diff --git a/src/northbridge/intel/x4x/Kconfig b/src/northbridge/intel/x4x/Kconfig
index bdef6f2..32e85d3 100644
--- a/src/northbridge/intel/x4x/Kconfig
+++ b/src/northbridge/intel/x4x/Kconfig
@@ -25,6 +25,10 @@
 config MMCONF_BASE_ADDRESS
 	default 0xe0000000
 
+config MMCONF_BUS_NUMBER
+	int
+	default 256
+
 config SMM_RESERVED_SIZE
 	hex
 	default 0x100000
diff --git a/src/northbridge/intel/x4x/acpi.c b/src/northbridge/intel/x4x/acpi.c
index 4088e75..8f94b34 100644
--- a/src/northbridge/intel/x4x/acpi.c
+++ b/src/northbridge/intel/x4x/acpi.c
@@ -1,6 +1,5 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
-#include <types.h>
 #include <console/console.h>
 #include <acpi/acpi.h>
 #include <acpi/acpigen.h>
@@ -9,13 +8,8 @@
 
 unsigned long acpi_fill_mcfg(unsigned long current)
 {
-	u32 pciexbar, length;
-
-	if (!decode_pcie_bar(&pciexbar, &length))
-		return current;
-
-	current += acpi_create_mcfg_mmconfig((acpi_mcfg_mmconfig_t *) current,
-			pciexbar, 0x0, 0x0, (length >> 20) - 1);
+	current += acpi_create_mcfg_mmconfig((acpi_mcfg_mmconfig_t *)current,
+			CONFIG_MMCONF_BASE_ADDRESS, 0, 0, CONFIG_MMCONF_BUS_NUMBER - 1);
 
 	return current;
 }
diff --git a/src/northbridge/intel/x4x/acpi/x4x.asl b/src/northbridge/intel/x4x/acpi/x4x.asl
index b013da7..33cb7ad 100644
--- a/src/northbridge/intel/x4x/acpi/x4x.asl
+++ b/src/northbridge/intel/x4x/acpi/x4x.asl
@@ -15,7 +15,7 @@
 		Memory32Fixed(ReadWrite, DEFAULT_MCHBAR,   0x00004000)
 		Memory32Fixed(ReadWrite, DEFAULT_DMIBAR,   0x00001000)
 		Memory32Fixed(ReadWrite, DEFAULT_EPBAR,    0x00001000)
-		Memory32Fixed(ReadWrite, CONFIG_MMCONF_BASE_ADDRESS, 0x04000000)
+		Memory32Fixed(ReadWrite, CONFIG_MMCONF_BASE_ADDRESS, CONFIG_MMCONF_LENGTH)
 		Memory32Fixed(ReadWrite, 0xfed20000, 0x00020000) // Misc ICH
 		Memory32Fixed(ReadWrite, 0xfed40000, 0x00005000) // Misc ICH
 		Memory32Fixed(ReadWrite, 0xfed45000, 0x0004b000) // Misc ICH
diff --git a/src/northbridge/intel/x4x/bootblock.c b/src/northbridge/intel/x4x/bootblock.c
index 1192fdb..f15d181 100644
--- a/src/northbridge/intel/x4x/bootblock.c
+++ b/src/northbridge/intel/x4x/bootblock.c
@@ -2,15 +2,27 @@
 
 #include <arch/bootblock.h>
 #include <arch/mmio.h>
+#include <assert.h>
 #include <device/pci_ops.h>
+#include <types.h>
 
 #include "x4x.h"
 
+static uint32_t encode_pciexbar_length(void)
+{
+	switch (CONFIG_MMCONF_BUS_NUMBER) {
+		case 256: return 0 << 1;
+		case 128: return 1 << 1;
+		case  64: return 2 << 1;
+		default:  return dead_code_t(uint32_t);
+	}
+}
+
 void bootblock_early_northbridge_init(void)
 {
 	/* Disable LaGrande Technology (LT) */
 	read32((void *)TPM_BASE_ADDRESS);
 
