drm: Handle aspect ratio info in legacy modeset path

If the user-space does not support aspect-ratio, and requests for a
modeset with mode having aspect ratio bits set, then the given
user-mode must be rejected. Secondly, while preparing a user-mode from
kernel mode, the aspect-ratio info must not be given, if aspect-ratio
is not supported by the user.

This patch:
1. rejects the modes with aspect-ratio info, during modeset, if the
   user does not support aspect ratio.
2. does not load the aspect-ratio info in user-mode structure, if
   aspect ratio is not supported.
3. adds helper functions for determining if aspect-ratio is expected
   in user-mode and for allowing/disallowing the aspect-ratio, if its
   not expected.
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>

V3: Addressed review comments from Ville:
    Do not corrupt the current crtc state by updating aspect-ratio on
    the fly.
V4: rebase
V5: As suggested by Ville, rejected the modeset calls for modes with
    aspect ratio, if the user does not set aspect-ratio cap.
V6: Used the helper functions for determining if aspect-ratio is
    expected in the user-mode.
V7: rebase
V8: rebase
V9: rebase
V10: Modified the commit-message
V11: rebase
V12: Merged the patch for adding aspect-ratio helper functions
     with this patch.
V13: Minor modifications as suggested by Ville.
V14: Removed helper functions, as they were used only once in legacy
     modeset path, as suggested by Daniel Vetter.
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1525777785-9740-8-git-send-email-ankit.k.nautiyal@intel.com

drivers/gpu/drm/drm_crtc.c

@@ -449,6 +449,8 @@ int drm_mode_getcrtc(struct drm_device *dev,
 			crtc_resp->mode_valid = 0;
 		}
 	}
+	if (!file_priv->aspect_ratio_allowed)
+		crtc_resp->mode.flags &= ~DRM_MODE_FLAG_PIC_AR_MASK;
 	drm_modeset_unlock(&crtc->mutex);
 
 	return 0;
@@ -628,6 +630,13 @@ int drm_mode_setcrtc(struct drm_device *dev, void *data,
 			ret = -ENOMEM;
 			goto out;
 		}
+		if (!file_priv->aspect_ratio_allowed &&
+		    (crtc_req->mode.flags & DRM_MODE_FLAG_PIC_AR_MASK) != DRM_MODE_FLAG_PIC_AR_NONE) {
+			DRM_DEBUG_KMS("Unexpected aspect-ratio flag bits\n");
+			ret = -EINVAL;
+			goto out;
+		}
+
 
 		ret = drm_mode_convert_umode(dev, mode, &crtc_req->mode);
 		if (ret) {