acpi: Add a function to get a device path and scope

Add a function to build up the ACPI path for a device and another for its
scope.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

lib/acpi/Makefile

@@ -1,4 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0+
 #
 
+obj-y += acpi_device.o
 obj-y += acpi_table.o

lib/acpi/acpi_device.c

@@ -0,0 +1,83 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Generation of tables for particular device types
+ *
+ * Copyright 2019 Google LLC
+ * Mostly taken from coreboot file of the same name
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <log.h>
+#include <acpi/acpi_device.h>
+#include <dm/acpi.h>
+
+/**
+ * acpi_device_path_fill() - Find the root device and build a path from there
+ *
+ * This recursively reaches back to the root device and progressively adds path
+ * elements until the device is reached.
+ *
+ * @dev: Device to return path of
+ * @buf: Buffer to hold the path
+ * @buf_len: Length of buffer
+ * @cur: Current position in the buffer
+ * @return new position in buffer after adding @dev, or -ve on error
+ */
+static int acpi_device_path_fill(const struct udevice *dev, char *buf,
+				 size_t buf_len, int cur)
+{
+	char name[ACPI_NAME_MAX];
+	int next = 0;
+	int ret;
+
+	ret = acpi_get_name(dev, name);
+	if (ret)
+		return ret;
+
+	/*
+	 * Make sure this name segment will fit, including the path segment
+	 * separator and possible NULL terminator, if this is the last segment.
+	 */
+	if (cur + strlen(name) + 2 > buf_len)
+		return -ENOSPC;
+
+	/* Walk up the tree to the root device */
+	if (dev_get_parent(dev)) {
+		next = acpi_device_path_fill(dev_get_parent(dev), buf, buf_len,
+					     cur);
+		if (next < 0)
+			return next;
+	}
+
+	/* Fill in the path from the root device */
+	next += snprintf(buf + next, buf_len - next, "%s%s",
+			 dev_get_parent(dev) && *name ? "." : "", name);
+
+	return next;
+}
+
+int acpi_device_path(const struct udevice *dev, char *buf, int maxlen)
+{
+	int ret;
+
+	ret = acpi_device_path_fill(dev, buf, maxlen, 0);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+int acpi_device_scope(const struct udevice *dev, char *scope, int maxlen)
+{
+	int ret;
+
+	if (!dev_get_parent(dev))
+		return log_msg_ret("noparent", -EINVAL);
+
+	ret = acpi_device_path_fill(dev_get_parent(dev), scope, maxlen, 0);
+	if (ret < 0)
+		return log_msg_ret("fill", ret);
+
+	return 0;
+}