diff --git a/drivers/net/sfc/base/ef10_ev.c b/drivers/net/sfc/base/ef10_ev.c
index 7f89a7bf0..287550605 100644
--- a/drivers/net/sfc/base/ef10_ev.c
+++ b/drivers/net/sfc/base/ef10_ev.c
@@ -73,11 +73,10 @@ efx_mcdi_set_evq_tmr(
 	__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;
@@ -123,9 +122,9 @@ efx_mcdi_init_evq(
 	__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;
@@ -140,7 +139,6 @@ efx_mcdi_init_evq(
 		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);
@@ -260,9 +258,9 @@ efx_mcdi_init_evq_v2(
 	__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;
@@ -277,7 +275,6 @@ efx_mcdi_init_evq_v2(
 		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);
@@ -384,11 +381,10 @@ efx_mcdi_fini_evq(
 	__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;
@@ -603,8 +599,8 @@ efx_mcdi_driver_event(
 	__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;
diff --git a/drivers/net/sfc/base/ef10_filter.c b/drivers/net/sfc/base/ef10_filter.c
index a4d97f99c..30a4892df 100644
--- a/drivers/net/sfc/base/ef10_filter.c
+++ b/drivers/net/sfc/base/ef10_filter.c
@@ -172,12 +172,11 @@ efx_mcdi_filter_op_add(
 	__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;
@@ -376,11 +375,10 @@ efx_mcdi_filter_op_delete(
 	__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;
@@ -950,13 +948,12 @@ efx_mcdi_get_parser_disp_info(
 	__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;
diff --git a/drivers/net/sfc/base/ef10_intr.c b/drivers/net/sfc/base/ef10_intr.c
index 1ffe266b1..efa157125 100644
--- a/drivers/net/sfc/base/ef10_intr.c
+++ b/drivers/net/sfc/base/ef10_intr.c
@@ -51,8 +51,8 @@ efx_mcdi_trigger_interrupt(
 	__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 ||
@@ -64,7 +64,6 @@ efx_mcdi_trigger_interrupt(
 		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;
diff --git a/drivers/net/sfc/base/ef10_mac.c b/drivers/net/sfc/base/ef10_mac.c
index c14010732..a4a6d9ec8 100644
--- a/drivers/net/sfc/base/ef10_mac.c
+++ b/drivers/net/sfc/base/ef10_mac.c
@@ -75,11 +75,10 @@ efx_mcdi_vadapter_set_mac(
 {
 	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;
@@ -141,11 +140,10 @@ efx_mcdi_mtu_set(
 	__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;
@@ -178,11 +176,10 @@ efx_mcdi_mtu_get(
 	__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;
@@ -274,11 +271,10 @@ ef10_mac_reconfigure(
 {
 	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;
diff --git a/drivers/net/sfc/base/ef10_nic.c b/drivers/net/sfc/base/ef10_nic.c
index 9145c389c..332f6ef81 100644
--- a/drivers/net/sfc/base/ef10_nic.c
+++ b/drivers/net/sfc/base/ef10_nic.c
@@ -20,15 +20,14 @@ efx_mcdi_get_port_assignment(
 	__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;
@@ -67,15 +66,14 @@ efx_mcdi_get_port_modes(
 	__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;
@@ -180,13 +178,12 @@ efx_mcdi_vadaptor_alloc(
 	__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;
@@ -219,11 +216,10 @@ efx_mcdi_vadaptor_free(
 	__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;
@@ -253,15 +249,14 @@ efx_mcdi_get_mac_address_pf(
 	__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;
@@ -312,15 +307,14 @@ efx_mcdi_get_mac_address_vf(
 	__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;
@@ -377,15 +371,14 @@ efx_mcdi_get_clock(
 	__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;
@@ -435,12 +428,11 @@ efx_mcdi_get_rxdp_config(
 	__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;
@@ -495,11 +487,10 @@ efx_mcdi_get_vector_cfg(
 	__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;
@@ -545,8 +536,8 @@ efx_mcdi_alloc_vis(
 	__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) {
@@ -554,7 +545,6 @@ efx_mcdi_alloc_vis(
 		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;
@@ -637,8 +627,8 @@ efx_mcdi_alloc_piobuf(
 	__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) {
@@ -646,7 +636,6 @@ efx_mcdi_alloc_piobuf(
 		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;
@@ -685,11 +674,10 @@ efx_mcdi_free_piobuf(
 	__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;
@@ -720,11 +708,10 @@ efx_mcdi_link_piobuf(
 	__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;
@@ -755,11 +742,10 @@ efx_mcdi_unlink_piobuf(
 	__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;
@@ -957,11 +943,10 @@ ef10_mcdi_get_pf_count(
 	__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;
@@ -1001,15 +986,14 @@ ef10_get_datapath_caps(
 {
 	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;
@@ -2046,8 +2030,8 @@ ef10_nic_reset(
 	__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. */
@@ -2056,7 +2040,6 @@ ef10_nic_reset(
 	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;
@@ -2393,11 +2376,10 @@ efx_mcdi_get_nic_global(
 	__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;
@@ -2437,10 +2419,9 @@ efx_mcdi_set_nic_global(
 	__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;
diff --git a/drivers/net/sfc/base/ef10_phy.c b/drivers/net/sfc/base/ef10_phy.c
index e9c7b40e4..a1f59ff1c 100644
--- a/drivers/net/sfc/base/ef10_phy.c
+++ b/drivers/net/sfc/base/ef10_phy.c
@@ -242,11 +242,10 @@ ef10_phy_get_link(
 	__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;
@@ -301,8 +300,8 @@ ef10_phy_reconfigure(
 {
 	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;
@@ -316,7 +315,6 @@ ef10_phy_reconfigure(
 	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;
@@ -464,12 +462,11 @@ ef10_phy_verify(
 	__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;
@@ -587,7 +584,8 @@ ef10_bist_poll(
 	 * 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;
@@ -605,7 +603,6 @@ ef10_bist_poll(
 
