[PATCH] drm/ast: Fix incorrect memory size detection with analog VGA

[Timothy Pearson]

On mainboards with analog VGA output the memory size is incorrectly
detected due to an invalid register probe.  This leads to a corrupted
and unusable framebuffer on the analog VGA output.

Do not probe the DP501-related VGA scratch register if the DP501
device was not detected.

Tested-on: ASUS KGPE-D16 (AST2050) w/ 8MB VRAM.

Signed-off-by: Timothy Pearson <tpearson at raptorengineering.com>
---
 drivers/gpu/drm/ast/ast_main.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/ast/ast_main.c b/drivers/gpu/drm/ast/ast_main.c
index 7bc3aa6..090b571 100644
--- a/drivers/gpu/drm/ast/ast_main.c
+++ b/drivers/gpu/drm/ast/ast_main.c
@@ -372,17 +372,19 @@ static u32 ast_get_vram_info(struct drm_device *dev)
        case 3: vram_size = AST_VIDMEM_SIZE_64M; break;
        }

-       jreg = ast_get_index_reg_mask(ast, AST_IO_CRTC_PORT, 0x99, 0xff);
-       switch (jreg & 0x03) {
-       case 1:
-               vram_size -= 0x100000;
-               break;
-       case 2:
-               vram_size -= 0x200000;
-               break;
-       case 3:
-               vram_size -= 0x400000;
-               break;
+       if (ast->tx_chip_type == AST_TX_DP501) {
+               jreg = ast_get_index_reg_mask(ast, AST_IO_CRTC_PORT, 0x99, 
0xff);
+               switch (jreg & 0x03) {
+               case 1:
+                       vram_size -= 0x100000;
+                       break;
+               case 2:
+                       vram_size -= 0x200000;
+                       break;
+               case 3:
+                       vram_size -= 0x400000;
+                       break;
+               }
        }

        return vram_size;
-- 
2.8.1