Index: head/sys/dev/sfxge/common/ef10_ev.c
===================================================================
--- head/sys/dev/sfxge/common/ef10_ev.c
+++ head/sys/dev/sfxge/common/ef10_ev.c
@@ -100,11 +100,10 @@
 	__in		uint32_t timer_ns)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_SET_EVQ_TMR_IN_LEN,
-			    MC_CMD_SET_EVQ_TMR_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_SET_EVQ_TMR_IN_LEN,
+		MC_CMD_SET_EVQ_TMR_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_SET_EVQ_TMR;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_SET_EVQ_TMR_IN_LEN;
@@ -150,9 +149,9 @@
 	__in		boolean_t low_latency)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[
-	    MAX(MC_CMD_INIT_EVQ_IN_LEN(EFX_EVQ_NBUFS(EFX_EVQ_MAXNEVS)),
-		MC_CMD_INIT_EVQ_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload,
+		MC_CMD_INIT_EVQ_IN_LEN(EFX_EVQ_NBUFS(EFX_EVQ_MAXNEVS)),
+		MC_CMD_INIT_EVQ_OUT_LEN);
 	efx_qword_t *dma_addr;
 	uint64_t addr;
 	int npages;
@@ -167,7 +166,6 @@
 		goto fail1;
 	}
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_INIT_EVQ;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_INIT_EVQ_IN_LEN(npages);
@@ -287,9 +285,9 @@
 	__in		uint32_t flags)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[
-		MAX(MC_CMD_INIT_EVQ_V2_IN_LEN(EFX_EVQ_NBUFS(EFX_EVQ_MAXNEVS)),
-		    MC_CMD_INIT_EVQ_V2_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload,
+		MC_CMD_INIT_EVQ_V2_IN_LEN(EFX_EVQ_NBUFS(EFX_EVQ_MAXNEVS)),
+		MC_CMD_INIT_EVQ_V2_OUT_LEN);
 	boolean_t interrupting;
 	unsigned int evq_type;
 	efx_qword_t *dma_addr;
@@ -304,7 +302,6 @@
 		goto fail1;
 	}
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_INIT_EVQ;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_INIT_EVQ_V2_IN_LEN(npages);
@@ -411,11 +408,10 @@
 	__in		uint32_t instance)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_FINI_EVQ_IN_LEN,
-			    MC_CMD_FINI_EVQ_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_FINI_EVQ_IN_LEN,
+		MC_CMD_FINI_EVQ_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_FINI_EVQ;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_FINI_EVQ_IN_LEN;
@@ -630,8 +626,8 @@
 	__in		efx_qword_t data)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_DRIVER_EVENT_IN_LEN,
-			    MC_CMD_DRIVER_EVENT_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_DRIVER_EVENT_IN_LEN,
+		MC_CMD_DRIVER_EVENT_OUT_LEN);
 	efx_rc_t rc;
 
 	req.emr_cmd = MC_CMD_DRIVER_EVENT;
Index: head/sys/dev/sfxge/common/ef10_filter.c
===================================================================
--- head/sys/dev/sfxge/common/ef10_filter.c
+++ head/sys/dev/sfxge/common/ef10_filter.c
@@ -199,12 +199,11 @@
 	__inout		ef10_filter_handle_t *handle)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_FILTER_OP_V3_IN_LEN,
-			    MC_CMD_FILTER_OP_EXT_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_FILTER_OP_V3_IN_LEN,
+		MC_CMD_FILTER_OP_EXT_OUT_LEN);
 	efx_filter_match_flags_t match_flags;
 	efx_rc_t rc;
 
-	memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_FILTER_OP;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_FILTER_OP_V3_IN_LEN;
@@ -403,11 +402,10 @@
 	__inout		ef10_filter_handle_t *handle)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_FILTER_OP_EXT_IN_LEN,
-			    MC_CMD_FILTER_OP_EXT_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_FILTER_OP_EXT_IN_LEN,
+		MC_CMD_FILTER_OP_EXT_OUT_LEN);
 	efx_rc_t rc;
 
-	memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_FILTER_OP;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_FILTER_OP_EXT_IN_LEN;
@@ -977,13 +975,12 @@
 	__out				size_t *list_lengthp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_PARSER_DISP_INFO_IN_LEN,
-			    MC_CMD_GET_PARSER_DISP_INFO_OUT_LENMAX)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_PARSER_DISP_INFO_IN_LEN,
+		MC_CMD_GET_PARSER_DISP_INFO_OUT_LENMAX);
 	size_t matches_count;
 	size_t list_size;
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_PARSER_DISP_INFO;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_PARSER_DISP_INFO_IN_LEN;
Index: head/sys/dev/sfxge/common/ef10_intr.c
===================================================================
--- head/sys/dev/sfxge/common/ef10_intr.c
+++ head/sys/dev/sfxge/common/ef10_intr.c
@@ -78,8 +78,8 @@
 	__in		unsigned int level)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_TRIGGER_INTERRUPT_IN_LEN,
-			    MC_CMD_TRIGGER_INTERRUPT_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_TRIGGER_INTERRUPT_IN_LEN,
+		MC_CMD_TRIGGER_INTERRUPT_OUT_LEN);
 	efx_rc_t rc;
 
 	EFSYS_ASSERT(enp->en_family == EFX_FAMILY_HUNTINGTON ||
@@ -91,7 +91,6 @@
 		goto fail1;
 	}
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_TRIGGER_INTERRUPT;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_TRIGGER_INTERRUPT_IN_LEN;
Index: head/sys/dev/sfxge/common/ef10_mac.c
===================================================================
--- head/sys/dev/sfxge/common/ef10_mac.c
+++ head/sys/dev/sfxge/common/ef10_mac.c
@@ -102,11 +102,10 @@
 {
 	efx_port_t *epp = &(enp->en_port);
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_VADAPTOR_SET_MAC_IN_LEN,
-			    MC_CMD_VADAPTOR_SET_MAC_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_VADAPTOR_SET_MAC_IN_LEN,
+		MC_CMD_VADAPTOR_SET_MAC_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_VADAPTOR_SET_MAC;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_VADAPTOR_SET_MAC_IN_LEN;
@@ -168,11 +167,10 @@
 	__in		uint32_t mtu)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_SET_MAC_EXT_IN_LEN,
-			    MC_CMD_SET_MAC_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_SET_MAC_EXT_IN_LEN,
+		MC_CMD_SET_MAC_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_SET_MAC;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_SET_MAC_EXT_IN_LEN;
@@ -205,11 +203,10 @@
 	__out		size_t *mtu)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_SET_MAC_EXT_IN_LEN,
-			    MC_CMD_SET_MAC_V2_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_SET_MAC_EXT_IN_LEN,
+		MC_CMD_SET_MAC_V2_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_SET_MAC;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_SET_MAC_EXT_IN_LEN;
@@ -301,11 +298,10 @@
 {
 	efx_port_t *epp = &(enp->en_port);
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_SET_MAC_IN_LEN,
-			    MC_CMD_SET_MAC_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_SET_MAC_IN_LEN,
+		MC_CMD_SET_MAC_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_SET_MAC;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_SET_MAC_IN_LEN;
Index: head/sys/dev/sfxge/common/ef10_nic.c
===================================================================
--- head/sys/dev/sfxge/common/ef10_nic.c
+++ head/sys/dev/sfxge/common/ef10_nic.c
@@ -47,15 +47,14 @@
 	__out		uint32_t *portp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_PORT_ASSIGNMENT_IN_LEN,
-			    MC_CMD_GET_PORT_ASSIGNMENT_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_PORT_ASSIGNMENT_IN_LEN,
+		MC_CMD_GET_PORT_ASSIGNMENT_OUT_LEN);
 	efx_rc_t rc;
 
