diff --git a/drivers/net/ethernet/sfc/mcdi.c b/drivers/net/ethernet/sfc/mcdi.c
index d6d1ff19c918..3f55b16265fc 100644
--- a/drivers/net/ethernet/sfc/mcdi.c
+++ b/drivers/net/ethernet/sfc/mcdi.c
@@ -67,7 +67,7 @@ void efx_mcdi_init(struct efx_nic *efx)
 }
 
 static void efx_mcdi_copyin(struct efx_nic *efx, unsigned cmd,
-			    const u8 *inbuf, size_t inlen)
+			    const efx_dword_t *inbuf, size_t inlen)
 {
 	struct efx_mcdi_iface *mcdi = efx_mcdi(efx);
 	unsigned pdu = FR_CZ_MC_TREG_SMEM + MCDI_PDU(efx);
@@ -75,9 +75,10 @@ static void efx_mcdi_copyin(struct efx_nic *efx, unsigned cmd,
 	unsigned int i;
 	efx_dword_t hdr;
 	u32 xflags, seqno;
+	unsigned int inlen_dw = DIV_ROUND_UP(inlen, 4);
 
 	BUG_ON(atomic_read(&mcdi->state) == MCDI_STATE_QUIESCENT);
-	BUG_ON(inlen & 3 || inlen >= MC_SMEM_PDU_LEN);
+	BUG_ON(inlen > MCDI_CTL_SDU_LEN_MAX_V1);
 
 	seqno = mcdi->seqno & SEQ_MASK;
 	xflags = 0;
@@ -94,8 +95,8 @@ static void efx_mcdi_copyin(struct efx_nic *efx, unsigned cmd,
 
 	efx_writed(efx, &hdr, pdu);
 
-	for (i = 0; i < inlen; i += 4)
-		_efx_writed(efx, *((__le32 *)(inbuf + i)), pdu + 4 + i);
+	for (i = 0; i < inlen_dw; i++)
+		efx_writed(efx, &inbuf[i], pdu + 4 + 4 * i);
 
 	/* Ensure the payload is written out before the header */
 	wmb();
@@ -104,17 +105,19 @@ static void efx_mcdi_copyin(struct efx_nic *efx, unsigned cmd,
 	_efx_writed(efx, (__force __le32) 0x45789abc, doorbell);
 }
 
-static void efx_mcdi_copyout(struct efx_nic *efx, u8 *outbuf, size_t outlen)
+static void
+efx_mcdi_copyout(struct efx_nic *efx, efx_dword_t *outbuf, size_t outlen)
 {
 	struct efx_mcdi_iface *mcdi = efx_mcdi(efx);
 	unsigned int pdu = FR_CZ_MC_TREG_SMEM + MCDI_PDU(efx);
+	unsigned int outlen_dw = DIV_ROUND_UP(outlen, 4);
 	int i;
 
 	BUG_ON(atomic_read(&mcdi->state) == MCDI_STATE_QUIESCENT);
-	BUG_ON(outlen & 3 || outlen >= MC_SMEM_PDU_LEN);
+	BUG_ON(outlen > MCDI_CTL_SDU_LEN_MAX_V1);
 
-	for (i = 0; i < outlen; i += 4)
-		*((__le32 *)(outbuf + i)) = _efx_readd(efx, pdu + 4 + i);
+	for (i = 0; i < outlen_dw; i++)
+		efx_readd(efx, &outbuf[i], pdu + 4 + 4 * i);
 }
 
 static int efx_mcdi_poll(struct efx_nic *efx)
@@ -328,7 +331,8 @@ static void efx_mcdi_ev_cpl(struct efx_nic *efx, unsigned int seqno,
 }
 
 int efx_mcdi_rpc(struct efx_nic *efx, unsigned cmd,
-		 const u8 *inbuf, size_t inlen, u8 *outbuf, size_t outlen,
+		 const efx_dword_t *inbuf, size_t inlen,
+		 efx_dword_t *outbuf, size_t outlen,
 		 size_t *outlen_actual)
 {
 	efx_mcdi_rpc_start(efx, cmd, inbuf, inlen);
@@ -336,8 +340,8 @@ int efx_mcdi_rpc(struct efx_nic *efx, unsigned cmd,
 				   outbuf, outlen, outlen_actual);
 }
 
-void efx_mcdi_rpc_start(struct efx_nic *efx, unsigned cmd, const u8 *inbuf,
-			size_t inlen)
+void efx_mcdi_rpc_start(struct efx_nic *efx, unsigned cmd,
+			const efx_dword_t *inbuf, size_t inlen)
 {
 	struct efx_mcdi_iface *mcdi = efx_mcdi(efx);
 
