drm/modes: Add of_get_drm_panel_display_mode()

Add a function to get a drm_display_mode from a panel-timing
device tree subnode.

Suggested-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220227124713.39766-4-noralf@tronnes.org

drivers/gpu/drm/drm_modes.c

@@ -35,6 +35,7 @@
 #include <linux/list_sort.h>
 #include <linux/export.h>
 
+#include <video/of_display_timing.h>
 #include <video/of_videomode.h>
 #include <video/videomode.h>
 
@@ -727,6 +728,54 @@ int of_get_drm_display_mode(struct device_node *np,
 	return 0;
 }
 EXPORT_SYMBOL_GPL(of_get_drm_display_mode);
+
+/**
+ * of_get_drm_panel_display_mode - get a panel-timing drm_display_mode from devicetree
+ * @np: device_node with the panel-timing specification
+ * @dmode: will be set to the return value
+ * @bus_flags: information about pixelclk, sync and DE polarity
+ *
+ * The Device Tree properties width-mm and height-mm will be read and set on
+ * the display mode if they are present.
+ *
+ * Returns:
+ * Zero on success, negative error code on failure.
+ */
+int of_get_drm_panel_display_mode(struct device_node *np,
+				  struct drm_display_mode *dmode, u32 *bus_flags)
+{
+	u32 width_mm = 0, height_mm = 0;
+	struct display_timing timing;
+	struct videomode vm;
+	int ret;
+
+	ret = of_get_display_timing(np, "panel-timing", &timing);
+	if (ret)
+		return ret;
+
+	videomode_from_timing(&timing, &vm);
+
+	memset(dmode, 0, sizeof(*dmode));
+	drm_display_mode_from_videomode(&vm, dmode);
+	if (bus_flags)
+		drm_bus_flags_from_videomode(&vm, bus_flags);
+
+	ret = of_property_read_u32(np, "width-mm", &width_mm);
+	if (ret && ret != -EINVAL)
+		return ret;
+
+	ret = of_property_read_u32(np, "height-mm", &height_mm);
+	if (ret && ret != -EINVAL)
+		return ret;
+
+	dmode->width_mm = width_mm;
+	dmode->height_mm = height_mm;
+
+	drm_mode_debug_printmodeline(dmode);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(of_get_drm_panel_display_mode);
 #endif /* CONFIG_OF */
 #endif /* CONFIG_VIDEOMODE_HELPERS */
 

include/drm/drm_modes.h

@@ -466,6 +466,8 @@ void drm_bus_flags_from_videomode(const struct videomode *vm, u32 *bus_flags);
 int of_get_drm_display_mode(struct device_node *np,
 			    struct drm_display_mode *dmode, u32 *bus_flags,
 			    int index);
+int of_get_drm_panel_display_mode(struct device_node *np,
+				  struct drm_display_mode *dmode, u32 *bus_flags);
 #else
 static inline int of_get_drm_display_mode(struct device_node *np,
 					  struct drm_display_mode *dmode,
@@ -473,6 +475,12 @@ static inline int of_get_drm_display_mode(struct device_node *np,
 {
 	return -EINVAL;
 }
+
+static inline int of_get_drm_panel_display_mode(struct device_node *np,
+						struct drm_display_mode *dmode, u32 *bus_flags)
+{
+	return -EINVAL;
+}
 #endif
 
 void drm_mode_set_name(struct drm_display_mode *mode);