree.cb b/src/mainboard/google/rex/variants/baseboard/rex/devicetree.cb
index f9eb12fe7c..d803670ca1 100644
--- a/src/mainboard/google/rex/variants/baseboard/rex/devicetree.cb
+++ b/src/mainboard/google/rex/variants/baseboard/rex/devicetree.cb
@@ -1,5 +1,11 @@
 chip soc/intel/meteorlake
 
+	# EC host command ranges are in 0x800-0x8ff & 0x200-0x20f
+	register "gen1_dec" = "0x00fc0801"
+	register "gen2_dec" = "0x000c0201"
+	# EC memory map range is 0x900-0x9ff
+	register "gen3_dec" = "0x00fc0901"
+
 	register "serial_io_uart_mode" = "{
 		[PchSerialIoIndexUART0] = PchSerialIoPci,
 		[PchSerialIoIndexUART1] = PchSerialIoDisabled,