drm_of_lvds_get_dual_link_pixel_order() gets LVDS dual-link source pixel
order.  Similar to it, add it's counterpart function
drm_of_lvds_get_dual_link_pixel_order_sink() to get LVDS dual-link sink
pixel order.

Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Liu Ying <victor.liu@nxp.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
---
v4:
* Collect Dmitry's R-b tag.

v3:
* New patch.  (Dmitry)

 drivers/gpu/drm/drm_of.c | 76 ++++++++++++++++++++++++++++++++++------
 include/drm/drm_of.h     |  9 +++++
 2 files changed, 74 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
index 89863a35c731..5c2abc9eca9c 100644
--- a/drivers/gpu/drm/drm_of.c
+++ b/drivers/gpu/drm/drm_of.c
@@ -341,8 +341,23 @@ static int drm_of_lvds_get_remote_pixels_type(
 	return pixels_type;
 }
 
+static int __drm_of_lvds_get_dual_link_pixel_order(int p1_pt, int p2_pt)
+{
+	/*
+	 * A valid dual-lVDS bus is found when one port is marked with
+	 * "dual-lvds-even-pixels", and the other port is marked with
+	 * "dual-lvds-odd-pixels", bail out if the markers are not right.
+	 */
+	if (p1_pt + p2_pt != DRM_OF_LVDS_EVEN + DRM_OF_LVDS_ODD)
+		return -EINVAL;
+
+	return p1_pt == DRM_OF_LVDS_EVEN ?
+		DRM_LVDS_DUAL_LINK_EVEN_ODD_PIXELS :
+		DRM_LVDS_DUAL_LINK_ODD_EVEN_PIXELS;
+}
+
 /**
- * drm_of_lvds_get_dual_link_pixel_order - Get LVDS dual-link pixel order
+ * drm_of_lvds_get_dual_link_pixel_order - Get LVDS dual-link source pixel order
  * @port1: First DT port node of the Dual-link LVDS source
  * @port2: Second DT port node of the Dual-link LVDS source
  *
@@ -387,19 +402,58 @@ int drm_of_lvds_get_dual_link_pixel_order(const struct device_node *port1,
 	if (remote_p2_pt < 0)
 		return remote_p2_pt;
 
-	/*
-	 * A valid dual-lVDS bus is found when one remote port is marked with
-	 * "dual-lvds-even-pixels", and the other remote port is marked with
-	 * "dual-lvds-odd-pixels", bail out if the markers are not right.
-	 */
-	if (remote_p1_pt + remote_p2_pt != DRM_OF_LVDS_EVEN + DRM_OF_LVDS_ODD)
+	return __drm_of_lvds_get_dual_link_pixel_order(remote_p1_pt, remote_p2_pt);
+}
+EXPORT_SYMBOL_GPL(drm_of_lvds_get_dual_link_pixel_order);
+
+/**
+ * drm_of_lvds_get_dual_link_pixel_order_sink - Get LVDS dual-link sink pixel order
+ * @port1: First DT port node of the Dual-link LVDS sink
+ * @port2: Second DT port node of the Dual-link LVDS sink
+ *
+ * An LVDS dual-link connection is made of two links, with even pixels
+ * transitting on one link, and odd pixels on the other link. This function
+ * returns, for two ports of an LVDS dual-link sink, which port shall transmit
+ * the even and odd pixels, based on the requirements of the sink.
+ *
+ * The pixel order is determined from the dual-lvds-even-pixels and
+ * dual-lvds-odd-pixels properties in the sink's DT port nodes. If those
+ * properties are not present, or if their usage is not valid, this function
+ * returns -EINVAL.
+ *
+ * If either port is not connected, this function returns -EPIPE.
+ *
+ * @port1 and @port2 are typically DT sibling nodes, but may have different
+ * parents when, for instance, two separate LVDS decoders receive the even and
+ * odd pixels.
+ *
+ * Return:
+ * * DRM_LVDS_DUAL_LINK_EVEN_ODD_PIXELS - @port1 receives even pixels and @port2
+ *   receives odd pixels
+ * * DRM_LVDS_DUAL_LINK_ODD_EVEN_PIXELS - @port1 receives odd pixels and @port2
+ *   receives even pixels
+ * * -EINVAL - @port1 or @port2 are NULL
+ * * -EPIPE - when @port1 or @port2 are not connected
+ */
+int drm_of_lvds_get_dual_link_pixel_order_sink(struct device_node *port1,
+					       struct device_node *port2)
+{
+	int sink_p1_pt, sink_p2_pt;
+
+	if (!port1 || !port2)
 		return -EINVAL;
 
-	return remote_p1_pt == DRM_OF_LVDS_EVEN ?
-		DRM_LVDS_DUAL_LINK_EVEN_ODD_PIXELS :
-		DRM_LVDS_DUAL_LINK_ODD_EVEN_PIXELS;
+	sink_p1_pt = drm_of_lvds_get_port_pixels_type(port1);
+	if (!sink_p1_pt)
+		return -EPIPE;
+
+	sink_p2_pt = drm_of_lvds_get_port_pixels_type(port2);
+	if (!sink_p2_pt)
+		return -EPIPE;
+
+	return __drm_of_lvds_get_dual_link_pixel_order(sink_p1_pt, sink_p2_pt);
 }
-EXPORT_SYMBOL_GPL(drm_of_lvds_get_dual_link_pixel_order);
+EXPORT_SYMBOL_GPL(drm_of_lvds_get_dual_link_pixel_order_sink);
 
 /**
  * drm_of_lvds_get_data_mapping - Get LVDS data mapping
diff --git a/include/drm/drm_of.h b/include/drm/drm_of.h
index 02d1cdd7f798..7f0256dae3f1 100644
--- a/include/drm/drm_of.h
+++ b/include/drm/drm_of.h
@@ -52,6 +52,8 @@ int drm_of_find_panel_or_bridge(const struct device_node *np,
 				struct drm_bridge **bridge);
 int drm_of_lvds_get_dual_link_pixel_order(const struct device_node *port1,
 					  const struct device_node *port2);
+int drm_of_lvds_get_dual_link_pixel_order_sink(struct device_node *port1,
+					       struct device_node *port2);
 int drm_of_lvds_get_data_mapping(const struct device_node *port);
 int drm_of_get_data_lanes_count(const struct device_node *endpoint,
 				const unsigned int min, const unsigned int max);
@@ -109,6 +111,13 @@ drm_of_lvds_get_dual_link_pixel_order(const struct device_node *port1,
 	return -EINVAL;
 }
 
+static inline int
+drm_of_lvds_get_dual_link_pixel_order_sink(struct device_node *port1,
+					   struct device_node *port2)
+{
+	return -EINVAL;
+}
+
 static inline int
 drm_of_lvds_get_data_mapping(const struct device_node *port)
 {
-- 
2.34.1