 	EFSYS_ASSERT(enp->en_family == EFX_FAMILY_HUNTINGTON ||
 	    enp->en_family == EFX_FAMILY_MEDFORD ||
 	    enp->en_family == EFX_FAMILY_MEDFORD2);
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_PORT_ASSIGNMENT;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_PORT_ASSIGNMENT_IN_LEN;
@@ -94,15 +93,14 @@
 	__out_opt	uint32_t *default_modep)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_PORT_MODES_IN_LEN,
-			    MC_CMD_GET_PORT_MODES_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_PORT_MODES_IN_LEN,
+		MC_CMD_GET_PORT_MODES_OUT_LEN);
 	efx_rc_t rc;
 
 	EFSYS_ASSERT(enp->en_family == EFX_FAMILY_HUNTINGTON ||
 	    enp->en_family == EFX_FAMILY_MEDFORD ||
 	    enp->en_family == EFX_FAMILY_MEDFORD2);
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_PORT_MODES;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_PORT_MODES_IN_LEN;
@@ -207,13 +205,12 @@
 	__in			uint32_t port_id)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_VADAPTOR_ALLOC_IN_LEN,
-			    MC_CMD_VADAPTOR_ALLOC_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_VADAPTOR_ALLOC_IN_LEN,
+		MC_CMD_VADAPTOR_ALLOC_OUT_LEN);
 	efx_rc_t rc;
 
 	EFSYS_ASSERT3U(enp->en_vport_id, ==, EVB_PORT_ID_NULL);
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_VADAPTOR_ALLOC;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_VADAPTOR_ALLOC_IN_LEN;
@@ -246,11 +243,10 @@
 	__in			uint32_t port_id)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_VADAPTOR_FREE_IN_LEN,
-			    MC_CMD_VADAPTOR_FREE_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_VADAPTOR_FREE_IN_LEN,
+		MC_CMD_VADAPTOR_FREE_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_VADAPTOR_FREE;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_VADAPTOR_FREE_IN_LEN;
@@ -280,15 +276,14 @@
 	__out_ecount_opt(6)	uint8_t mac_addrp[6])
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_MAC_ADDRESSES_IN_LEN,
-			    MC_CMD_GET_MAC_ADDRESSES_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_MAC_ADDRESSES_IN_LEN,
+		MC_CMD_GET_MAC_ADDRESSES_OUT_LEN);
 	efx_rc_t rc;
 
 	EFSYS_ASSERT(enp->en_family == EFX_FAMILY_HUNTINGTON ||
 	    enp->en_family == EFX_FAMILY_MEDFORD ||
 	    enp->en_family == EFX_FAMILY_MEDFORD2);
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_MAC_ADDRESSES;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_MAC_ADDRESSES_IN_LEN;
@@ -339,15 +334,14 @@
 	__out_ecount_opt(6)	uint8_t mac_addrp[6])
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_VPORT_GET_MAC_ADDRESSES_IN_LEN,
-			    MC_CMD_VPORT_GET_MAC_ADDRESSES_OUT_LENMAX)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_VPORT_GET_MAC_ADDRESSES_IN_LEN,
+		MC_CMD_VPORT_GET_MAC_ADDRESSES_OUT_LENMAX);
 	efx_rc_t rc;
 
 	EFSYS_ASSERT(enp->en_family == EFX_FAMILY_HUNTINGTON ||
 	    enp->en_family == EFX_FAMILY_MEDFORD ||
 	    enp->en_family == EFX_FAMILY_MEDFORD2);
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_VPORT_GET_MAC_ADDRESSES;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_VPORT_GET_MAC_ADDRESSES_IN_LEN;
@@ -404,15 +398,14 @@
 	__out		uint32_t *dpcpu_freqp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_CLOCK_IN_LEN,
-			    MC_CMD_GET_CLOCK_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_CLOCK_IN_LEN,
+		MC_CMD_GET_CLOCK_OUT_LEN);
 	efx_rc_t rc;
 
 	EFSYS_ASSERT(enp->en_family == EFX_FAMILY_HUNTINGTON ||
 	    enp->en_family == EFX_FAMILY_MEDFORD ||
 	    enp->en_family == EFX_FAMILY_MEDFORD2);
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_CLOCK;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_CLOCK_IN_LEN;
@@ -462,12 +455,11 @@
 	__out		uint32_t *end_paddingp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_RXDP_CONFIG_IN_LEN,
-			    MC_CMD_GET_RXDP_CONFIG_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_RXDP_CONFIG_IN_LEN,
+		MC_CMD_GET_RXDP_CONFIG_OUT_LEN);
 	uint32_t end_padding;
 	efx_rc_t rc;
 
-	memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_RXDP_CONFIG;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_RXDP_CONFIG_IN_LEN;
@@ -522,11 +514,10 @@
 	__out_opt	uint32_t *vf_nvecp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_VECTOR_CFG_IN_LEN,
-			    MC_CMD_GET_VECTOR_CFG_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_VECTOR_CFG_IN_LEN,
+		MC_CMD_GET_VECTOR_CFG_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_VECTOR_CFG;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_VECTOR_CFG_IN_LEN;
@@ -572,8 +563,8 @@
 	__out		uint32_t *vi_shiftp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_ALLOC_VIS_IN_LEN,
-			    MC_CMD_ALLOC_VIS_EXT_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_ALLOC_VIS_IN_LEN,
+		MC_CMD_ALLOC_VIS_EXT_OUT_LEN);
 	efx_rc_t rc;
 
 	if (vi_countp == NULL) {
@@ -581,7 +572,6 @@
 		goto fail1;
 	}
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_ALLOC_VIS;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_ALLOC_VIS_IN_LEN;
@@ -664,8 +654,8 @@
 	__out		efx_piobuf_handle_t *handlep)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_ALLOC_PIOBUF_IN_LEN,
-			    MC_CMD_ALLOC_PIOBUF_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_ALLOC_PIOBUF_IN_LEN,
+		MC_CMD_ALLOC_PIOBUF_OUT_LEN);
 	efx_rc_t rc;
 
