[PULL 3/4] q800: implement mac rom reset function for BIOS-less mode

[Laurent Vivier <laurent@vivier.eu>]

From: "Jason A. Donenfeld" <Jason@zx2c4.com>

On Linux, calling `reboot(RB_AUTOBOOT);` will result in
arch/m68k/mac/misc.c's mac_reset function being called. That in turn
looks at the rombase (or uses 0x40800000 is there's no rombase), adds
0xa, and jumps to that address. At the moment, there's nothing there, so
the kernel just crashes when trying to reboot. So, this commit adds a
very simple implementation at that location, which just writes to via2
to power down. We also correct the value of ROMBASE while we're at it.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20200102120150.281082-1-Jason@zx2c4.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
---
 hw/m68k/q800.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/hw/m68k/q800.c b/hw/m68k/q800.c
index 0c445c74bf..0e5a08f993 100644
--- a/hw/m68k/q800.c
+++ b/hw/m68k/q800.c
@@ -47,7 +47,7 @@
 #include "sysemu/runstate.h"
 #include "sysemu/reset.h"
 
-#define MACROM_ADDR     0x40000000
+#define MACROM_ADDR     0x40800000
 #define MACROM_SIZE     0x00100000
 
 #define MACROM_FILENAME "MacROM.bin"
@@ -128,6 +128,27 @@ static void main_cpu_reset(void *opaque)
     cpu->env.pc = ldl_phys(cs->as, 4);
 }
 
+static uint8_t fake_mac_rom[] = {
+    0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+
+    /* offset: 0xa - mac_reset */
+
+    /* via2[vDirB] |= VIA2B_vPower */
+    0x20, 0x7C, 0x50, 0xF0, 0x24, 0x00, /* moveal VIA2_BASE+vDirB,%a0 */
+    0x10, 0x10,                         /* moveb %a0@,%d0 */
+    0x00, 0x00, 0x00, 0x04,             /* orib #4,%d0 */
+    0x10, 0x80,                         /* moveb %d0,%a0@ */
+
+    /* via2[vBufB] &= ~VIA2B_vPower */
+    0x20, 0x7C, 0x50, 0xF0, 0x20, 0x00, /* moveal VIA2_BASE+vBufB,%a0 */
+    0x10, 0x10,                         /* moveb %a0@,%d0 */
+    0x02, 0x00, 0xFF, 0xFB,             /* andib #-5,%d0 */
+    0x10, 0x80,                         /* moveb %d0,%a0@ */
+
+    /* while (true) ; */
+    0x60, 0xFE                          /* bras [self] */
+};
+
 static void q800_init(MachineState *machine)
 {
     M68kCPU *cpu = NULL;
@@ -346,6 +367,12 @@ static void q800_init(MachineState *machine)
                   (graphic_width * graphic_depth + 7) / 8);
         BOOTINFO1(cs->as, parameters_base, BI_MAC_SCCBASE, SCC_BASE);
 
+        rom = g_malloc(sizeof(*rom));
+        memory_region_init_ram_ptr(rom, NULL, "m68k_fake_mac.rom",
+                                   sizeof(fake_mac_rom), fake_mac_rom);
+        memory_region_set_readonly(rom, true);
+        memory_region_add_subregion(get_system_memory(), MACROM_ADDR, rom);
+
         if (kernel_cmdline) {
             BOOTINFOSTR(cs->as, parameters_base, BI_COMMAND_LINE,
                         kernel_cmdline);
-- 
2.24.1