 	_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;
diff --git a/drivers/net/sfc/base/ef10_rx.c b/drivers/net/sfc/base/ef10_rx.c
index 313a36918..17678b517 100644
--- a/drivers/net/sfc/base/ef10_rx.c
+++ b/drivers/net/sfc/base/ef10_rx.c
@@ -29,8 +29,8 @@ efx_mcdi_init_rxq(
 {
 	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;
@@ -73,7 +73,6 @@ efx_mcdi_init_rxq(
 		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;
@@ -146,11 +145,10 @@ efx_mcdi_fini_rxq(
 	__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;
@@ -188,8 +186,8 @@ efx_mcdi_rss_context_alloc(
 	__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;
@@ -211,7 +209,6 @@ efx_mcdi_rss_context_alloc(
 		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;
@@ -274,8 +271,8 @@ efx_mcdi_rss_context_free(
 	__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) {
@@ -283,7 +280,6 @@ efx_mcdi_rss_context_free(
 		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;
@@ -324,8 +320,8 @@ efx_mcdi_rss_context_set_flags(
 	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 ==
@@ -350,7 +346,6 @@ efx_mcdi_rss_context_set_flags(
 		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;
@@ -439,8 +434,8 @@ efx_mcdi_rss_context_set_key(
 	__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) {
@@ -448,7 +443,6 @@ efx_mcdi_rss_context_set_key(
 		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;
@@ -496,8 +490,8 @@ efx_mcdi_rss_context_set_table(
 	__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;
 
@@ -506,7 +500,6 @@ efx_mcdi_rss_context_set_table(
 		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;
diff --git a/drivers/net/sfc/base/ef10_tx.c b/drivers/net/sfc/base/ef10_tx.c
index 4d77d76d7..5f3df42b9 100644
--- a/drivers/net/sfc/base/ef10_tx.c
+++ b/drivers/net/sfc/base/ef10_tx.c
@@ -31,8 +31,8 @@ efx_mcdi_init_txq(
 	__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;
@@ -53,7 +53,6 @@ efx_mcdi_init_txq(
 		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);
@@ -120,11 +119,10 @@ efx_mcdi_fini_txq(
 	__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;
diff --git a/drivers/net/sfc/base/efx_lic.c b/drivers/net/sfc/base/efx_lic.c
index 2b06e2d1e..2a6da2647 100644
--- a/drivers/net/sfc/base/efx_lic.c
+++ b/drivers/net/sfc/base/efx_lic.c
@@ -301,12 +301,11 @@ efx_mcdi_fc_license_update_license(
 	__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;
@@ -347,13 +346,12 @@ efx_mcdi_fc_license_get_key_stats(
 	__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;
@@ -663,8 +661,8 @@ efx_mcdi_licensed_app_state(
 	__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;
 