 	if (handlep == NULL) {
@@ -673,7 +663,6 @@
 		goto fail1;
 	}
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_ALLOC_PIOBUF;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_ALLOC_PIOBUF_IN_LEN;
@@ -712,11 +701,10 @@
 	__in		efx_piobuf_handle_t handle)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_FREE_PIOBUF_IN_LEN,
-			    MC_CMD_FREE_PIOBUF_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_FREE_PIOBUF_IN_LEN,
+		MC_CMD_FREE_PIOBUF_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_FREE_PIOBUF;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_FREE_PIOBUF_IN_LEN;
@@ -747,11 +735,10 @@
 	__in		efx_piobuf_handle_t handle)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_LINK_PIOBUF_IN_LEN,
-			    MC_CMD_LINK_PIOBUF_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_LINK_PIOBUF_IN_LEN,
+		MC_CMD_LINK_PIOBUF_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_LINK_PIOBUF;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_LINK_PIOBUF_IN_LEN;
@@ -782,11 +769,10 @@
 	__in		uint32_t vi_index)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_UNLINK_PIOBUF_IN_LEN,
-			    MC_CMD_UNLINK_PIOBUF_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_UNLINK_PIOBUF_IN_LEN,
+		MC_CMD_UNLINK_PIOBUF_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_UNLINK_PIOBUF;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_UNLINK_PIOBUF_IN_LEN;
@@ -984,11 +970,10 @@
 	__out		uint32_t *pf_countp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_PF_COUNT_IN_LEN,
-			    MC_CMD_GET_PF_COUNT_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_PF_COUNT_IN_LEN,
+		MC_CMD_GET_PF_COUNT_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_PF_COUNT;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_PF_COUNT_IN_LEN;
@@ -1028,15 +1013,14 @@
 {
 	efx_nic_cfg_t *encp = &(enp->en_nic_cfg);
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_CAPABILITIES_IN_LEN,
-			    MC_CMD_GET_CAPABILITIES_V5_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_CAPABILITIES_IN_LEN,
+		MC_CMD_GET_CAPABILITIES_V5_OUT_LEN);
 	efx_rc_t rc;
 
 	if ((rc = ef10_mcdi_get_pf_count(enp, &encp->enc_hw_pf_count)) != 0)
 		goto fail1;
 
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_CAPABILITIES;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_CAPABILITIES_IN_LEN;
@@ -2073,8 +2057,8 @@
 	__in		efx_nic_t *enp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_ENTITY_RESET_IN_LEN,
-			    MC_CMD_ENTITY_RESET_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_ENTITY_RESET_IN_LEN,
+		MC_CMD_ENTITY_RESET_OUT_LEN);
 	efx_rc_t rc;
 
 	/* ef10_nic_reset() is called to recover from BADASSERT failures. */
@@ -2083,7 +2067,6 @@
 	if ((rc = efx_mcdi_exit_assertion_handler(enp)) != 0)
 		goto fail2;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_ENTITY_RESET;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_ENTITY_RESET_IN_LEN;
@@ -2420,11 +2403,10 @@
 	__out		uint32_t *valuep)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_NIC_GLOBAL_IN_LEN,
-			    MC_CMD_GET_NIC_GLOBAL_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_NIC_GLOBAL_IN_LEN,
+		MC_CMD_GET_NIC_GLOBAL_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_NIC_GLOBAL;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_NIC_GLOBAL_IN_LEN;
@@ -2464,10 +2446,9 @@
 	__in		uint32_t value)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MC_CMD_SET_NIC_GLOBAL_IN_LEN];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_SET_NIC_GLOBAL_IN_LEN, 0);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_SET_NIC_GLOBAL;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_SET_NIC_GLOBAL_IN_LEN;
Index: head/sys/dev/sfxge/common/ef10_phy.c
===================================================================
--- head/sys/dev/sfxge/common/ef10_phy.c
+++ head/sys/dev/sfxge/common/ef10_phy.c
@@ -269,11 +269,10 @@
 	__out		ef10_link_state_t *elsp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_LINK_IN_LEN,
-			    MC_CMD_GET_LINK_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_LINK_IN_LEN,
+		MC_CMD_GET_LINK_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_LINK;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_LINK_IN_LEN;
@@ -328,8 +327,8 @@
 {
 	efx_port_t *epp = &(enp->en_port);
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_SET_LINK_IN_LEN,
-			    MC_CMD_SET_LINK_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_SET_LINK_IN_LEN,
+		MC_CMD_SET_LINK_OUT_LEN);
 	uint32_t cap_mask;
 #if EFSYS_OPT_PHY_LED_CONTROL
 	unsigned int led_mode;
@@ -343,7 +342,6 @@
 	if (supported == B_FALSE)
 		goto out;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_SET_LINK;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_SET_LINK_IN_LEN;
@@ -491,12 +489,11 @@
 	__in		efx_nic_t *enp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_PHY_STATE_IN_LEN,
-			    MC_CMD_GET_PHY_STATE_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_PHY_STATE_IN_LEN,
+		MC_CMD_GET_PHY_STATE_OUT_LEN);
 	uint32_t state;
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_PHY_STATE;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_PHY_STATE_IN_LEN;
@@ -614,7 +611,8 @@
 	 * MCDI_CTL_SDU_LEN_MAX_V1 is large enough cover all BIST results,
 	 * whilst not wasting stack.
 	 */
-	uint8_t payload[MAX(MC_CMD_POLL_BIST_IN_LEN, MCDI_CTL_SDU_LEN_MAX_V1)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_POLL_BIST_IN_LEN,
+		MCDI_CTL_SDU_LEN_MAX_V1);
 	efx_nic_cfg_t *encp = &(enp->en_nic_cfg);
 	efx_mcdi_req_t req;
 	uint32_t value_mask = 0;
@@ -632,7 +630,6 @@
 
