drm/ast: Fixed reboot test may cause system hanged

There is another thread still access standard VGA I/O while loading drm driver.
Disable standard VGA I/O decode to avoid this issue.
Signed-off-by: Y.C. Chen <yc_chen@aspeedtech.com>
Reviewed-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1523410059-18415-1-git-send-email-yc_chen@aspeedtech.com

drivers/gpu/drm/ast/ast_main.c

@@ -131,8 +131,8 @@ static int ast_detect_chip(struct drm_device *dev, bool *need_post)
 
 
 	/* Enable extended register access */
-	ast_enable_mmio(dev);
 	ast_open_key(ast);
+	ast_enable_mmio(dev);
 
 	/* Find out whether P2A works or whether to use device-tree */
 	ast_detect_config_mode(dev, &scu_rev);
@@ -576,6 +576,9 @@ void ast_driver_unload(struct drm_device *dev)
 {
 	struct ast_private *ast = dev->dev_private;
 
+	/* enable standard VGA decode */
+	ast_set_index_reg(ast, AST_IO_CRTC_PORT, 0xa1, 0x04);
+
 	ast_release_firmware(dev);
 	kfree(ast->dp501_fw_addr);
 	ast_mode_fini(dev);

drivers/gpu/drm/ast/ast_mode.c

@@ -604,7 +604,7 @@ static int ast_crtc_mode_set(struct drm_crtc *crtc,
 		return -EINVAL;
 	ast_open_key(ast);
 
-	ast_set_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xa1, 0xff, 0x04);
+	ast_set_index_reg(ast, AST_IO_CRTC_PORT, 0xa1, 0x06);
 
 	ast_set_std_reg(crtc, adjusted_mode, &vbios_mode);
 	ast_set_crtc_reg(crtc, adjusted_mode, &vbios_mode);

drivers/gpu/drm/ast/ast_post.c

@@ -46,7 +46,7 @@ void ast_enable_mmio(struct drm_device *dev)
 {
 	struct ast_private *ast = dev->dev_private;
 
-	ast_set_index_reg_mask(ast, AST_IO_CRTC_PORT, 0xa1, 0xff, 0x04);
+	ast_set_index_reg(ast, AST_IO_CRTC_PORT, 0xa1, 0x06);
 }