diff --git a/hw/mips/gt64xxx_pci.c b/hw/mips/gt64xxx_pci.c
index 65416c7b27..81232514c5 100644
--- a/hw/mips/gt64xxx_pci.c
+++ b/hw/mips/gt64xxx_pci.c
@@ -298,6 +298,50 @@ static void gt64120_isd_mapping(GT64120State *s)
     memory_region_transaction_commit();
 }
 
+static void gt64120_update_pci_cfgdata_mapping(GT64120State *s)
+{
+    /* Indexed on MByteSwap bit, see Table 158: PCI_0 Command, Offset: 0xc00 */
+    static const MemoryRegionOps *pci_host_conf_ops[] = {
+        &pci_host_conf_be_ops, &pci_host_conf_le_ops
+    };
+    static const MemoryRegionOps *pci_host_data_ops[] = {
+        &pci_host_data_be_ops, &pci_host_data_le_ops
+    };
+    PCIHostState *phb = PCI_HOST_BRIDGE(s);
+
+    memory_region_transaction_begin();
+
+    /*
+     * The setting of the MByteSwap bit and MWordSwap bit in the PCI Internal
+     * Command Register determines how data transactions from the CPU to/from
+     * PCI are handled along with the setting of the Endianess bit in the CPU
+     * Configuration Register. See:
+     * - Table 16: 32-bit PCI Transaction Endianess
+     * - Table 158: PCI_0 Command, Offset: 0xc00
+     */
+    if (memory_region_is_mapped(&phb->conf_mem)) {
+        memory_region_del_subregion(&s->ISD_mem, &phb->conf_mem);
+        object_unparent(OBJECT(&phb->conf_mem));
+    }
+    memory_region_init_io(&phb->conf_mem, OBJECT(phb),
+                          pci_host_conf_ops[s->regs[GT_PCI0_CMD] & 1],
+                          s, "pci-conf-idx", 4);
+    memory_region_add_subregion_overlap(&s->ISD_mem, GT_PCI0_CFGADDR << 2,
+                                        &phb->conf_mem, 1);
+
+    if (memory_region_is_mapped(&phb->data_mem)) {
+        memory_region_del_subregion(&s->ISD_mem, &phb->data_mem);
+        object_unparent(OBJECT(&phb->data_mem));
+    }
+    memory_region_init_io(&phb->data_mem, OBJECT(phb),
+                          pci_host_data_ops[s->regs[GT_PCI0_CMD] & 1],
+                          s, "pci-conf-data", 4);
+    memory_region_add_subregion_overlap(&s->ISD_mem, GT_PCI0_CFGDATA << 2,
+                                        &phb->data_mem, 1);
+
+    memory_region_transaction_commit();
+}
+
 static void gt64120_pci_mapping(GT64120State *s)
 {
     memory_region_transaction_begin();
@@ -389,7 +433,6 @@ static void gt64120_writel(void *opaque, hwaddr addr,
                            uint64_t val, unsigned size)
 {
     GT64120State *s = opaque;
-    PCIHostState *phb = PCI_HOST_BRIDGE(s);
     uint32_t saddr = addr >> 2;
 
     trace_gt64120_write(addr, val);
@@ -592,6 +635,7 @@ static void gt64120_writel(void *opaque, hwaddr addr,
     case GT_PCI0_CMD:
     case GT_PCI1_CMD:
         s->regs[saddr] = val & 0x0401fc0f;
+        gt64120_update_pci_cfgdata_mapping(s);
         break;
     case GT_PCI0_TOR:
     case GT_PCI0_BS_SCS10:
@@ -632,15 +676,9 @@ static void gt64120_writel(void *opaque, hwaddr addr,
                       saddr << 2, size, size << 1, val);
         break;
     case GT_PCI0_CFGADDR:
-        phb->config_reg = val & 0x80fffffc;
-        break;
     case GT_PCI0_CFGDATA:
-        if (!(s->regs[GT_PCI0_CMD] & 1) && (phb->config_reg & 0x00fff800)) {
-            val = bswap32(val);
-        }
-        if (phb->config_reg & (1u << 31)) {
-            pci_data_write(phb->bus, phb->config_reg, val, 4);
-        }
+        /* Mapped via in gt64120_pci_mapping() */
+        g_assert_not_reached();
         break;
 
     /* Interrupts */
@@ -698,7 +736,6 @@ static uint64_t gt64120_readl(void *opaque,
                               hwaddr addr, unsigned size)
 {
     GT64120State *s = opaque;
-    PCIHostState *phb = PCI_HOST_BRIDGE(s);
     uint32_t val;
     uint32_t saddr = addr >> 2;
 
@@ -883,17 +920,9 @@ static uint64_t gt64120_readl(void *opaque,
 
     /* PCI Internal */
     case GT_PCI0_CFGADDR:
-        val = phb->config_reg;
-        break;
     case GT_PCI0_CFGDATA:
-        if (!(phb->config_reg & (1 << 31))) {
-            val = 0xffffffff;
-        } else {
-            val = pci_data_read(phb->bus, phb->config_reg, 4);
-        }
-        if (!(s->regs[GT_PCI0_CMD] & 1) && (phb->config_reg & 0x00fff800)) {
-            val = bswap32(val);
-        }
+        /* Mapped via in gt64120_pci_mapping() */
+        g_assert_not_reached();
         break;
 
     case GT_PCI0_CMD:
@@ -1153,6 +1182,7 @@ static void gt64120_reset(DeviceState *dev)
 
     gt64120_isd_mapping(s);
     gt64120_pci_mapping(s);
+    gt64120_update_pci_cfgdata_mapping(s);
 }
 
 static void gt64120_realize(DeviceState *dev, Error **errp)