@@ -354,7 +358,8 @@ void efx_mcdi_rpc_start(struct efx_nic *efx, unsigned cmd, const u8 *inbuf,
 }
 
 int efx_mcdi_rpc_finish(struct efx_nic *efx, unsigned cmd, size_t inlen,
-			u8 *outbuf, size_t outlen, size_t *outlen_actual)
+			efx_dword_t *outbuf, size_t outlen,
+			size_t *outlen_actual)
 {
 	struct efx_mcdi_iface *mcdi = efx_mcdi(efx);
 	int rc;
@@ -393,7 +398,7 @@ int efx_mcdi_rpc_finish(struct efx_nic *efx, unsigned cmd, size_t inlen,
 
 		if (rc == 0) {
 			efx_mcdi_copyout(efx, outbuf,
-					 min(outlen, mcdi->resplen + 3) & ~0x3);
+					 min(outlen, mcdi->resplen));
 			if (outlen_actual != NULL)
 				*outlen_actual = resplen;
 		} else if (cmd == MC_CMD_REBOOT && rc == -EIO)
diff --git a/drivers/net/ethernet/sfc/mcdi.h b/drivers/net/ethernet/sfc/mcdi.h
index f8ab64f0efb1..28657a186761 100644
--- a/drivers/net/ethernet/sfc/mcdi.h
+++ b/drivers/net/ethernet/sfc/mcdi.h
@@ -67,16 +67,18 @@ struct efx_mcdi_mon {
 
 extern void efx_mcdi_init(struct efx_nic *efx);
 
-extern int efx_mcdi_rpc(struct efx_nic *efx, unsigned cmd, const u8 *inbuf,
-			size_t inlen, u8 *outbuf, size_t outlen,
+extern int efx_mcdi_rpc(struct efx_nic *efx, unsigned cmd,
+			const efx_dword_t *inbuf, size_t inlen,
+			efx_dword_t *outbuf, size_t outlen,
 			size_t *outlen_actual);
 
 extern void efx_mcdi_rpc_start(struct efx_nic *efx, unsigned cmd,
-			       const u8 *inbuf, size_t inlen);
+			       const efx_dword_t *inbuf, size_t inlen);
 extern int efx_mcdi_rpc_finish(struct efx_nic *efx, unsigned cmd, size_t inlen,
-			       u8 *outbuf, size_t outlen,
+			       efx_dword_t *outbuf, size_t outlen,
 			       size_t *outlen_actual);
 
+
 extern int efx_mcdi_poll_reboot(struct efx_nic *efx);
 extern void efx_mcdi_mode_poll(struct efx_nic *efx);
 extern void efx_mcdi_mode_event(struct efx_nic *efx);
@@ -85,14 +87,21 @@ extern void efx_mcdi_process_event(struct efx_channel *channel,
 				   efx_qword_t *event);
 extern void efx_mcdi_sensor_event(struct efx_nic *efx, efx_qword_t *ev);
 
+/* We expect that 16- and 32-bit fields in MCDI requests and responses
+ * are appropriately aligned.  Also, on Siena we must copy to the MC
+ * shared memory strictly 32 bits at a time, so add any necessary
+ * padding.
+ */
 #define MCDI_DECLARE_BUF(_name, _len)					\
-	u8 _name[ALIGN(_len, 4)]
+	efx_dword_t _name[DIV_ROUND_UP(_len, 4)]
 #define _MCDI_PTR(_buf, _offset)					\
 	((u8 *)(_buf) + (_offset))
 #define MCDI_PTR(_buf, _field)						\
 	_MCDI_PTR(_buf, MC_CMD_ ## _field ## _OFST)
+#define _MCDI_CHECK_ALIGN(_ofst, _align)				\
+	((_ofst) + BUILD_BUG_ON_ZERO((_ofst) & (_align - 1)))
 #define _MCDI_DWORD(_buf, _field)					\
-	((efx_dword_t *)MCDI_PTR(_buf, _field))
+	((_buf) + (_MCDI_CHECK_ALIGN(MC_CMD_ ## _field ## _OFST, 4) >> 2))
 
 #define MCDI_SET_DWORD(_buf, _field, _value)				\
 	EFX_POPULATE_DWORD_1(*_MCDI_DWORD(_buf, _field), EFX_DWORD_0, _value)
@@ -109,22 +118,23 @@ extern void efx_mcdi_sensor_event(struct efx_nic *efx, efx_qword_t *ev);
 		(MC_CMD_ ## _type ## _ ## _field ## _LBN & 0x1f) +	\
 		MC_CMD_ ## _type ## _ ## _field ## _WIDTH - 1)
 
