Index: head/sbin/camcontrol/camcontrol.c
===================================================================
--- head/sbin/camcontrol/camcontrol.c
+++ head/sbin/camcontrol/camcontrol.c
@@ -7788,6 +7788,7 @@
 		flags |= CAM_DIR_IN;
 		mmc_data = malloc(mmc_data_len);
 		memset(mmc_data, 0, mmc_data_len);
+		memset(&mmc_d, 0, sizeof(mmc_d));
 		mmc_d.len = mmc_data_len;
 		mmc_d.data = mmc_data;
 		mmc_d.flags = MMC_DATA_READ;
Index: head/sys/cam/mmc/mmc_da.c
===================================================================
--- head/sys/cam/mmc/mmc_da.c
+++ head/sys/cam/mmc/mmc_da.c
@@ -791,6 +791,11 @@
 	softc->state = SDDA_STATE_INIT;
 	softc->mmcdata =
 		(struct mmc_data *)malloc(sizeof(struct mmc_data), M_DEVBUF, M_NOWAIT|M_ZERO);
+	if (softc->mmcdata == NULL) {
+		printf("sddaregister: Unable to probe new device. "
+		    "Unable to allocate mmcdata\n");
+		return (CAM_REQ_CMP_ERR);
+	}
 	periph->softc = softc;
 	softc->periph = periph;
 
@@ -889,6 +894,7 @@
 	struct mmc_data d;
 
 	KASSERT(buf_len == 512, ("Buffer for ext csd must be 512 bytes"));
+	memset(&d, 0, sizeof(d));
 	d.data = rawextcsd;
 	d.len = buf_len;
 	d.flags = MMC_DATA_READ;
@@ -1013,6 +1019,7 @@
 	int err;
 
 	memset(res, 0, 64);
+	memset(&mmc_d, 0, sizeof(mmc_d));
 	mmc_d.len = 64;
 	mmc_d.data = res;
 	mmc_d.flags = MMC_DATA_READ;
@@ -1804,6 +1811,7 @@
 
 		mmcio->cmd.flags = MMC_RSP_R1 | MMC_CMD_ADTC;
 		mmcio->cmd.data = softc->mmcdata;
+		memset(mmcio->cmd.data, 0, sizeof(struct mmc_data));
 		mmcio->cmd.data->data = bp->bio_data;
 		mmcio->cmd.data->len = 512 * count;
 		mmcio->cmd.data->flags = (bp->bio_cmd == BIO_READ ? MMC_DATA_READ : MMC_DATA_WRITE);
Index: head/sys/dev/mmc/mmcreg.h
===================================================================
--- head/sys/dev/mmc/mmcreg.h
+++ head/sys/dev/mmc/mmcreg.h
@@ -197,7 +197,10 @@
 #define	MMC_DATA_READ	(1UL << 1)
 #define	MMC_DATA_STREAM	(1UL << 2)
 #define	MMC_DATA_MULTI	(1UL << 3)
+#define MMC_DATA_BLOCK_SIZE (1UL << 4)
 	struct mmc_request *mrq;
+	size_t block_size;      /* block size for CMD53 */
+	size_t block_count;     /* block count for CMD53 */
 };
 
 struct mmc_request {