diff --git a/doc/README.fsl-esdhc b/doc/README.fsl-esdhc
index b70f271..619c6b2 100644
--- a/doc/README.fsl-esdhc
+++ b/doc/README.fsl-esdhc
@@ -1,5 +1,6 @@
 CONFIG_SYS_FSL_ESDHC_LE means ESDHC IP is in little-endian mode.
 CONFIG_SYS_FSL_ESDHC_BE means ESDHC IP is in big-endian mode.
+CONFIG_SYS_FSL_ESDHC_FORCE_VSELECT forces to run at 1.8V.
 
 Accessing ESDHC registers can be determined by ESDHC IP's endian
 mode or processor's endian mode.