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 <[e-mail]>
Reviewed-by: Benjamin Herrenschmidt <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/ast/ast_main.c

···
 
 
 	/* 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);
···
 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);

drivers/gpu/drm/ast/ast_mode.c

···
 		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

···
 {
 	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);
 }