drm/nv50: hopefully handle the DDR2/DDR3 memtype detection somewhat better

M version 2 appears to have a table with some form of memory type info
available.

NVIDIA appear to ignore the table information except for this DDR2/DDR3
case (which has the same value in 0x100714).  My guess is this is due to
some of the supported memory types not being represented in the table.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_mem.c

@@ -683,6 +683,29 @@ nouveau_mem_timing_fini(struct drm_device *dev)
 	}
 }
 
+int
+nouveau_mem_vbios_type(struct drm_device *dev)
+{
+	struct bit_entry M;
+	u8 ramcfg = (nv_rd32(dev, 0x101000) & 0x0000003c) >> 2;
+	if (!bit_table(dev, 'M', &M) || M.version != 2 || M.length < 5) {
+		u8 *table = ROMPTR(dev, M.data[3]);
+		if (table && table[0] == 0x10 && ramcfg < table[3]) {
+			u8 *entry = table + table[1] + (ramcfg * table[2]);
+			switch (entry[0] & 0x0f) {
+			case 0: return NV_MEM_TYPE_DDR2;
+			case 1: return NV_MEM_TYPE_DDR3;
+			case 2: return NV_MEM_TYPE_GDDR3;
+			case 3: return NV_MEM_TYPE_GDDR5;
+			default:
+				break;
+			}
+
+		}
+	}
+	return NV_MEM_TYPE_UNKNOWN;
+}
+
 static int
 nouveau_vram_manager_init(struct ttm_mem_type_manager *man, unsigned long psize)
 {