q800: add machine id register

MacOS reads this address to identify the hardware.

This is a basic implementation returning the ID of Quadra 800.

Details:

  http://mess.redump.net/mess/driver_info/mac_technical_notes

"There are 3 ID schemes [...]
 The third and most scalable is a machine ID register at 0x5ffffffc.
 The top word must be 0xa55a to be valid. Then bits 15-11 are 0 for
 consumer Macs, 1 for portables, 2 for high-end 68k, and 3 for high-end
 PowerPC. Bit 10 is 1 if additional ID bits appear elsewhere (e.g. in VIA1).
 The rest of the bits are a per-model identifier.

 Model                          Lower 16 bits of ID
...
 Quadra/Centris 610/650/800     0x2BAD"

Co-developed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20231004083806.757242-4-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

hw/m68k/q800.c

@@ -91,6 +91,9 @@
 #define Q800_NUBUS_SLOTS_AVAILABLE    (BIT(0x9) | BIT(0xc) | BIT(0xd) | \
                                        BIT(0xe))
 
+/* Quadra 800 machine ID */
+#define Q800_MACHINE_ID    0xa55a2bad
+
 
 static void main_cpu_reset(void *opaque)
 {
@@ -192,6 +195,27 @@ static const MemoryRegionOps macio_alias_ops = {
     },
 };
 
+static uint64_t machine_id_read(void *opaque, hwaddr addr, unsigned size)
+{
+    return Q800_MACHINE_ID;
+}
+
+static void machine_id_write(void *opaque, hwaddr addr, uint64_t val,
+                             unsigned size)
+{
+    return;
+}
+
+static const MemoryRegionOps machine_id_ops = {
+    .read = machine_id_read,
+    .write = machine_id_write,
+    .endianness = DEVICE_BIG_ENDIAN,
+    .valid = {
+        .min_access_size = 4,
+        .max_access_size = 4,
+    },
+};
+
 static void q800_machine_init(MachineState *machine)
 {
     Q800MachineState *m = Q800_MACHINE(machine);
@@ -253,6 +277,11 @@ static void q800_machine_init(MachineState *machine)
     memory_region_add_subregion(get_system_memory(), IO_BASE + IO_SLICE,
                                 &m->macio_alias);
 
+    memory_region_init_io(&m->machine_id, NULL, &machine_id_ops, NULL,
+                          "Machine ID", 4);
+    memory_region_add_subregion(get_system_memory(), 0x5ffffffc,
+                                &m->machine_id);
+
     /* IRQ Glue */
     object_initialize_child(OBJECT(machine), "glue", &m->glue, TYPE_GLUE);
     object_property_set_link(OBJECT(&m->glue), "cpu", OBJECT(&m->cpu),

include/hw/m68k/q800.h

@@ -60,6 +60,7 @@ struct Q800MachineState {
     DJMEMCState djmemc;
     MemoryRegion macio;
     MemoryRegion macio_alias;
+    MemoryRegion machine_id;
 };
 
 #define TYPE_Q800_MACHINE MACHINE_TYPE_NAME("q800")