drm: apple: make plane zpos immutable

Userspace cannot be trusted to give us a sane zpos value, but given DCP's
requirement that the primary plane always be the bottommost surface, we
can't rely on drm_atomic_normalize_zpos() to do the job for us either.

Make the zpos property immutable, and keep the primary plane at zpos 0.

Signed-off-by: James Calligeros <jcalligeros99@gmail.com>

Author: chadmed

drivers/gpu/drm/apple/apple_drv.c

@@ -20,6 +20,7 @@
 
 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
+#include <drm/drm_blend.h>
 #include <drm/clients/drm_client_setup.h>
 #include <drm/drm_crtc.h>
 #include <drm/drm_drv.h>
@@ -431,17 +432,27 @@ static int apple_probe_per_dcp(struct device *dev,
 	struct apple_encoder *enc;
 	struct drm_plane *planes[DCP_MAX_PLANES];
 	int ret, i;
+	int immutable_zpos = 0;
 
 	planes[0] = apple_plane_init(drm, 1U << num, DRM_PLANE_TYPE_PRIMARY);
 	if (IS_ERR(planes[0]))
 		return PTR_ERR(planes[0]);
+	ret = drm_plane_create_zpos_immutable_property(planes[0], immutable_zpos);
+	if (ret) {
+		return ret;
+	}
 
 
 	/* Set up our other planes */
 	for (i = 1; i < DCP_MAX_PLANES; i++) {
 		planes[i] = apple_plane_init(drm, 1U << num, DRM_PLANE_TYPE_OVERLAY);
 		if (IS_ERR(planes[i]))
 			return PTR_ERR(planes[i]);
+		immutable_zpos++;
+		ret = drm_plane_create_zpos_immutable_property(planes[i], immutable_zpos);
+		if (ret) {
+			return ret;
+		}
 	}
 
 	/*

drivers/gpu/drm/apple/iomfb_template.c

@@ -1316,7 +1316,7 @@ void DCP_FW_NAME(iomfb_flush)(struct apple_dcp *dcp, struct drm_crtc *crtc, stru
 		 * also unusable on some machines, so ignore it.
 		 */
 
-		l = MAX_BLEND_SURFACES - new_state->zpos;
+		l = MAX_BLEND_SURFACES - new_state->normalized_zpos;
 
 		WARN_ON(l > MAX_BLEND_SURFACES);