 	_NOTE(ARGUNUSED(type))
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_POLL_BIST;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_POLL_BIST_IN_LEN;
Index: head/sys/dev/sfxge/common/ef10_rx.c
===================================================================
--- head/sys/dev/sfxge/common/ef10_rx.c
+++ head/sys/dev/sfxge/common/ef10_rx.c
@@ -56,8 +56,8 @@
 {
 	efx_nic_cfg_t *encp = &(enp->en_nic_cfg);
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_INIT_RXQ_V3_IN_LEN,
-			    MC_CMD_INIT_RXQ_V3_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_INIT_RXQ_V3_IN_LEN,
+		MC_CMD_INIT_RXQ_V3_OUT_LEN);
 	int npages = EFX_RXQ_NBUFS(ndescs);
 	int i;
 	efx_qword_t *dma_addr;
@@ -100,7 +100,6 @@
 		want_outer_classes = B_FALSE;
 	}
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_INIT_RXQ;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_INIT_RXQ_V3_IN_LEN;
@@ -173,11 +172,10 @@
 	__in		uint32_t instance)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_FINI_RXQ_IN_LEN,
-			    MC_CMD_FINI_RXQ_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_FINI_RXQ_IN_LEN,
+		MC_CMD_FINI_RXQ_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_FINI_RXQ;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_FINI_RXQ_IN_LEN;
@@ -215,8 +213,8 @@
 	__out		uint32_t *rss_contextp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_RSS_CONTEXT_ALLOC_IN_LEN,
-			    MC_CMD_RSS_CONTEXT_ALLOC_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_RSS_CONTEXT_ALLOC_IN_LEN,
+		MC_CMD_RSS_CONTEXT_ALLOC_OUT_LEN);
 	uint32_t rss_context;
 	uint32_t context_type;
 	efx_rc_t rc;
@@ -238,7 +236,6 @@
 		goto fail2;
 	}
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_RSS_CONTEXT_ALLOC;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_RSS_CONTEXT_ALLOC_IN_LEN;
@@ -301,8 +298,8 @@
 	__in		uint32_t rss_context)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_RSS_CONTEXT_FREE_IN_LEN,
-			    MC_CMD_RSS_CONTEXT_FREE_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_RSS_CONTEXT_FREE_IN_LEN,
+		MC_CMD_RSS_CONTEXT_FREE_OUT_LEN);
 	efx_rc_t rc;
 
 	if (rss_context == EF10_RSS_CONTEXT_INVALID) {
@@ -310,7 +307,6 @@
 		goto fail1;
 	}
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_RSS_CONTEXT_FREE;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_RSS_CONTEXT_FREE_IN_LEN;
@@ -351,8 +347,8 @@
 	efx_rx_hash_type_t type_ipv6_tcp;
 	efx_rx_hash_type_t modes;
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_RSS_CONTEXT_SET_FLAGS_IN_LEN,
-			    MC_CMD_RSS_CONTEXT_SET_FLAGS_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_RSS_CONTEXT_SET_FLAGS_IN_LEN,
+		MC_CMD_RSS_CONTEXT_SET_FLAGS_OUT_LEN);
 	efx_rc_t rc;
 
 	EFX_STATIC_ASSERT(EFX_RX_CLASS_IPV4_TCP_LBN ==
@@ -377,7 +373,6 @@
 		goto fail1;
 	}
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_RSS_CONTEXT_SET_FLAGS;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_RSS_CONTEXT_SET_FLAGS_IN_LEN;
@@ -466,8 +461,8 @@
 	__in		size_t n)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_RSS_CONTEXT_SET_KEY_IN_LEN,
-			    MC_CMD_RSS_CONTEXT_SET_KEY_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_RSS_CONTEXT_SET_KEY_IN_LEN,
+		MC_CMD_RSS_CONTEXT_SET_KEY_OUT_LEN);
 	efx_rc_t rc;
 
 	if (rss_context == EF10_RSS_CONTEXT_INVALID) {
@@ -475,7 +470,6 @@
 		goto fail1;
 	}
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_RSS_CONTEXT_SET_KEY;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_RSS_CONTEXT_SET_KEY_IN_LEN;
@@ -523,8 +517,8 @@
 	__in		size_t n)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_RSS_CONTEXT_SET_TABLE_IN_LEN,
-			    MC_CMD_RSS_CONTEXT_SET_TABLE_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_RSS_CONTEXT_SET_TABLE_IN_LEN,
+		MC_CMD_RSS_CONTEXT_SET_TABLE_OUT_LEN);
 	uint8_t *req_table;
 	int i, rc;
 
@@ -533,7 +527,6 @@
 		goto fail1;
 	}
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_RSS_CONTEXT_SET_TABLE;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_RSS_CONTEXT_SET_TABLE_IN_LEN;
Index: head/sys/dev/sfxge/common/ef10_tx.c
===================================================================
--- head/sys/dev/sfxge/common/ef10_tx.c
+++ head/sys/dev/sfxge/common/ef10_tx.c
@@ -58,8 +58,8 @@
 	__in		efsys_mem_t *esmp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_INIT_TXQ_IN_LEN(EFX_TXQ_MAX_BUFS),
-			    MC_CMD_INIT_TXQ_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_INIT_TXQ_IN_LEN(EFX_TXQ_MAX_BUFS),
+		MC_CMD_INIT_TXQ_OUT_LEN);
 	efx_qword_t *dma_addr;
 	uint64_t addr;
 	int npages;
@@ -80,7 +80,6 @@
 		goto fail2;
 	}
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_INIT_TXQ;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_INIT_TXQ_IN_LEN(npages);
@@ -147,11 +146,10 @@
 	__in		uint32_t instance)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_FINI_TXQ_IN_LEN,
-			    MC_CMD_FINI_TXQ_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_FINI_TXQ_IN_LEN,
+		MC_CMD_FINI_TXQ_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_FINI_TXQ;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_FINI_TXQ_IN_LEN;
Index: head/sys/dev/sfxge/common/efx_lic.c
===================================================================
--- head/sys/dev/sfxge/common/efx_lic.c
+++ head/sys/dev/sfxge/common/efx_lic.c
@@ -328,12 +328,11 @@
 	__in		efx_nic_t *enp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MC_CMD_FC_IN_LICENSE_LEN];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_FC_IN_LICENSE_LEN, 0);
 	efx_rc_t rc;
 
 	EFSYS_ASSERT(enp->en_family == EFX_FAMILY_SIENA);
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_FC;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_FC_IN_LICENSE_LEN;
@@ -374,13 +373,12 @@
 	__out		efx_key_stats_t *eksp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_FC_IN_LICENSE_LEN,
-			    MC_CMD_FC_OUT_LICENSE_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_FC_IN_LICENSE_LEN,
+		MC_CMD_FC_OUT_LICENSE_LEN);
 	efx_rc_t rc;
 
 	EFSYS_ASSERT(enp->en_family == EFX_FAMILY_SIENA);
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_FC;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_FC_IN_LICENSE_LEN;
@@ -690,8 +688,8 @@
 	__out		boolean_t *licensedp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_LICENSED_APP_STATE_IN_LEN,
-			    MC_CMD_GET_LICENSED_APP_STATE_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_LICENSED_APP_STATE_IN_LEN,
+		MC_CMD_GET_LICENSED_APP_STATE_OUT_LEN);
 	uint32_t app_state;
 	efx_rc_t rc;
 
@@ -703,7 +701,6 @@
 		goto fail1;
 	}
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_LICENSED_APP_STATE;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_LICENSED_APP_STATE_IN_LEN;
@@ -749,12 +746,11 @@
 	__in		efx_nic_t *enp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MC_CMD_LICENSING_IN_LEN];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_LICENSING_IN_LEN, 0);
 	efx_rc_t rc;
 
