firewire: core: detect model name for legacy layout of configuration ROM

As the part of support for legacy layout of configuration ROM, this
commit traverses vendor directory as well as root directory when showing
device attribute for node device. This change expects 'model_name'
attribute appears in node device, however it is probable to see the other
types of descriptor leaf if the vendor directory includes.

Suggested-by: Adam Goldman <adamg@pobox.com>
Link: https://lore.kernel.org/r/20231221134849.603857-8-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>

Author: takaswie

drivers/firewire/core-device.c

@@ -317,17 +317,29 @@ static ssize_t show_text_leaf(struct device *dev,
 {
 	struct config_rom_attribute *attr =
 		container_of(dattr, struct config_rom_attribute, attr);
-	const u32 *dir;
+	const u32 *directories[] = {NULL, NULL};
 	size_t bufsize;
 	char dummy_buf[2];
-	int ret;
+	int i, ret = -ENOENT;
 
 	down_read(&fw_device_rwsem);
 
-	if (is_fw_unit(dev))
-		dir = fw_unit(dev)->directory;
-	else
-		dir = fw_device(dev)->config_rom + ROOT_DIR_OFFSET;
+	if (is_fw_unit(dev)) {
+		directories[0] = fw_unit(dev)->directory;
+	} else {
+		const u32 *root_directory = fw_device(dev)->config_rom + ROOT_DIR_OFFSET;
+		const u32 *vendor_directory = search_directory(root_directory, CSR_VENDOR);
+
+		if (!vendor_directory) {
+			directories[0] = root_directory;
+		} else {
+			// Legacy layout of configuration ROM described in Annex 1 of
+			// 'Configuration ROM for AV/C Devices 1.0 (December 12, 2000, 1394
+			// Trading Association, TA Document 1999027)'.
+			directories[0] = root_directory;
+			directories[1] = vendor_directory;
+		}
+	}
 
 	if (buf) {
 		bufsize = PAGE_SIZE - 1;
@@ -336,7 +348,12 @@ static ssize_t show_text_leaf(struct device *dev,
 		bufsize = 1;
 	}
 
-	ret = fw_csr_string(dir, attr->key, buf, bufsize);
+	for (i = 0; i < ARRAY_SIZE(directories) && !!directories[i]; ++i) {
+		int result = fw_csr_string(directories[i], attr->key, buf, bufsize);
+		// Detected.
+		if (result >= 0)
+			ret = result;
+	}
 
 	if (ret >= 0) {
 		/* Strip trailing whitespace and add newline. */

drivers/firewire/device-attribute-test.c

@@ -206,8 +206,9 @@ static void device_attr_legacy_avc(struct kunit *test)
 	// Descriptor leaf entry for vendor is not found.
 	KUNIT_EXPECT_LT(test, show_text_leaf(node_dev, &config_rom_attributes[5].attr, buf), 0);
 
-	// Descriptor leaf entry for model is not found.
-	KUNIT_EXPECT_LT(test, show_text_leaf(node_dev, &config_rom_attributes[6].attr, buf), 0);
+	// Descriptor leaf entry for model is found.
+	KUNIT_EXPECT_GT(test, show_text_leaf(node_dev, &config_rom_attributes[6].attr, buf), 0);
+	KUNIT_EXPECT_STREQ(test, buf, "ABCDEFGHIJ\n");
 
 	// For entries in unit 0 directory.