drm: fb-helper: Reject all pixel format changing requests

drm fbdev emulation doesn't support changing the pixel format at all,
so reject all pixel format changing requests.

Cc: stable@vger.kernel.org
Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20181003164538.5534-1-Eugeniy.Paltsev@synopsys.com

drivers/gpu/drm/drm_fb_helper.c

@@ -1580,6 +1580,25 @@ int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd,
 }
 EXPORT_SYMBOL(drm_fb_helper_ioctl);
 
+static bool drm_fb_pixel_format_equal(const struct fb_var_screeninfo *var_1,
+				      const struct fb_var_screeninfo *var_2)
+{
+	return var_1->bits_per_pixel == var_2->bits_per_pixel &&
+	       var_1->grayscale == var_2->grayscale &&
+	       var_1->red.offset == var_2->red.offset &&
+	       var_1->red.length == var_2->red.length &&
+	       var_1->red.msb_right == var_2->red.msb_right &&
+	       var_1->green.offset == var_2->green.offset &&
+	       var_1->green.length == var_2->green.length &&
+	       var_1->green.msb_right == var_2->green.msb_right &&
+	       var_1->blue.offset == var_2->blue.offset &&
+	       var_1->blue.length == var_2->blue.length &&
+	       var_1->blue.msb_right == var_2->blue.msb_right &&
+	       var_1->transp.offset == var_2->transp.offset &&
+	       var_1->transp.length == var_2->transp.length &&
+	       var_1->transp.msb_right == var_2->transp.msb_right;
+}
+
 /**
  * drm_fb_helper_check_var - implementation for &fb_ops.fb_check_var
  * @var: screeninfo to check
@@ -1590,7 +1609,6 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
 {
 	struct drm_fb_helper *fb_helper = info->par;
 	struct drm_framebuffer *fb = fb_helper->fb;
-	int depth;
 
 	if (var->pixclock != 0 || in_dbg_master())
 		return -EINVAL;
@@ -1610,72 +1628,15 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
 		return -EINVAL;
 	}
 
-	switch (var->bits_per_pixel) {
-	case 16:
-		depth = (var->green.length == 6) ? 16 : 15;
-		break;
-	case 32:
-		depth = (var->transp.length > 0) ? 32 : 24;
-		break;
-	default:
-		depth = var->bits_per_pixel;
-		break;
-	}
-
-	switch (depth) {
-	case 8:
-		var->red.offset = 0;
-		var->green.offset = 0;
-		var->blue.offset = 0;
-		var->red.length = 8;
-		var->green.length = 8;
-		var->blue.length = 8;
-		var->transp.length = 0;
-		var->transp.offset = 0;
-		break;
-	case 15:
-		var->red.offset = 10;
-		var->green.offset = 5;
-		var->blue.offset = 0;
-		var->red.length = 5;
-		var->green.length = 5;
-		var->blue.length = 5;
-		var->transp.length = 1;
-		var->transp.offset = 15;
-		break;
-	case 16:
-		var->red.offset = 11;
-		var->green.offset = 5;
-		var->blue.offset = 0;
-		var->red.length = 5;
-		var->green.length = 6;
-		var->blue.length = 5;
-		var->transp.length = 0;
-		var->transp.offset = 0;
-		break;
-	case 24:
-		var->red.offset = 16;
-		var->green.offset = 8;
-		var->blue.offset = 0;
-		var->red.length = 8;
-		var->green.length = 8;
-		var->blue.length = 8;
-		var->transp.length = 0;
-		var->transp.offset = 0;
-		break;
-	case 32:
-		var->red.offset = 16;
-		var->green.offset = 8;
-		var->blue.offset = 0;
-		var->red.length = 8;
-		var->green.length = 8;
-		var->blue.length = 8;
-		var->transp.length = 8;
-		var->transp.offset = 24;
-		break;
-	default:
+	/*
+	 * drm fbdev emulation doesn't support changing the pixel format at all,
+	 * so reject all pixel format changing requests.
+	 */
+	if (!drm_fb_pixel_format_equal(var, &info->var)) {
+		DRM_DEBUG("fbdev emulation doesn't support changing the pixel format\n");
 		return -EINVAL;
 	}
+
 	return 0;
 }
 EXPORT_SYMBOL(drm_fb_helper_check_var);