linux-kernel - [PATCH v2 8/8] firewire: core: change modalias of unit device with backward incompatibility

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Message-Id: <20231221134849.603857-9-o-takashi@sakamocchi.jp>
Date: Thu, 21 Dec 2023 22:48:49 +0900
From: Takashi Sakamoto <o-takashi@...amocchi.jp>
To: linux1394-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Cc: adamg@...ox.com
Subject: [PATCH v2 8/8] firewire: core: change modalias of unit device with backward incompatibility

As the last part of support for legacy layout of configuration ROM, this
commit traverses vendor directory as well as root directory when
constructing modalias for unit device. The change brings loss of backward
compatibility since it can fill model field ('mo') which is 0 at current
implementation in the case. However, we can be optimistic against
regression for unit drivers in kernel, due to some points:

1. ALSA drivers for audio and music units use the model fields to match
   device, however all of supported devices does not have such legacy
   layout.
2. the other unit drivers (e.g. sbp2) does not use the model field to
   match device.

The rest of concern is user space application. The most of applications
just take care of node device and does not use the modalias of unit
device, thus the change does not affect to them. But systemd project is
known to get affects from the change since it includes hwdb to take udev
to configure fw character device conveniently. I have a plan to work for
systemd so that the access permission of character device could be kept
across the change.

Signed-off-by: Takashi Sakamoto <o-takashi@...amocchi.jp>
---
 drivers/firewire/core-device.c           | 21 +++++++++++++++++++--
 drivers/firewire/device-attribute-test.c |  2 +-
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/drivers/firewire/core-device.c b/drivers/firewire/core-device.c
index 029ba0ff7083..829b3d590ccd 100644
--- a/drivers/firewire/core-device.c
+++ b/drivers/firewire/core-device.c
@@ -153,8 +153,25 @@ static void get_ids(const u32 *directory, int *id)

 static void get_modalias_ids(const struct fw_unit *unit, int *id)
 {
-	get_ids(&fw_parent_device(unit)->config_rom[ROOT_DIR_OFFSET], id);
-	get_ids(unit->directory, id);
+	const u32 *root_directory = &fw_parent_device(unit)->config_rom[ROOT_DIR_OFFSET];
+	const u32 *directories[] = {NULL, NULL, NULL};
+	const u32 *vendor_directory;
+	int i;
+
+	directories[0] = root_directory;
+
+	// 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)'.
+	vendor_directory = search_directory(root_directory, CSR_VENDOR);
+	if (!vendor_directory) {
+		directories[1] = unit->directory;
+	} else {
+		directories[1] = vendor_directory;
+		directories[2] = unit->directory;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(directories) && !!directories[i]; ++i)
+		get_ids(directories[i], id);
 }

 static bool match_ids(const struct ieee1394_device_id *id_table, int *id)
diff --git a/drivers/firewire/device-attribute-test.c b/drivers/firewire/device-attribute-test.c
index da2a4a09bf84..2f123c6b0a16 100644
--- a/drivers/firewire/device-attribute-test.c
+++ b/drivers/firewire/device-attribute-test.c
@@ -178,7 +178,7 @@ static void device_attr_legacy_avc(struct kunit *test)
 	};
 	struct device *node_dev = (struct device *)&node.device;
 	struct device *unit0_dev = (struct device *)&unit0.device;
-	static const int unit0_expected_ids[] = {0x00012345, 0x00000000, 0x00abcdef, 0x00543210};
+	static const int unit0_expected_ids[] = {0x00012345, 0x00fedcba, 0x00abcdef, 0x00543210};
 	char *buf = kunit_kzalloc(test, PAGE_SIZE, GFP_KERNEL);
 	int ids[4] = {0, 0, 0, 0};

-- 
2.39.2