hwdb: ieee1394-unit-function: add comment about legacy AV/C devices

It appears that exceptional layout of legacy device requires extra care of
hwdb entry for node device since Linux FireWire subsystem do not pick up
numeric model identifier in vendor directory. In detail, see:

 * https://github.com/systemd/systemd/issues/25029

In the case, udev rule without model attribute is used. Thus hwdb entry
for generic AV/C device should match both cases with and without the
attribute. The wildcard added by a commit 5e577da5f824 ("hwdb: drop model
specifier from general entries") satisfies this condition,

This commit adds comment about it.

diff --git a/hwdb.d/80-ieee1394-unit-function.hwdb b/hwdb.d/80-ieee1394-unit-function.hwdb
index dcc60fd3c896ff7816c5b6af07d4ac5a5930c191..6fa1329171dff5c1f68ed7871dc9ca3e74468ac7 100644 (file)
--- a/hwdb.d/80-ieee1394-unit-function.hwdb
+++ b/hwdb.d/80-ieee1394-unit-function.hwdb
@@ -42,6 +42,11 @@
 # * Configuration ROM for AV/C Devices 1.0 (Dec. 12, 2000, 1394 Trading Association, TA Document
 #   1999027)
 #
+# Exceptional layout of configuration ROM for legacy device is described in annex of the above
+# document. The layout has some entries for model information in vendor directory instead of root
+# or unit directories. For the case, Linux FireWire subsystem don't detect Model_ID and model name,
+# thus node key without 'mo' field is detected. Wild card pattern is used to match the case with and
+# without mo field in customized key for node device.
 
 # Just for backward compatibility. Please invalidate IEEE1394_UNIT_FUNCTION_VIDEO by adding entries
 # if it is inconvenient.