mlxsw: Add bus capability flag

The mlxsw core infrastructure currently assumes that communication with
the ASIC is always possible using Ethernet management datagrams (EMADs),
but this is only possible when the PCI bus is used.

The bus capability flag is added to indicate EMAD support and make core
initialize EMAD communication only when it's set. Otherwise, register
access is done using command interface.

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/core.c

@@ -598,6 +598,9 @@ static int mlxsw_emad_init(struct mlxsw_core *mlxsw_core)
 	u64 tid;
 	int err;
 
+	if (!(mlxsw_core->bus->features & MLXSW_BUS_F_TXRX))
+		return 0;
+
 	/* Set the upper 32 bits of the transaction ID field to a random
 	 * number. This allows us to discard EMADs addressed to other
 	 * devices.
@@ -634,6 +637,9 @@ static void mlxsw_emad_fini(struct mlxsw_core *mlxsw_core)
 {
 	char hpkt_pl[MLXSW_REG_HPKT_LEN];
 
+	if (!(mlxsw_core->bus->features & MLXSW_BUS_F_TXRX))
+		return;
+
 	mlxsw_core->emad.use_emad = false;
 	mlxsw_reg_hpkt_pack(hpkt_pl, MLXSW_REG_HPKT_ACTION_DISCARD,
 			    MLXSW_TRAP_ID_ETHEMAD);

drivers/net/ethernet/mellanox/mlxsw/core.h

@@ -268,6 +268,8 @@ u64 mlxsw_core_res_get(struct mlxsw_core *mlxsw_core,
 #define MLXSW_CORE_RES_GET(res, short_res_id)			\
 	mlxsw_core_res_get(res, MLXSW_RES_ID_##short_res_id)
 
+#define MLXSW_BUS_F_TXRX	BIT(0)
+
 struct mlxsw_bus {
 	const char *kind;
 	int (*init)(void *bus_priv, struct mlxsw_core *mlxsw_core,
@@ -283,6 +285,7 @@ struct mlxsw_bus {
 			char *in_mbox, size_t in_mbox_size,
 			char *out_mbox, size_t out_mbox_size,
 			u8 *p_status);
+	u8 features;
 };
 
 struct mlxsw_bus_info {

drivers/net/ethernet/mellanox/mlxsw/pci.c

@@ -1755,6 +1755,7 @@ static const struct mlxsw_bus mlxsw_pci_bus = {
 	.skb_transmit_busy	= mlxsw_pci_skb_transmit_busy,
 	.skb_transmit		= mlxsw_pci_skb_transmit,
 	.cmd_exec		= mlxsw_pci_cmd_exec,
+	.features		= MLXSW_BUS_F_TXRX,
 };
 
 static int mlxsw_pci_sw_reset(struct mlxsw_pci *mlxsw_pci,