-#define _MCDI_ARRAY_PTR(_buf, _field, _index)				\
-	(MCDI_PTR(_buf, _field) +					\
-	 (_index) * MC_CMD_ ## _field ## _LEN)
+#define _MCDI_ARRAY_PTR(_buf, _field, _index, _align)			\
+	(_MCDI_PTR(_buf, _MCDI_CHECK_ALIGN(MC_CMD_ ## _field ## _OFST, _align))\
+	 + (_index) * _MCDI_CHECK_ALIGN(MC_CMD_ ## _field ## _LEN, _align))
 #define MCDI_DECLARE_STRUCT_PTR(_name)					\
-	u8 *_name
-#define MCDI_ARRAY_STRUCT_PTR _MCDI_ARRAY_PTR
+	efx_dword_t *_name
+#define MCDI_ARRAY_STRUCT_PTR(_buf, _field, _index)			\
+	((efx_dword_t *)_MCDI_ARRAY_PTR(_buf, _field, _index, 4))
 #define MCDI_VAR_ARRAY_LEN(_len, _field)				\
 	min_t(size_t, MC_CMD_ ## _field ## _MAXNUM,			\
 	      ((_len) - MC_CMD_ ## _field ## _OFST) / MC_CMD_ ## _field ## _LEN)
 #define MCDI_ARRAY_WORD(_buf, _field, _index)				\
 	(BUILD_BUG_ON_ZERO(MC_CMD_ ## _field ## _LEN != 2) +		\
 	 le16_to_cpu(*(__force const __le16 *)				\
-		     _MCDI_ARRAY_PTR(_buf, _field, _index)))
+		     _MCDI_ARRAY_PTR(_buf, _field, _index, 2)))
 #define _MCDI_ARRAY_DWORD(_buf, _field, _index)				\
 	(BUILD_BUG_ON_ZERO(MC_CMD_ ## _field ## _LEN != 4) +		\
-	 (efx_dword_t *)_MCDI_ARRAY_PTR(_buf, _field, _index))
+	 (efx_dword_t *)_MCDI_ARRAY_PTR(_buf, _field, _index, 4))
 #define MCDI_SET_ARRAY_DWORD(_buf, _field, _index, _value)		\
 	EFX_SET_DWORD_FIELD(*_MCDI_ARRAY_DWORD(_buf, _field, _index),	\
 			    EFX_DWORD_0, _value)
diff --git a/drivers/net/ethernet/sfc/ptp.c b/drivers/net/ethernet/sfc/ptp.c
index ec2cf4d7c9b7..5612021d960a 100644
--- a/drivers/net/ethernet/sfc/ptp.c
+++ b/drivers/net/ethernet/sfc/ptp.c
@@ -571,9 +571,8 @@ static int efx_ptp_xmit_skb(struct efx_nic *efx, struct sk_buff *skb)
 	struct efx_ptp_data *ptp_data = efx->ptp_data;
 	struct skb_shared_hwtstamps timestamps;
 	int rc = -EIO;
-	/* MCDI driver requires word aligned lengths */
-	size_t len = ALIGN(MC_CMD_PTP_IN_TRANSMIT_LEN(skb->len), 4);
 	MCDI_DECLARE_BUF(txtime, MC_CMD_PTP_OUT_TRANSMIT_LEN);
+	size_t len;
 
 	MCDI_SET_DWORD(ptp_data->txbuf, PTP_IN_OP, MC_CMD_PTP_OP_TRANSMIT);
 	MCDI_SET_DWORD(ptp_data->txbuf, PTP_IN_TRANSMIT_LENGTH, skb->len);
@@ -591,9 +590,10 @@ static int efx_ptp_xmit_skb(struct efx_nic *efx, struct sk_buff *skb)
 	skb_copy_from_linear_data(skb,
 				  MCDI_PTR(ptp_data->txbuf,
 					   PTP_IN_TRANSMIT_PACKET),
-				  len);
-	rc = efx_mcdi_rpc(efx, MC_CMD_PTP, ptp_data->txbuf, len, txtime,
-			  sizeof(txtime), &len);
+				  skb->len);
+	rc = efx_mcdi_rpc(efx, MC_CMD_PTP,
+			  ptp_data->txbuf, MC_CMD_PTP_IN_TRANSMIT_LEN(skb->len),
+			  txtime, sizeof(txtime), &len);
 	if (rc != 0)
 		goto fail;