fdt: add new fdt_fixup_display function to configure display

Add 'fdt_fixup_display' function to fixup device-tree native-mode property
of display-timings node to select timings for a specific display.
This is useful if a device-tree has configurations for multiple
display timings for undetectable displays.

see kernel Documentation/devicetree/bindings/video/display-timing.txt

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Acked-by: Simon Glass <sjg@chromium.org>

common/fdt_support.c

@@ -1560,3 +1560,32 @@ int fdt_setup_simplefb_node(void *fdt, int node, u64 base_address, u32 width,
 
 	return 0;
 }
+
+/*
+ * Update native-mode in display-timings from display environment variable.
+ * The node to update are specified by path.
+ */
+int fdt_fixup_display(void *blob, const char *path, const char *display)
+{
+	int off, toff;
+
+	if (!display || !path)
+		return -FDT_ERR_NOTFOUND;
+
+	toff = fdt_path_offset(blob, path);
+	if (toff >= 0)
+		toff = fdt_subnode_offset(blob, toff, "display-timings");
+	if (toff < 0)
+		return toff;
+
+	for (off = fdt_first_subnode(blob, toff);
+	     off >= 0;
+	     off = fdt_next_subnode(blob, off)) {
+		uint32_t h = fdt_get_phandle(blob, off);
+		debug("%s:0x%x\n", fdt_get_name(blob, off, NULL),
+		      fdt32_to_cpu(h));
+		if (strcasecmp(fdt_get_name(blob, off, NULL), display) == 0)
+			return fdt_setprop_u32(blob, toff, "native-mode", h);
+	}
+	return toff;
+}

include/fdt_support.h

@@ -47,6 +47,19 @@ int fdt_find_and_setprop(void *fdt, const char *node, const char *prop,
 			 const void *val, int len, int create);
 void fdt_fixup_qe_firmware(void *fdt);
 
+/**
+ * Update native-mode property of display-timings node to the phandle
+ * of the timings matching a display by name (case insensitive).
+ *
+ * see kernel Documentation/devicetree/bindings/video/display-timing.txt
+ *
+ * @param blob		FDT blob to update
+ * @param path		path within dt
+ * @param display	name of display timing to match
+ * @return 0 if ok, or -FDT_ERR_... on error
+ */
+int fdt_fixup_display(void *blob, const char *path, const char *display);
+
 #if defined(CONFIG_HAS_FSL_DR_USB) || defined(CONFIG_HAS_FSL_MPH_USB)
 void fdt_fixup_dr_usb(void *blob, bd_t *bd);
 #else