net/mlx5: Do not query MPIR on embedded CPU function

A proper query to MPIR needs to set the correct value in the depth field.
On embedded CPU this value is not necessarily zero. As there is no real
use case for multi-PF netdev on the embedded CPU of the smart NIC, block
this option.

This fixes the following failure:
ACCESS_REG(0x805) op_mod(0x1) failed, status bad system state(0x4), syndrome (0x685f19), err(-5)

Fixes: 678eb448 ("net/mlx5: SD, Implement basic query and instantiation")
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx5/core/lib/sd.c

@@ -100,10 +100,6 @@ static bool ft_create_alias_supported(struct mlx5_core_dev *dev)
 
 static bool mlx5_sd_is_supported(struct mlx5_core_dev *dev, u8 host_buses)
 {
-	/* Feature is currently implemented for PFs only */
-	if (!mlx5_core_is_pf(dev))
-		return false;
-
 	/* Honor the SW implementation limit */
 	if (host_buses > MLX5_SD_MAX_GROUP_SZ)
 		return false;
@@ -162,6 +158,14 @@ static int sd_init(struct mlx5_core_dev *dev)
 	bool sdm;
 	int err;
 
+	/* Feature is currently implemented for PFs only */
+	if (!mlx5_core_is_pf(dev))
+		return 0;
+
+	/* Block on embedded CPU PFs */
+	if (mlx5_core_is_ecpf(dev))
+		return 0;
+
 	if (!MLX5_CAP_MCAM_REG(dev, mpir))
 		return 0;