@@ -676,7 +674,6 @@ efx_mcdi_licensed_app_state(
 		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;
@@ -722,12 +719,11 @@ efx_mcdi_licensing_update_licenses(
 	__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;
@@ -765,13 +761,12 @@ efx_mcdi_licensing_get_key_stats(
 	__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;
@@ -829,13 +824,12 @@ efx_mcdi_licensing_v3_update_licenses(
 	__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;
@@ -866,14 +860,13 @@ efx_mcdi_licensing_v3_report_license(
 	__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;
@@ -930,15 +923,14 @@ efx_mcdi_licensing_v3_app_state(
 	__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;
@@ -990,8 +982,8 @@ efx_mcdi_licensing_v3_get_id(
 			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;
@@ -1002,7 +994,6 @@ efx_mcdi_licensing_v3_get_id(
 		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;
diff --git a/drivers/net/sfc/base/efx_mcdi.c b/drivers/net/sfc/base/efx_mcdi.c
index d4ebcf265..84d8452e4 100644
--- a/drivers/net/sfc/base/efx_mcdi.c
+++ b/drivers/net/sfc/base/efx_mcdi.c
@@ -900,10 +900,10 @@ efx_mcdi_version(
 	__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;
@@ -912,7 +912,6 @@ efx_mcdi_version(
 
 	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;
@@ -1018,12 +1017,11 @@ efx_mcdi_get_capabilities(
 	__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;
@@ -1086,7 +1084,8 @@ efx_mcdi_do_reboot(
 	__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;
 
@@ -1099,7 +1098,6 @@ efx_mcdi_do_reboot(
 	 */
 	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;
@@ -1150,8 +1148,8 @@ efx_mcdi_read_assertion(
 	__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;
@@ -1252,11 +1250,10 @@ efx_mcdi_drv_attach(
 	__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;
@@ -1311,11 +1308,10 @@ efx_mcdi_get_board_cfg(
 {
 	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;
@@ -1391,11 +1387,10 @@ efx_mcdi_get_resource_limits(
 	__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;
@@ -1438,8 +1433,8 @@ efx_mcdi_get_phy_cfg(
 	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;
@@ -1447,7 +1442,6 @@ efx_mcdi_get_phy_cfg(
 	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;
@@ -1686,11 +1680,10 @@ efx_mcdi_bist_start(
 	__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;
@@ -1749,11 +1742,10 @@ efx_mcdi_log_ctrl(
 	__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;
@@ -1798,8 +1790,8 @@ efx_mcdi_mac_stats(
 	__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);
@@ -1807,7 +1799,6 @@ efx_mcdi_mac_stats(
 	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;
@@ -1979,11 +1970,10 @@ efx_mcdi_get_function_info(
 	__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;
@@ -2024,11 +2014,10 @@ efx_mcdi_privilege_mask(
 	__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;
@@ -2073,11 +2062,10 @@ efx_mcdi_set_workaround(
 	__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;
@@ -2117,10 +2105,9 @@ efx_mcdi_get_workarounds(
 	__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;
@@ -2166,14 +2153,13 @@ efx_mcdi_get_phy_media_info(
 	__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;
diff --git a/drivers/net/sfc/base/efx_mcdi.h b/drivers/net/sfc/base/efx_mcdi.h
index d2cd1e9e1..40072405e 100644
--- a/drivers/net/sfc/base/efx_mcdi.h
+++ b/drivers/net/sfc/base/efx_mcdi.h
@@ -384,6 +384,17 @@ efx_mcdi_phy_module_get_info(
 	(((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,
diff --git a/drivers/net/sfc/base/efx_nic.c b/drivers/net/sfc/base/efx_nic.c
index 0e8ed9c2a..c364bffba 100644
--- a/drivers/net/sfc/base/efx_nic.c
+++ b/drivers/net/sfc/base/efx_nic.c
@@ -789,13 +789,12 @@ efx_mcdi_get_loopback_modes(
 {
 	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;
diff --git a/drivers/net/sfc/base/efx_nvram.c b/drivers/net/sfc/base/efx_nvram.c
index d7b1a6778..5296c59b8 100644
--- a/drivers/net/sfc/base/efx_nvram.c
+++ b/drivers/net/sfc/base/efx_nvram.c
@@ -514,12 +514,11 @@ efx_mcdi_nvram_partitions(
 	__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;
@@ -577,11 +576,10 @@ efx_mcdi_nvram_metadata(
 	__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;
@@ -667,12 +665,11 @@ efx_mcdi_nvram_info(
 	__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;
@@ -728,12 +725,11 @@ efx_mcdi_nvram_update_start(
 	__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;
@@ -770,8 +766,8 @@ efx_mcdi_nvram_read(
 	__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) {
@@ -779,7 +775,6 @@ efx_mcdi_nvram_read(
 		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;
@@ -825,11 +820,10 @@ efx_mcdi_nvram_erase(
 	__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;
@@ -939,12 +933,11 @@ efx_mcdi_nvram_update_finish(
 {
 	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;
@@ -1010,12 +1003,11 @@ efx_mcdi_nvram_test(
 	__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;
diff --git a/drivers/net/sfc/base/efx_tunnel.c b/drivers/net/sfc/base/efx_tunnel.c
index 399fd540b..edb6be028 100644
--- a/drivers/net/sfc/base/efx_tunnel.c
+++ b/drivers/net/sfc/base/efx_tunnel.c
@@ -40,8 +40,9 @@ efx_mcdi_set_tunnel_encap_udp_ports(
 	__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;
@@ -52,7 +53,6 @@ efx_mcdi_set_tunnel_encap_udp_ports(
 	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 =
diff --git a/drivers/net/sfc/base/mcdi_mon.c b/drivers/net/sfc/base/mcdi_mon.c
index 0e860168a..b53de0d68 100644
--- a/drivers/net/sfc/base/mcdi_mon.c
+++ b/drivers/net/sfc/base/mcdi_mon.c
@@ -191,8 +191,8 @@ efx_mcdi_read_sensors(
 	__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;
 
