drm: simplify the locking in the GETCRTC ioctl

No need to grab both plane and crtc locks at the same time, we can do
them one after the other. If userspace races it'll get what it
deserves either way.

This removes another user of drm_modeset_lock_crtc. There's only one
left.

v2: Make sure all access to primary->state is properly protected
(Harry).

Cc: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170328070145.21520-1-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_crtc.c

@@ -406,9 +406,9 @@ int drm_mode_getcrtc(struct drm_device *dev,
 	if (!crtc)
 		return -ENOENT;
 
-	drm_modeset_lock_crtc(crtc, crtc->primary);
 	crtc_resp->gamma_size = crtc->gamma_size;
 
+	drm_modeset_lock(&crtc->primary->mutex, NULL);
 	if (crtc->primary->state && crtc->primary->state->fb)
 		crtc_resp->fb_id = crtc->primary->state->fb->base.id;
 	else if (!crtc->primary->state && crtc->primary->fb)
@@ -416,9 +416,14 @@ int drm_mode_getcrtc(struct drm_device *dev,
 	else
 		crtc_resp->fb_id = 0;
 
-	if (crtc->state) {
+	if (crtc->primary->state) {
 		crtc_resp->x = crtc->primary->state->src_x >> 16;
 		crtc_resp->y = crtc->primary->state->src_y >> 16;
+	}
+	drm_modeset_unlock(&crtc->primary->mutex);
+
+	drm_modeset_lock(&crtc->mutex, NULL);
+	if (crtc->state) {
 		if (crtc->state->enable) {
 			drm_mode_convert_to_umode(&crtc_resp->mode, &crtc->state->mode);
 			crtc_resp->mode_valid = 1;
@@ -437,7 +442,7 @@ int drm_mode_getcrtc(struct drm_device *dev,
 			crtc_resp->mode_valid = 0;
 		}
 	}
-	drm_modeset_unlock_crtc(crtc);
+	drm_modeset_unlock(&crtc->mutex);
 
 	return 0;
 }

drivers/gpu/drm/i915/intel_display.c

@@ -12468,6 +12468,11 @@ static int intel_atomic_check(struct drm_device *dev,
 	ret = drm_atomic_helper_check_modeset(dev, state);
 	if (ret)
 		return ret;
+	/* enocder->atomic_check might upgrade some crtc to a full modeset */
+	ret = drm_atomic_helper_check_modeset(dev, state);
+	if (ret)
+		return ret;
+
 
 	for_each_oldnew_crtc_in_state(state, crtc, old_crtc_state, crtc_state, i) {
 		struct intel_crtc_state *pipe_config =