mips_malta: correct reading MIPS revision at 0x1fc00010

Rather than modifying the BIOS code at its original location, copy it
for the 0x1fc00000 region & modify the copy. This means the original
ROM code is correctly readable at 0x1e000010 whilst the MIPS revision
is readable at 0x1fc00010.

Additionally the code previously operated on target memory which would
later be overwritten by the BIOS image upon CPU reset if the -bios
argument was used to specify the BIOS image. This led to the written
MIPS revision being lost. Copying using rom_copy when -bios is used
fixes this issue.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

hw/mips/mips_malta.c

@@ -793,7 +793,7 @@ void mips_malta_init(QEMUMachineInitArgs *args)
     pflash_t *fl;
     MemoryRegion *system_memory = get_system_memory();
     MemoryRegion *ram = g_new(MemoryRegion, 1);
-    MemoryRegion *bios, *bios_alias = g_new(MemoryRegion, 1);
+    MemoryRegion *bios, *bios_copy = g_new(MemoryRegion, 1);
     target_long bios_size = FLASH_SIZE;
     int64_t kernel_entry;
     PCIBus *pci_bus;
@@ -933,14 +933,23 @@ void mips_malta_init(QEMUMachineInitArgs *args)
 #endif
     }
 
-    /* Map the BIOS at a 2nd physical location, as on the real board. */
-    memory_region_init_alias(bios_alias, NULL, "bios.1fc", bios, 0, BIOS_SIZE);
-    memory_region_add_subregion(system_memory, RESET_ADDRESS, bios_alias);
+    /*
+     * Map the BIOS at a 2nd physical location, as on the real board.
+     * Copy it so that we can patch in the MIPS revision, which cannot be
+     * handled by an overlapping region as the resulting ROM code subpage
+     * regions are not executable.
+     */
+    memory_region_init_ram(bios_copy, NULL, "bios.1fc", BIOS_SIZE);
+    if (!rom_copy(memory_region_get_ram_ptr(bios_copy),
+                  FLASH_ADDRESS, bios_size)) {
+        memcpy(memory_region_get_ram_ptr(bios_copy),
+               memory_region_get_ram_ptr(bios), bios_size);
+    }
+    memory_region_set_readonly(bios_copy, true);
+    memory_region_add_subregion(system_memory, RESET_ADDRESS, bios_copy);
 
-    /* Board ID = 0x420 (Malta Board with CoreLV)
-       XXX: theoretically 0x1e000010 should map to flash and 0x1fc00010 should
-       map to the board ID. */
-    stl_p(memory_region_get_ram_ptr(bios) + 0x10, 0x00000420);
+    /* Board ID = 0x420 (Malta Board with CoreLV) */
+    stl_p(memory_region_get_ram_ptr(bios_copy) + 0x10, 0x00000420);
 
     /* Init internal devices */
     cpu_mips_irq_init_cpu(env);