ati-vga: Add dummy MEM_SDRAM_MODE_REG

Radeon chips have an SDRAM mode reg that is accessed by some drivers.
We don't emulate the memory controller but provide some default value
to prevent drivers getting unexpected 0.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Message-id: cc1324b9ef06beb8ae233ddc77dedd8bab9b8624.1592737958.git.balaton@eik.bme.hu
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/display/ati.c

@@ -361,6 +361,11 @@ static uint64_t ati_mm_read(void *opaque, hwaddr addr, unsigned int size)
     case MC_STATUS:
         val = 5;
         break;
+    case MEM_SDRAM_MODE_REG:
+        if (s->dev_id != PCI_DEVICE_ID_ATI_RAGE128_PF) {
+            val = BIT(28) | BIT(20);
+        }
+        break;
     case RBBM_STATUS:
     case GUI_STAT:
         val = 64; /* free CMDFIFO entries */

hw/display/ati_dbg.c

@@ -42,6 +42,7 @@ static struct ati_regdesc ati_reg_names[] = {
     {"MC_FB_LOCATION", 0x0148},
     {"MC_AGP_LOCATION", 0x014C},
     {"MC_STATUS", 0x0150},
+    {"MEM_SDRAM_MODE_REG", 0x0158},
     {"MEM_POWER_MISC", 0x015c},
     {"AGP_BASE", 0x0170},
     {"AGP_CNTL", 0x0174},

hw/display/ati_regs.h

@@ -60,6 +60,7 @@
 #define MC_FB_LOCATION                          0x0148
 #define MC_AGP_LOCATION                         0x014C
 #define MC_STATUS                               0x0150
+#define MEM_SDRAM_MODE_REG                      0x0158
 #define MEM_POWER_MISC                          0x015c
 #define AGP_BASE                                0x0170
 #define AGP_CNTL                                0x0174