 	EFSYS_ASSERT(enp->en_family == EFX_FAMILY_HUNTINGTON);
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_LICENSING;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_LICENSING_IN_LEN;
@@ -792,13 +788,12 @@
 	__out		efx_key_stats_t *eksp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_LICENSING_IN_LEN,
-			    MC_CMD_LICENSING_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_LICENSING_IN_LEN,
+		MC_CMD_LICENSING_OUT_LEN);
 	efx_rc_t rc;
 
 	EFSYS_ASSERT(enp->en_family == EFX_FAMILY_HUNTINGTON);
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_LICENSING;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_LICENSING_IN_LEN;
@@ -856,13 +851,12 @@
 	__in		efx_nic_t *enp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MC_CMD_LICENSING_V3_IN_LEN];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_LICENSING_V3_IN_LEN, 0);
 	efx_rc_t rc;
 
 	EFSYS_ASSERT((enp->en_family == EFX_FAMILY_MEDFORD) ||
 	    (enp->en_family == EFX_FAMILY_MEDFORD2));
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_LICENSING_V3;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_LICENSING_V3_IN_LEN;
@@ -893,14 +887,13 @@
 	__out		efx_key_stats_t *eksp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_LICENSING_V3_IN_LEN,
-			    MC_CMD_LICENSING_V3_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_LICENSING_V3_IN_LEN,
+		MC_CMD_LICENSING_V3_OUT_LEN);
 	efx_rc_t rc;
 
 	EFSYS_ASSERT((enp->en_family == EFX_FAMILY_MEDFORD) ||
 	    (enp->en_family == EFX_FAMILY_MEDFORD2));
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_LICENSING_V3;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_LICENSING_V3_IN_LEN;
@@ -957,15 +950,14 @@
 	__out		boolean_t *licensedp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_LICENSED_V3_APP_STATE_IN_LEN,
-			    MC_CMD_GET_LICENSED_V3_APP_STATE_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_LICENSED_V3_APP_STATE_IN_LEN,
+		MC_CMD_GET_LICENSED_V3_APP_STATE_OUT_LEN);
 	uint32_t app_state;
 	efx_rc_t rc;
 
 	EFSYS_ASSERT((enp->en_family == EFX_FAMILY_MEDFORD) ||
 	    (enp->en_family == EFX_FAMILY_MEDFORD2));
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_LICENSED_V3_APP_STATE;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_LICENSED_V3_APP_STATE_IN_LEN;
@@ -1017,8 +1009,8 @@
 			uint8_t *bufferp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_LICENSING_GET_ID_V3_IN_LEN,
-			    MC_CMD_LICENSING_GET_ID_V3_OUT_LENMIN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_LICENSING_GET_ID_V3_IN_LEN,
+		MC_CMD_LICENSING_GET_ID_V3_OUT_LENMIN);
 	efx_rc_t rc;
 
 	req.emr_cmd = MC_CMD_LICENSING_GET_ID_V3;
@@ -1029,7 +1021,6 @@
 		req.emr_in_length = MC_CMD_LICENSING_GET_ID_V3_IN_LEN;
 		req.emr_out_buf = bufferp;
 		req.emr_out_length = MC_CMD_LICENSING_GET_ID_V3_OUT_LENMIN;
-		(void) memset(payload, 0, sizeof (payload));
 	} else {
 		/* Request full buffer */
 		req.emr_in_buf = bufferp;
Index: head/sys/dev/sfxge/common/efx_mcdi.h
===================================================================
--- head/sys/dev/sfxge/common/efx_mcdi.h
+++ head/sys/dev/sfxge/common/efx_mcdi.h
@@ -412,6 +412,17 @@
 	(((mask) & (MC_CMD_PRIVILEGE_MASK_IN_GRP_ ## priv)) ==		\
 	(MC_CMD_PRIVILEGE_MASK_IN_GRP_ ## priv))
 
+/*
+ * The buffer size must be a multiple of dword to ensure that MCDI works
+ * properly with Siena based boards (which use on-chip buffer). Also, it
+ * should be at minimum the size of two dwords to allow space for extended
+ * error responses if the request/response buffer sizes are smaller.
+ */
+#define EFX_MCDI_DECLARE_BUF(_name, _in_len, _out_len)			\
+	uint8_t _name[P2ROUNDUP(MAX(MAX(_in_len, _out_len),		\
+				    (2 * sizeof (efx_dword_t))),	\
+				sizeof (efx_dword_t))] = {0}
+
 typedef enum efx_mcdi_feature_id_e {
 	EFX_MCDI_FEATURE_FW_UPDATE = 0,
 	EFX_MCDI_FEATURE_LINK_CONTROL,
Index: head/sys/dev/sfxge/common/efx_mcdi.c
===================================================================
--- head/sys/dev/sfxge/common/efx_mcdi.c
+++ head/sys/dev/sfxge/common/efx_mcdi.c
@@ -929,10 +929,10 @@
 	__out_opt		efx_mcdi_boot_t *statusp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MAX(MC_CMD_GET_VERSION_IN_LEN,
-				MC_CMD_GET_VERSION_OUT_LEN),
-			    MAX(MC_CMD_GET_BOOT_STATUS_IN_LEN,
-				MC_CMD_GET_BOOT_STATUS_OUT_LEN))];
+	EFX_MCDI_DECLARE_BUF(payload,
+		MAX(MC_CMD_GET_VERSION_IN_LEN, MC_CMD_GET_BOOT_STATUS_IN_LEN),
+		MAX(MC_CMD_GET_VERSION_OUT_LEN,
+			MC_CMD_GET_BOOT_STATUS_OUT_LEN));
 	efx_word_t *ver_words;
 	uint16_t version[4];
 	uint32_t build;
@@ -941,7 +941,6 @@
 
 	EFSYS_ASSERT3U(enp->en_features, &, EFX_FEATURE_MCDI);
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_VERSION;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_VERSION_IN_LEN;
@@ -1047,12 +1046,11 @@
 	__out_opt	uint32_t *tso2ncp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_CAPABILITIES_IN_LEN,
-			    MC_CMD_GET_CAPABILITIES_V2_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_CAPABILITIES_IN_LEN,
+		MC_CMD_GET_CAPABILITIES_V2_OUT_LEN);
 	boolean_t v2_capable;
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_CAPABILITIES;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_CAPABILITIES_IN_LEN;
@@ -1115,7 +1113,8 @@
 	__in		efx_nic_t *enp,
 	__in		boolean_t after_assertion)
 {
-	uint8_t payload[MAX(MC_CMD_REBOOT_IN_LEN, MC_CMD_REBOOT_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_REBOOT_IN_LEN,
+		MC_CMD_REBOOT_OUT_LEN);
 	efx_mcdi_req_t req;
 	efx_rc_t rc;
 
