drm/i915: Add intel_atomic_get_crtc_state() helper function

The pattern of getting the crtc state with drm_atomic_get_crtc_state()
and then converting it to intel_crtc_state will repeat quite often in
the following patches, so add a helper function to save some typing.

v2: Fix upcasting so that crtc_state base field could be moved. (Daniel)
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_drv.h

@@ -35,6 +35,7 @@
 #include <drm/drm_fb_helper.h>
 #include <drm/drm_dp_mst_helper.h>
 #include <drm/drm_rect.h>
+#include <drm/drm_atomic.h>
 
 #define DIV_ROUND_CLOSEST_ULL(ll, d)	\
 ({ unsigned long long _tmp = (ll)+(d)/2; do_div(_tmp, d); _tmp; })
@@ -562,6 +563,7 @@ struct cxsr_latency {
 };
 
 #define to_intel_crtc(x) container_of(x, struct intel_crtc, base)
+#define to_intel_crtc_state(x) container_of(x, struct intel_crtc_state, base)
 #define to_intel_connector(x) container_of(x, struct intel_connector, base)
 #define to_intel_encoder(x) container_of(x, struct intel_encoder, base)
 #define to_intel_framebuffer(x) container_of(x, struct intel_framebuffer, base)
@@ -1303,6 +1305,17 @@ int intel_connector_atomic_get_property(struct drm_connector *connector,
 struct drm_crtc_state *intel_crtc_duplicate_state(struct drm_crtc *crtc);
 void intel_crtc_destroy_state(struct drm_crtc *crtc,
 			       struct drm_crtc_state *state);
+static inline struct intel_crtc_state *
+intel_atomic_get_crtc_state(struct drm_atomic_state *state,
+			    struct intel_crtc *crtc)
+{
+	struct drm_crtc_state *crtc_state;
+	crtc_state = drm_atomic_get_crtc_state(state, &crtc->base);
+	if (IS_ERR(crtc_state))
+		return ERR_PTR(PTR_ERR(crtc_state));
+
+	return to_intel_crtc_state(crtc_state);
+}
 
 /* intel_atomic_plane.c */
 struct intel_plane_state *intel_create_plane_state(struct drm_plane *plane);