drm: Move drm_plane_helper_check_state() into drm_atomic_helper.c

drm_plane_helper_check_update() isn't a transitional helper, so let's
rename it to drm_atomic_helper_check_plane_state() and move it into
drm_atomic_helper.c.

v2: Fix the WARNs about plane_state->crtc matching crtc_state->crtc

Cc: Daniel Vetter <daniel@ffwll.ch>
Suggested-by: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171101201619.6175-1-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_atomic_helper.c

@@ -695,6 +695,100 @@ drm_atomic_helper_check_modeset(struct drm_device *dev,
 }
 EXPORT_SYMBOL(drm_atomic_helper_check_modeset);
 
+/**
+ * drm_atomic_helper_check_plane_state() - Check plane state for validity
+ * @plane_state: plane state to check
+ * @crtc_state: crtc state to check
+ * @clip: integer clipping coordinates
+ * @min_scale: minimum @src:@dest scaling factor in 16.16 fixed point
+ * @max_scale: maximum @src:@dest scaling factor in 16.16 fixed point
+ * @can_position: is it legal to position the plane such that it
+ *                doesn't cover the entire crtc?  This will generally
+ *                only be false for primary planes.
+ * @can_update_disabled: can the plane be updated while the crtc
+ *                       is disabled?
+ *
+ * Checks that a desired plane update is valid, and updates various
+ * bits of derived state (clipped coordinates etc.). Drivers that provide
+ * their own plane handling rather than helper-provided implementations may
+ * still wish to call this function to avoid duplication of error checking
+ * code.
+ *
+ * RETURNS:
+ * Zero if update appears valid, error code on failure
+ */
+int drm_atomic_helper_check_plane_state(struct drm_plane_state *plane_state,
+					const struct drm_crtc_state *crtc_state,
+					const struct drm_rect *clip,
+					int min_scale,
+					int max_scale,
+					bool can_position,
+					bool can_update_disabled)
+{
+	struct drm_framebuffer *fb = plane_state->fb;
+	struct drm_rect *src = &plane_state->src;
+	struct drm_rect *dst = &plane_state->dst;
+	unsigned int rotation = plane_state->rotation;
+	int hscale, vscale;
+
+	WARN_ON(plane_state->crtc && plane_state->crtc != crtc_state->crtc);
+
+	*src = drm_plane_state_src(plane_state);
+	*dst = drm_plane_state_dest(plane_state);
+
+	if (!fb) {
+		plane_state->visible = false;
+		return 0;
+	}
+
+	/* crtc should only be NULL when disabling (i.e., !fb) */
+	if (WARN_ON(!plane_state->crtc)) {
+		plane_state->visible = false;
+		return 0;
+	}
+
+	if (!crtc_state->enable && !can_update_disabled) {
+		DRM_DEBUG_KMS("Cannot update plane of a disabled CRTC.\n");
+		return -EINVAL;
+	}
+
+	drm_rect_rotate(src, fb->width << 16, fb->height << 16, rotation);
+
+	/* Check scaling */
+	hscale = drm_rect_calc_hscale(src, dst, min_scale, max_scale);
+	vscale = drm_rect_calc_vscale(src, dst, min_scale, max_scale);
+	if (hscale < 0 || vscale < 0) {
+		DRM_DEBUG_KMS("Invalid scaling of plane\n");
+		drm_rect_debug_print("src: ", &plane_state->src, true);
+		drm_rect_debug_print("dst: ", &plane_state->dst, false);
+		return -ERANGE;
+	}
+
+	plane_state->visible = drm_rect_clip_scaled(src, dst, clip, hscale, vscale);
+
+	drm_rect_rotate_inv(src, fb->width << 16, fb->height << 16, rotation);
+
+	if (!plane_state->visible)
+		/*
+		 * Plane isn't visible; some drivers can handle this
+		 * so we just return success here.  Drivers that can't
+		 * (including those that use the primary plane helper's
+		 * update function) will return an error from their
+		 * update_plane handler.
+		 */
+		return 0;
+
+	if (!can_position && !drm_rect_equals(dst, clip)) {
+		DRM_DEBUG_KMS("Plane must cover entire CRTC\n");
+		drm_rect_debug_print("dst: ", dst, false);
+		drm_rect_debug_print("clip: ", clip, false);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(drm_atomic_helper_check_plane_state);
+
 /**
  * drm_atomic_helper_check_planes - validate state object for planes changes
  * @dev: DRM device