@@ -1128,7 +1127,6 @@
 	 */
 	EFSYS_ASSERT3U(enp->en_magic, ==, EFX_NIC_MAGIC);
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_REBOOT;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_REBOOT_IN_LEN;
@@ -1179,8 +1177,8 @@
 	__in		efx_nic_t *enp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_ASSERTS_IN_LEN,
-			    MC_CMD_GET_ASSERTS_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_ASSERTS_IN_LEN,
+		MC_CMD_GET_ASSERTS_OUT_LEN);
 	const char *reason;
 	unsigned int flags;
 	unsigned int index;
@@ -1281,11 +1279,10 @@
 	__in		boolean_t attach)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_DRV_ATTACH_IN_LEN,
-			    MC_CMD_DRV_ATTACH_EXT_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_DRV_ATTACH_IN_LEN,
+		MC_CMD_DRV_ATTACH_EXT_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_DRV_ATTACH;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_DRV_ATTACH_IN_LEN;
@@ -1340,11 +1337,10 @@
 {
 	efx_mcdi_iface_t *emip = &(enp->en_mcdi.em_emip);
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_BOARD_CFG_IN_LEN,
-			    MC_CMD_GET_BOARD_CFG_OUT_LENMIN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_BOARD_CFG_IN_LEN,
+		MC_CMD_GET_BOARD_CFG_OUT_LENMIN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_BOARD_CFG;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_BOARD_CFG_IN_LEN;
@@ -1420,11 +1416,10 @@
 	__out_opt	uint32_t *ntxqp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_RESOURCE_LIMITS_IN_LEN,
-			    MC_CMD_GET_RESOURCE_LIMITS_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_RESOURCE_LIMITS_IN_LEN,
+		MC_CMD_GET_RESOURCE_LIMITS_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_RESOURCE_LIMITS;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_RESOURCE_LIMITS_IN_LEN;
@@ -1467,8 +1462,8 @@
 	efx_port_t *epp = &(enp->en_port);
 	efx_nic_cfg_t *encp = &(enp->en_nic_cfg);
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_PHY_CFG_IN_LEN,
-			    MC_CMD_GET_PHY_CFG_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_PHY_CFG_IN_LEN,
+		MC_CMD_GET_PHY_CFG_OUT_LEN);
 #if EFSYS_OPT_NAMES
 	const char *namep;
 	size_t namelen;
@@ -1476,7 +1471,6 @@
 	uint32_t phy_media_type;
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_PHY_CFG;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_PHY_CFG_IN_LEN;
@@ -1715,11 +1709,10 @@
 	__in			efx_bist_type_t type)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_START_BIST_IN_LEN,
-			    MC_CMD_START_BIST_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_START_BIST_IN_LEN,
+		MC_CMD_START_BIST_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_START_BIST;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_START_BIST_IN_LEN;
@@ -1778,11 +1771,10 @@
 	__in		efx_nic_t *enp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_LOG_CTRL_IN_LEN,
-			    MC_CMD_LOG_CTRL_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_LOG_CTRL_IN_LEN,
+		MC_CMD_LOG_CTRL_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_LOG_CTRL;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_LOG_CTRL_IN_LEN;
@@ -1827,8 +1819,8 @@
 	__in		uint16_t period_ms)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_MAC_STATS_IN_LEN,
-			    MC_CMD_MAC_STATS_V2_OUT_DMA_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_MAC_STATS_IN_LEN,
+		MC_CMD_MAC_STATS_V2_OUT_DMA_LEN);
 	int clear = (action == EFX_STATS_CLEAR);
 	int upload = (action == EFX_STATS_UPLOAD);
 	int enable = (action == EFX_STATS_ENABLE_NOEVENTS);
@@ -1836,7 +1828,6 @@
 	int disable = (action == EFX_STATS_DISABLE);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_MAC_STATS;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_MAC_STATS_IN_LEN;
@@ -2008,11 +1999,10 @@
 	__out_opt		uint32_t *vfp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_FUNCTION_INFO_IN_LEN,
-			    MC_CMD_GET_FUNCTION_INFO_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_FUNCTION_INFO_IN_LEN,
+		MC_CMD_GET_FUNCTION_INFO_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_FUNCTION_INFO;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_FUNCTION_INFO_IN_LEN;
@@ -2053,11 +2043,10 @@
 	__out			uint32_t *maskp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_PRIVILEGE_MASK_IN_LEN,
-			    MC_CMD_PRIVILEGE_MASK_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_PRIVILEGE_MASK_IN_LEN,
+		MC_CMD_PRIVILEGE_MASK_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_PRIVILEGE_MASK;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_PRIVILEGE_MASK_IN_LEN;
@@ -2102,11 +2091,10 @@
 	__out_opt		uint32_t *flagsp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_WORKAROUND_IN_LEN,
-			    MC_CMD_WORKAROUND_EXT_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_WORKAROUND_IN_LEN,
+		MC_CMD_WORKAROUND_EXT_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_WORKAROUND;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_WORKAROUND_IN_LEN;
@@ -2146,10 +2134,9 @@
 	__out_opt		uint32_t *enabledp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MC_CMD_GET_WORKAROUNDS_OUT_LEN];
+	EFX_MCDI_DECLARE_BUF(payload, 0, MC_CMD_GET_WORKAROUNDS_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_WORKAROUNDS;
 	req.emr_in_buf = NULL;
 	req.emr_in_length = 0;
@@ -2195,14 +2182,13 @@
 	__out_bcount(len)	uint8_t *data)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_PHY_MEDIA_INFO_IN_LEN,
-			    MC_CMD_GET_PHY_MEDIA_INFO_OUT_LEN(
-				EFX_PHY_MEDIA_INFO_PAGE_SIZE))];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_PHY_MEDIA_INFO_IN_LEN,
+		MC_CMD_GET_PHY_MEDIA_INFO_OUT_LEN(
+			EFX_PHY_MEDIA_INFO_PAGE_SIZE));
 	efx_rc_t rc;
 
