drm_modes: add of_videomode helpers

Add helper to get drm_display_mode from devicetree.

Signed-off-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Reviewed-by: Thierry Reding <thierry.reding@avionic-design.de>
Acked-by: Thierry Reding <thierry.reding@avionic-design.de>
Tested-by: Thierry Reding <thierry.reding@avionic-design.de>
Tested-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Afzal Mohammed <Afzal@ti.com>
Tested-by: Rob Clark <robclark@gmail.com>
Tested-by: Leela Krishna Amudala <leelakrishna.a@gmail.com>

drivers/gpu/drm/drm_modes.c

@@ -35,6 +35,7 @@
 #include <linux/export.h>
 #include <drm/drmP.h>
 #include <drm/drm_crtc.h>
+#include <video/of_videomode.h>
 #include <video/videomode.h>
 
 /**
@@ -541,6 +542,38 @@ int drm_display_mode_from_videomode(const struct videomode *vm,
 EXPORT_SYMBOL_GPL(drm_display_mode_from_videomode);
 #endif
 
+#if IS_ENABLED(CONFIG_OF_VIDEOMODE)
+/**
+ * of_get_drm_display_mode - get a drm_display_mode from devicetree
+ * @np: device_node with the timing specification
+ * @dmode: will be set to the return value
+ * @index: index into the list of display timings in devicetree
+ *
+ * This function is expensive and should only be used, if only one mode is to be
+ * read from DT. To get multiple modes start with of_get_display_timings and
+ * work with that instead.
+ */
+int of_get_drm_display_mode(struct device_node *np,
+			    struct drm_display_mode *dmode, int index)
+{
+	struct videomode vm;
+	int ret;
+
+	ret = of_get_videomode(np, &vm, index);
+	if (ret)
+		return ret;
+
+	drm_display_mode_from_videomode(&vm, dmode);
+
+	pr_debug("%s: got %dx%d display mode from %s\n",
+		of_node_full_name(np), vm.hactive, vm.vactive, np->name);
+	drm_mode_debug_printmodeline(dmode);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(of_get_drm_display_mode);
+#endif
+
 /**
  * drm_mode_set_name - set the name on a mode
  * @mode: name will be set in this mode

include/drm/drmP.h

@@ -85,6 +85,7 @@ struct module;
 struct drm_file;
 struct drm_device;
 
+struct device_node;
 struct videomode;
 
 #include <drm/drm_os_linux.h>
@@ -1460,6 +1461,9 @@ drm_mode_create_from_cmdline_mode(struct drm_device *dev,
 
 extern int drm_display_mode_from_videomode(const struct videomode *vm,
 					   struct drm_display_mode *dmode);
+extern int of_get_drm_display_mode(struct device_node *np,
+				   struct drm_display_mode *dmode,
+				   int index);
 
 /* Modesetting support */
 extern void drm_vblank_pre_modeset(struct drm_device *dev, int crtc);