diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
index 372abff1c8673..a823dcbf73c4b 100644
--- a/drivers/gpu/drm/ast/ast_mode.c
+++ b/drivers/gpu/drm/ast/ast_mode.c
@@ -107,59 +107,6 @@ static void ast_crtc_set_gamma(struct ast_device *ast,
 	}
 }
 
-static bool ast_get_vbios_mode_info(struct ast_device *ast,
-				    const struct drm_format_info *format,
-				    const struct drm_display_mode *mode,
-				    struct drm_display_mode *adjusted_mode,
-				    struct ast_vbios_mode_info *vbios_mode)
-{
-	u32 hborder, vborder;
-
-	switch (format->cpp[0] * 8) {
-	case 8:
-		vbios_mode->std_table = &vbios_stdtable[VGAModeIndex];
-		break;
-	case 16:
-		vbios_mode->std_table = &vbios_stdtable[HiCModeIndex];
-		break;
-	case 24:
-	case 32:
-		vbios_mode->std_table = &vbios_stdtable[TrueCModeIndex];
-		break;
-	default:
-		return false;
-	}
-
-	vbios_mode->enh_table = ast_vbios_find_mode(ast, mode);
-	if (!vbios_mode->enh_table)
-		return false;
-
-	hborder = (vbios_mode->enh_table->flags & HBorder) ? 8 : 0;
-	vborder = (vbios_mode->enh_table->flags & VBorder) ? 8 : 0;
-
-	adjusted_mode->crtc_hdisplay = vbios_mode->enh_table->hde;
-	adjusted_mode->crtc_htotal = vbios_mode->enh_table->ht;
-	adjusted_mode->crtc_hblank_start = vbios_mode->enh_table->hde + hborder;
-	adjusted_mode->crtc_hblank_end = vbios_mode->enh_table->ht - hborder;
-	adjusted_mode->crtc_hsync_start = vbios_mode->enh_table->hde + hborder +
-		vbios_mode->enh_table->hfp;
-	adjusted_mode->crtc_hsync_end = (vbios_mode->enh_table->hde + hborder +
-					 vbios_mode->enh_table->hfp +
-					 vbios_mode->enh_table->hsync);
-
-	adjusted_mode->crtc_vdisplay = vbios_mode->enh_table->vde;
-	adjusted_mode->crtc_vtotal = vbios_mode->enh_table->vt;
-	adjusted_mode->crtc_vblank_start = vbios_mode->enh_table->vde + vborder;
-	adjusted_mode->crtc_vblank_end = vbios_mode->enh_table->vt - vborder;
-	adjusted_mode->crtc_vsync_start = vbios_mode->enh_table->vde + vborder +
-		vbios_mode->enh_table->vfp;
-	adjusted_mode->crtc_vsync_end = (vbios_mode->enh_table->vde + vborder +
-					 vbios_mode->enh_table->vfp +
-					 vbios_mode->enh_table->vsync);
-
-	return true;
-}
-
 static void ast_set_vbios_color_reg(struct ast_device *ast,
 				    const struct drm_format_info *format,
 				    const struct ast_vbios_mode_info *vbios_mode)
@@ -990,13 +937,17 @@ static int ast_crtc_helper_atomic_check(struct drm_crtc *crtc,
 					struct drm_atomic_state *state)
 {
 	struct drm_crtc_state *crtc_state = drm_atomic_get_new_crtc_state(state, crtc);
+	struct drm_display_mode *adjusted_mode = &crtc_state->adjusted_mode;
 	struct drm_crtc_state *old_crtc_state = drm_atomic_get_old_crtc_state(state, crtc);
 	struct ast_crtc_state *old_ast_crtc_state = to_ast_crtc_state(old_crtc_state);
 	struct drm_device *dev = crtc->dev;
 	struct ast_device *ast = to_ast_device(dev);
 	struct ast_crtc_state *ast_state;
 	const struct drm_format_info *format;
-	bool succ;
+	struct ast_vbios_mode_info *vbios_mode;
+	const struct ast_vbios_enhtable *vmode;
+	unsigned int hborder = 0;
+	unsigned int vborder = 0;
 	int ret;
 
 	if (!crtc_state->enable)
@@ -1028,11 +979,56 @@ static int ast_crtc_helper_atomic_check(struct drm_crtc *crtc,
 		}
 	}
 
-	succ = ast_get_vbios_mode_info(ast, format, &crtc_state->mode,
-				       &crtc_state->adjusted_mode,
-				       &ast_state->vbios_mode_info);
-	if (!succ)
+	vbios_mode = &ast_state->vbios_mode_info;
+
+	/*
+	 * Set register tables.
+	 *
+	 * TODO: These tables mix all kinds of fields and should
+	 *       probably be resolved into various helper functions.
+	 */
+	switch (format->format) {
+	case DRM_FORMAT_C8:
+		vbios_mode->std_table = &vbios_stdtable[VGAModeIndex];
+		break;
+	case DRM_FORMAT_RGB565:
+		vbios_mode->std_table = &vbios_stdtable[HiCModeIndex];
+		break;
+	case DRM_FORMAT_RGB888:
+	case DRM_FORMAT_XRGB8888:
+		vbios_mode->std_table = &vbios_stdtable[TrueCModeIndex];
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/*
+	 * Find the VBIOS mode and adjust the DRM display mode accordingly.
+	 */
+
+	vmode = ast_vbios_find_mode(ast, &crtc_state->mode);
+	if (!vmode)
 		return -EINVAL;
+	ast_state->vbios_mode_info.enh_table = vmode;
+
+	if (vmode->flags & HBorder)
+		hborder = 8;
+	if (vmode->flags & VBorder)
+		vborder = 8;
+
+	adjusted_mode->crtc_hdisplay = vmode->hde;
+	adjusted_mode->crtc_hblank_start = vmode->hde + hborder;
+	adjusted_mode->crtc_hblank_end = vmode->ht - hborder;
+	adjusted_mode->crtc_hsync_start = vmode->hde + hborder + vmode->hfp;
+	adjusted_mode->crtc_hsync_end = vmode->hde + hborder + vmode->hfp + vmode->hsync;
+	adjusted_mode->crtc_htotal = vmode->ht;
+
+	adjusted_mode->crtc_vdisplay = vmode->vde;
+	adjusted_mode->crtc_vblank_start = vmode->vde + vborder;
+	adjusted_mode->crtc_vblank_end = vmode->vt - vborder;
+	adjusted_mode->crtc_vsync_start = vmode->vde + vborder + vmode->vfp;
+	adjusted_mode->crtc_vsync_end = vmode->vde + vborder + vmode->vfp + vmode->vsync;
+	adjusted_mode->crtc_vtotal = vmode->vt;
 
 	return 0;
 }