 	EFSYS_ASSERT((uint32_t)offset + len <= EFX_PHY_MEDIA_INFO_PAGE_SIZE);
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_PHY_MEDIA_INFO;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_PHY_MEDIA_INFO_IN_LEN;
Index: head/sys/dev/sfxge/common/efx_nic.c
===================================================================
--- head/sys/dev/sfxge/common/efx_nic.c
+++ head/sys/dev/sfxge/common/efx_nic.c
@@ -818,13 +818,12 @@
 {
 	efx_nic_cfg_t *encp = &(enp->en_nic_cfg);
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_LOOPBACK_MODES_IN_LEN,
-			    MC_CMD_GET_LOOPBACK_MODES_OUT_V2_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_LOOPBACK_MODES_IN_LEN,
+		MC_CMD_GET_LOOPBACK_MODES_OUT_V2_LEN);
 	efx_qword_t mask;
 	efx_qword_t modes;
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_LOOPBACK_MODES;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_LOOPBACK_MODES_IN_LEN;
Index: head/sys/dev/sfxge/common/efx_nvram.c
===================================================================
--- head/sys/dev/sfxge/common/efx_nvram.c
+++ head/sys/dev/sfxge/common/efx_nvram.c
@@ -543,12 +543,11 @@
 	__out			unsigned int *npartnp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_NVRAM_PARTITIONS_IN_LEN,
-			    MC_CMD_NVRAM_PARTITIONS_OUT_LENMAX)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_NVRAM_PARTITIONS_IN_LEN,
+		MC_CMD_NVRAM_PARTITIONS_OUT_LENMAX);
 	unsigned int npartn;
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_NVRAM_PARTITIONS;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_NVRAM_PARTITIONS_IN_LEN;
@@ -606,11 +605,10 @@
 	__in			size_t size)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_NVRAM_METADATA_IN_LEN,
-			    MC_CMD_NVRAM_METADATA_OUT_LENMAX)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_NVRAM_METADATA_IN_LEN,
+		MC_CMD_NVRAM_METADATA_OUT_LENMAX);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_NVRAM_METADATA;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_NVRAM_METADATA_IN_LEN;
@@ -696,12 +694,11 @@
 	__out_opt		uint32_t *erase_sizep,
 	__out_opt		uint32_t *write_sizep)
 {
-	uint8_t payload[MAX(MC_CMD_NVRAM_INFO_IN_LEN,
-			    MC_CMD_NVRAM_INFO_V2_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_NVRAM_INFO_IN_LEN,
+		MC_CMD_NVRAM_INFO_V2_OUT_LEN);
 	efx_mcdi_req_t req;
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_NVRAM_INFO;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_NVRAM_INFO_IN_LEN;
@@ -757,12 +754,11 @@
 	__in			efx_nic_t *enp,
 	__in			uint32_t partn)
 {
-	uint8_t payload[MAX(MC_CMD_NVRAM_UPDATE_START_V2_IN_LEN,
-			    MC_CMD_NVRAM_UPDATE_START_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_NVRAM_UPDATE_START_V2_IN_LEN,
+		MC_CMD_NVRAM_UPDATE_START_OUT_LEN);
 	efx_mcdi_req_t req;
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_NVRAM_UPDATE_START;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_NVRAM_UPDATE_START_V2_IN_LEN;
@@ -799,8 +795,8 @@
 	__in			uint32_t mode)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_NVRAM_READ_IN_V2_LEN,
-			    MC_CMD_NVRAM_READ_OUT_LENMAX)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_NVRAM_READ_IN_V2_LEN,
+		MC_CMD_NVRAM_READ_OUT_LENMAX);
 	efx_rc_t rc;
 
 	if (size > MC_CMD_NVRAM_READ_OUT_LENMAX) {
@@ -808,7 +804,6 @@
 		goto fail1;
 	}
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_NVRAM_READ;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_NVRAM_READ_IN_V2_LEN;
@@ -854,11 +849,10 @@
 	__in			size_t size)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_NVRAM_ERASE_IN_LEN,
-			    MC_CMD_NVRAM_ERASE_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_NVRAM_ERASE_IN_LEN,
+		MC_CMD_NVRAM_ERASE_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_NVRAM_ERASE;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_NVRAM_ERASE_IN_LEN;
@@ -968,12 +962,11 @@
 {
 	const efx_nic_cfg_t *encp = &enp->en_nic_cfg;
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_NVRAM_UPDATE_FINISH_V2_IN_LEN,
-			    MC_CMD_NVRAM_UPDATE_FINISH_V2_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_NVRAM_UPDATE_FINISH_V2_IN_LEN,
+		MC_CMD_NVRAM_UPDATE_FINISH_V2_OUT_LEN);
 	uint32_t verify_result = MC_CMD_NVRAM_VERIFY_RC_UNKNOWN;
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_NVRAM_UPDATE_FINISH;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_NVRAM_UPDATE_FINISH_V2_IN_LEN;
@@ -1039,12 +1032,11 @@
 	__in			uint32_t partn)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_NVRAM_TEST_IN_LEN,
-			    MC_CMD_NVRAM_TEST_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_NVRAM_TEST_IN_LEN,
+		MC_CMD_NVRAM_TEST_OUT_LEN);
 	int result;
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_NVRAM_TEST;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_NVRAM_TEST_IN_LEN;
Index: head/sys/dev/sfxge/common/efx_tunnel.c
===================================================================
--- head/sys/dev/sfxge/common/efx_tunnel.c
+++ head/sys/dev/sfxge/common/efx_tunnel.c
@@ -69,8 +69,9 @@
 	__out			boolean_t *resetting)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_SET_TUNNEL_ENCAP_UDP_PORTS_IN_LENMAX,
-			    MC_CMD_SET_TUNNEL_ENCAP_UDP_PORTS_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload,
+		MC_CMD_SET_TUNNEL_ENCAP_UDP_PORTS_IN_LENMAX,
+		MC_CMD_SET_TUNNEL_ENCAP_UDP_PORTS_OUT_LEN);
 	efx_word_t flags;
 	efx_rc_t rc;
 	unsigned int i;
@@ -81,7 +82,6 @@
 	else
 		entries_num = etcp->etc_udp_entries_num;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_SET_TUNNEL_ENCAP_UDP_PORTS;
 	req.emr_in_buf = payload;
 	req.emr_in_length =
Index: head/sys/dev/sfxge/common/mcdi_mon.c
===================================================================
--- head/sys/dev/sfxge/common/mcdi_mon.c
+++ head/sys/dev/sfxge/common/mcdi_mon.c
@@ -218,8 +218,8 @@
 	__in		uint32_t size)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_READ_SENSORS_EXT_IN_LEN,
-			    MC_CMD_READ_SENSORS_EXT_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_READ_SENSORS_EXT_IN_LEN,
+		MC_CMD_READ_SENSORS_EXT_OUT_LEN);
 	uint32_t addr_lo, addr_hi;
 	efx_rc_t rc;
 
@@ -257,8 +257,8 @@
 	__out		uint32_t *npagesp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_SENSOR_INFO_EXT_IN_LEN,
-			    MC_CMD_SENSOR_INFO_OUT_LENMAX)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_SENSOR_INFO_EXT_IN_LEN,
+		MC_CMD_SENSOR_INFO_OUT_LENMAX);
 	int page;
 	efx_rc_t rc;
 
@@ -301,8 +301,8 @@
 	__in			size_t npages)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_SENSOR_INFO_EXT_IN_LEN,
-			    MC_CMD_SENSOR_INFO_OUT_LENMAX)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_SENSOR_INFO_EXT_IN_LEN,
+		MC_CMD_SENSOR_INFO_OUT_LENMAX);
 	uint32_t page;
 	efx_rc_t rc;
 
