boot/efi: handle /chosen/stdout-path

Change-Id: I08ebadf274448e1319cc8b0666beaf709382c00f
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5143
Reviewed-by: Fredrik Holmqvist <[email protected]>
Tested-by: Commit checker robot <[email protected]>

src/system/boot/platform/efi/dtb.cpp

@@ -460,8 +460,6 @@ dtb_handle_fdt(const void* fdt, int node)
 	if (compatible == NULL)
 		return;
 
-	// TODO: We should check for the "chosen" uart and prioritize that one
-
 	// check for a uart if we don't have one
 	uart_info &uart = gKernelArgs.arch_args.uart;
 	if (uart.kind[0] == 0) {
@@ -487,6 +485,34 @@ dtb_handle_fdt(const void* fdt, int node)
 }
 
 
+static void
+dtb_handle_chosen_node(const void *fdt)
+{
+	int chosen = fdt_path_offset(fdt, "/chosen");
+	if (chosen < 0)
+		return;
+
+	int len;
+	const char *stdoutPath = (const char *)fdt_getprop(fdt, chosen, "stdout-path", &len);
+	if (stdoutPath == NULL)
+		return;
+
+	// stdout-path can optionally contain a ":" separator character
+	// The part after the ":" character specifies the UART configuration
+	// We can ignore it here as the UART should be already initialized
+	// by the UEFI firmware (e.g. U-Boot or TianoCore)
+
+	char *separator = strchr(stdoutPath, ':');
+	int namelen = (separator == NULL) ? len - 1 : separator - stdoutPath;
+
+	int stdoutNode = fdt_path_offset_namelen(fdt, stdoutPath, namelen);
+	if (stdoutNode < 0)
+		return;
+
+	dtb_handle_fdt(fdt, stdoutNode);
+}
+
+
 void
 dtb_init()
 {
@@ -519,6 +545,8 @@ dtb_init()
 		if (false)
 			DumpFdt(sDtbTable);
 
+		dtb_handle_chosen_node(sDtbTable);
+
 		int node = -1;
 		int depth = -1;
 		while ((node = fdt_next_node(sDtbTable, node, &depth)) >= 0 && depth >= 0) {