diff --git a/drivers/mmc/host/tmio_mmc.h b/drivers/mmc/host/tmio_mmc.h
index b161dfadfec25dc7c7c2f9f85c944209ca4fe105..e3e96178acaab4562cb0858c5c8aa2e47ef36abd 100644
--- a/drivers/mmc/host/tmio_mmc.h
+++ b/drivers/mmc/host/tmio_mmc.h
@@ -81,9 +81,11 @@
 #define TMIO_STAT_CMD_BUSY      BIT(30)
 #define TMIO_STAT_ILL_ACCESS    BIT(31)
 
+/* Definitions for values the CTL_SD_CARD_CLK_CTL register can take */
 #define	CLK_CTL_DIV_MASK	0xff
 #define	CLK_CTL_SCLKEN		BIT(8)
 
+/* Definitions for values the CTL_SD_MEM_CARD_OPT register can take */
 #define CARD_OPT_WIDTH8		BIT(13)
 #define CARD_OPT_WIDTH		BIT(15)