@@ -370,8 +370,8 @@
 				efx_mon_stat_limits_t *limits)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_SENSOR_INFO_EXT_IN_LEN,
-		MC_CMD_SENSOR_INFO_OUT_LENMAX)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_SENSOR_INFO_EXT_IN_LEN,
+		MC_CMD_SENSOR_INFO_OUT_LENMAX);
 	efx_rc_t rc;
 	uint32_t mask_copy;
 	efx_dword_t *maskp;
@@ -383,7 +383,6 @@
 	memset(limits, 0,
 	    ((sizeof (*mask_part) * 8) - 1) * sizeof (efx_mon_stat_limits_t));
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_SENSOR_INFO;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_SENSOR_INFO_EXT_IN_LEN;
Index: head/sys/dev/sfxge/common/siena_mac.c
===================================================================
--- head/sys/dev/sfxge/common/siena_mac.c
+++ head/sys/dev/sfxge/common/siena_mac.c
@@ -97,14 +97,13 @@
 	efx_port_t *epp = &(enp->en_port);
 	efx_oword_t multicast_hash[2];
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MAX(MC_CMD_SET_MAC_IN_LEN,
-				MC_CMD_SET_MAC_OUT_LEN),
-			    MAX(MC_CMD_SET_MCAST_HASH_IN_LEN,
-				MC_CMD_SET_MCAST_HASH_OUT_LEN))];
+	EFX_MCDI_DECLARE_BUF(payload,
+		MAX(MC_CMD_SET_MAC_IN_LEN, MC_CMD_SET_MCAST_HASH_IN_LEN),
+		MAX(MC_CMD_SET_MAC_OUT_LEN, MC_CMD_SET_MCAST_HASH_OUT_LEN));
+
 	unsigned int fcntl;
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_SET_MAC;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_SET_MAC_IN_LEN;
Index: head/sys/dev/sfxge/common/siena_nic.c
===================================================================
--- head/sys/dev/sfxge/common/siena_nic.c
+++ head/sys/dev/sfxge/common/siena_nic.c
@@ -47,11 +47,10 @@
 	__out			unsigned int *maskp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_NVRAM_TYPES_IN_LEN,
-			    MC_CMD_NVRAM_TYPES_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_NVRAM_TYPES_IN_LEN,
+		MC_CMD_NVRAM_TYPES_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_NVRAM_TYPES;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_NVRAM_TYPES_IN_LEN;
Index: head/sys/dev/sfxge/common/siena_nvram.c
===================================================================
--- head/sys/dev/sfxge/common/siena_nvram.c
+++ head/sys/dev/sfxge/common/siena_nvram.c
@@ -447,12 +447,11 @@
 	__out			uint32_t *subtypep)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_BOARD_CFG_IN_LEN,
-			    MC_CMD_GET_BOARD_CFG_OUT_LENMAX)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_BOARD_CFG_IN_LEN,
+		MC_CMD_GET_BOARD_CFG_OUT_LENMAX);
 	efx_word_t *fw_list;
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_BOARD_CFG;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_BOARD_CFG_IN_LEN;
Index: head/sys/dev/sfxge/common/siena_phy.c
===================================================================
--- head/sys/dev/sfxge/common/siena_phy.c
+++ head/sys/dev/sfxge/common/siena_phy.c
@@ -198,11 +198,10 @@
 	__out		siena_link_state_t *slsp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_LINK_IN_LEN,
-			    MC_CMD_GET_LINK_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_LINK_IN_LEN,
+		MC_CMD_GET_LINK_OUT_LEN);
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_LINK;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_LINK_IN_LEN;
@@ -273,10 +272,9 @@
 {
 	efx_port_t *epp = &(enp->en_port);
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MAX(MC_CMD_SET_ID_LED_IN_LEN,
-				MC_CMD_SET_ID_LED_OUT_LEN),
-			    MAX(MC_CMD_SET_LINK_IN_LEN,
-				MC_CMD_SET_LINK_OUT_LEN))];
+	EFX_MCDI_DECLARE_BUF(payload,
+		MAX(MC_CMD_SET_ID_LED_IN_LEN, MC_CMD_SET_LINK_IN_LEN),
+		MAX(MC_CMD_SET_ID_LED_OUT_LEN, MC_CMD_SET_LINK_OUT_LEN));
 	uint32_t cap_mask;
 #if EFSYS_OPT_PHY_LED_CONTROL
 	unsigned int led_mode;
@@ -284,7 +282,6 @@
 	unsigned int speed;
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_SET_LINK;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_SET_LINK_IN_LEN;
@@ -390,12 +387,11 @@
 	__in		efx_nic_t *enp)
 {
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_GET_PHY_STATE_IN_LEN,
-			    MC_CMD_GET_PHY_STATE_OUT_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_GET_PHY_STATE_IN_LEN,
+		MC_CMD_GET_PHY_STATE_OUT_LEN);
 	uint32_t state;
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_GET_PHY_STATE;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_GET_PHY_STATE_IN_LEN;
@@ -559,8 +555,8 @@
 	uint32_t vmask = encp->enc_mcdi_phy_stat_mask;
 	uint64_t smask;
 	efx_mcdi_req_t req;
-	uint8_t payload[MAX(MC_CMD_PHY_STATS_IN_LEN,
-			    MC_CMD_PHY_STATS_OUT_DMA_LEN)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_PHY_STATS_IN_LEN,
+		MC_CMD_PHY_STATS_OUT_DMA_LEN);
 	efx_rc_t rc;
 
 	if ((esmp == NULL) || (EFSYS_MEM_SIZE(esmp) < EFX_PHY_STATS_SIZE)) {
@@ -568,7 +564,6 @@
 		goto fail1;
 	}
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_PHY_STATS;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_PHY_STATS_IN_LEN;
@@ -655,14 +650,13 @@
 	__in			size_t count)
 {
 	efx_nic_cfg_t *encp = &(enp->en_nic_cfg);
-	uint8_t payload[MAX(MC_CMD_POLL_BIST_IN_LEN,
-			    MCDI_CTL_SDU_LEN_MAX)];
+	EFX_MCDI_DECLARE_BUF(payload, MC_CMD_POLL_BIST_IN_LEN,
+		MCDI_CTL_SDU_LEN_MAX);
 	uint32_t value_mask = 0;
 	efx_mcdi_req_t req;
 	uint32_t result;
 	efx_rc_t rc;
 
-	(void) memset(payload, 0, sizeof (payload));
 	req.emr_cmd = MC_CMD_POLL_BIST;
 	req.emr_in_buf = payload;
 	req.emr_in_length = MC_CMD_POLL_BIST_IN_LEN;