@@ -230,8 +230,8 @@ efx_mcdi_sensor_info_npages(
 	__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;
 
@@ -274,8 +274,8 @@ efx_mcdi_sensor_info(
 	__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;
 
@@ -343,8 +343,8 @@ efx_mcdi_sensor_info_page(
 				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;
@@ -356,7 +356,6 @@ efx_mcdi_sensor_info_page(
 	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;
diff --git a/drivers/net/sfc/base/siena_mac.c b/drivers/net/sfc/base/siena_mac.c
index f8857cdd5..928dfc340 100644
--- a/drivers/net/sfc/base/siena_mac.c
+++ b/drivers/net/sfc/base/siena_mac.c
@@ -68,14 +68,13 @@ siena_mac_reconfigure(
 	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;
diff --git a/drivers/net/sfc/base/siena_nic.c b/drivers/net/sfc/base/siena_nic.c
index 31eef80b9..8a58986e8 100644
--- a/drivers/net/sfc/base/siena_nic.c
+++ b/drivers/net/sfc/base/siena_nic.c
@@ -18,11 +18,10 @@ siena_nic_get_partn_mask(
 	__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;
diff --git a/drivers/net/sfc/base/siena_nvram.c b/drivers/net/sfc/base/siena_nvram.c
index 8cdd2df70..b8ea8a757 100644
--- a/drivers/net/sfc/base/siena_nvram.c
+++ b/drivers/net/sfc/base/siena_nvram.c
@@ -418,12 +418,11 @@ siena_nvram_get_subtype(
 	__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;
diff --git a/drivers/net/sfc/base/siena_phy.c b/drivers/net/sfc/base/siena_phy.c
index 4b2190d38..7eec9c747 100644
--- a/drivers/net/sfc/base/siena_phy.c
+++ b/drivers/net/sfc/base/siena_phy.c
@@ -169,11 +169,10 @@ siena_phy_get_link(
 	__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;
@@ -244,10 +243,9 @@ siena_phy_reconfigure(
 {
 	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;
@@ -255,7 +253,6 @@ siena_phy_reconfigure(
 	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;
@@ -361,12 +358,11 @@ siena_phy_verify(
 	__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;
@@ -530,8 +526,8 @@ siena_phy_stats_update(
 	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)) {
@@ -539,7 +535,6 @@ siena_phy_stats_update(
 		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;
@@ -626,14 +621,13 @@ siena_phy_bist_poll(
 	__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;
