Index: sys/dev/sdmmc/sdhc.c
===================================================================
RCS file: /cvsroot/src/sys/dev/sdmmc/sdhc.c,v
retrieving revision 1.103
diff -p -u -r1.103 sdhc.c
--- sys/dev/sdmmc/sdhc.c	3 Jul 2019 23:10:08 -0000	1.103
+++ sys/dev/sdmmc/sdhc.c	16 Aug 2019 06:46:12 -0000
@@ -98,6 +98,8 @@ struct sdhc_host {
 	bus_dmamap_t		adma_map;
 	bus_dma_segment_t	adma_segs[1];
 	void			*adma2;
+
+	uint8_t			vdd;	/* last vdd setting */
 };
 
 #define HDEVNAME(hp)	(device_xname((hp)->sc->sc_dev))
@@ -929,6 +931,12 @@ sdhc_bus_power(sdmmc_chipset_handle_t sc
 		goto out;
 	}
 
+	/*
+	 * if voltage doesn't change, do nothing
+	 */
+	if (vdd == hp->vdd)
+		goto out;
+
 	if (!ISSET(hp->sc->sc_flags, SDHC_FLAG_ENHANCED)) {
 		/*
 		 * Enable bus power.  Wait at least 1 ms (or 74 clocks) plus
@@ -960,6 +968,9 @@ sdhc_bus_power(sdmmc_chipset_handle_t sc
 		}
 	}
 
+	/* power successfully changed */
+	hp->vdd = vdd;
+
 out:
 	mutex_exit(&hp->intr_lock);