-	const uint32_t reg32 = CONFIG_MMCONF_BASE_ADDRESS | 16 | 1;
+	const uint32_t reg32 = CONFIG_MMCONF_BASE_ADDRESS | encode_pciexbar_length() | 1;
 	pci_io_write_config32(HOST_BRIDGE, D0F0_PCIEXBAR_LO, reg32);
 }
diff --git a/src/northbridge/intel/x4x/memmap.c b/src/northbridge/intel/x4x/memmap.c
index aa737f3..5114e0b 100644
--- a/src/northbridge/intel/x4x/memmap.c
+++ b/src/northbridge/intel/x4x/memmap.c
@@ -57,42 +57,6 @@
 	}
 }
 
-int decode_pcie_bar(u32 *const base, u32 *const len)
-{
-	*base = 0;
-	*len = 0;
-
-	const struct {
-		u16 num_buses;
-		u32 addr_mask;
-	} busmask[] = {
-		{256, 0xf0000000},
-		{128, 0xf8000000},
-		{64,  0xfc000000},
-		{0,   0},
-	};
-
-	const u32 pciexbar_reg = pci_read_config32(HOST_BRIDGE, D0F0_PCIEXBAR_LO);
-
-	if (!(pciexbar_reg & 1)) {
-		printk(BIOS_WARNING, "WARNING: MMCONF not set\n");
-		return 0;
-	}
-
-	const u32 index = (pciexbar_reg >> 1) & 3;
-	const u32 pciexbar = pciexbar_reg & busmask[index].addr_mask;
-	const int max_buses = busmask[index].num_buses;
-
-	if (!pciexbar) {
-		printk(BIOS_WARNING, "WARNING: pciexbar invalid\n");
-		return 0;
-	}
-
-	*base = pciexbar;
-	*len = max_buses << 20;
-	return 1;
-}
-
 static size_t northbridge_get_tseg_size(void)
 {
 	const u8 esmramc = pci_read_config8(HOST_BRIDGE, D0F0_ESMRAMC);
diff --git a/src/northbridge/intel/x4x/northbridge.c b/src/northbridge/intel/x4x/northbridge.c
index 5e46270..de60338 100644
--- a/src/northbridge/intel/x4x/northbridge.c
+++ b/src/northbridge/intel/x4x/northbridge.c
@@ -20,7 +20,6 @@
 	u8 index;
 	u64 tom, touud;
 	u32 tomk, tolud, delta_cbmem;
-	u32 pcie_config_base, pcie_config_size;
 	u32 uma_sizek = 0;
 
 	const u32 top32memk = 4 * (GiB / KiB);
@@ -111,12 +110,7 @@
 				top32memk - (DEFAULT_HECIBAR >> 10),
 				IORESOURCE_RESERVE);
 
-	if (decode_pcie_bar(&pcie_config_base, &pcie_config_size)) {
-		printk(BIOS_DEBUG, "Adding PCIe config bar base=0x%08x "
-		       "size=0x%x\n", pcie_config_base, pcie_config_size);
-		fixed_mem_resource(dev, index++, pcie_config_base >> 10,
-			pcie_config_size >> 10, IORESOURCE_RESERVE);
-	}
+	mmconf_resource(dev, index++);
 }
 
 static void mch_domain_set_resources(struct device *dev)
diff --git a/src/northbridge/intel/x4x/x4x.h b/src/northbridge/intel/x4x/x4x.h
index ea34fe0..33f7a4c 100644
--- a/src/northbridge/intel/x4x/x4x.h
+++ b/src/northbridge/intel/x4x/x4x.h
@@ -172,7 +172,6 @@
 u32 decode_igd_memory_size(u32 gms);
 u32 decode_igd_gtt_size(u32 gsm);
 u32 decode_tseg_size(const u32 esmramc);
-int decode_pcie_bar(u32 *const base, u32 *const len);
 
 #include <device/device.h>
 struct acpi_rsdp;