I have two patches that make some changes for 78-sound-card.rules that I believe improves things: http://lists.freedesktop.org/archives/systemd-devel/2015-April/030543.html http://lists.freedesktop.org/archives/systemd-devel/2015-April/030544.html The first one changes ID_ID for USB devices to not include the ALSA "id" sysattr, which is not unique to the hardware. (This means that devices might have different ID_ID strings depending on when it was enumerated.) The second one adds firewire properties that match USB properties.
This has been merged as http://cgit.freedesktop.org/systemd/systemd/commit/?id=0414af1dfe http://cgit.freedesktop.org/systemd/systemd/commit/?id=5c0b72de3a
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