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Revert "udev: use ID_MODEL/ID_VENDOR to give friendly name for FireWire devices"

Takashi Sakamoto requested to merge takaswie/pulseaudio:topic/obsolete-fw-workaround into master

This reverts commit 3ac73598.

Systemd v249 has new entries of hwdb for node and unit in IEEE 1394 bus (hwdb.d/80-ieee1394-unit-function.hwdb). It can obsolete my workaround added by commit 3ac73598 ("udev: use ID_MODEL/ID_VENDOR to give friendly name for FireWire devices"). The hwdb entry is handy prepared. When user finds missing entry, it's preferable to file issue or merge request in systemd project site.

IEEE 1394 bus is enough legacy and it's easy to expect that few developer can evaluate the change. For reviewers, I describe the original issues and the integration of hwdb in systemd side.

In systemd, udev rule for sound card (rules.d/78-sound-card.rules) has below line to assign information in hwdb to instance for sound card.

IMPORT{builtin}="hwdb"

In the case, the udev hwdb builtin finds information according to modalias by following nodes in device topology tree toward root. For sound card associated to unit in node in IEEE 1394 bus, it's inconvenient since hwdb had no entry for the unit. The instance for node in IEEE 1394 bus doesn't have modalias. As a result, the builtin reaches 1394 OHCI controller in PCI Express bus which maintains the IEEE 1394 bus, then the value for ID_VENDOR_FROM_DATABASE and ID_MODEL_FROM_DATABASE properties from hwdb of pci device (hwdb.d/20-pci-vendor-model.hwdb) for the sound card.

For example, when two nodes are in IEEE 1394 bus and one of them has unit instance for audio and music functions, the topology of the bus is depicted in following diagram:

 * 1394 OHCI controller (pci*, modalias)
   * node A - (pci*/fw0, /dev/fw0)
   * node B - (pci*/fw1, /dev/fw1)
     * unit B-1 - (pci*/fw1/fw1.0, modalias)
       * sound card 0 - (pci*/fw1/fw1.0/sound/card0, card0)

In the case, the udev hwdb builtin picks up from hwdb of pci device for the sound card:

$ udevadm test-builtin hwdb /sys/class/sound/card2
Load module index
Parsed configuration file /usr/lib/systemd/network/99-default.link
Parsed configuration file /usr/lib/systemd/network/73-usb-net-by-mac.link
Created link configuration context.
ID_PCI_CLASS_FROM_DATABASE=Serial bus controller
ID_PCI_SUBCLASS_FROM_DATABASE=FireWire (IEEE 1394)
ID_PCI_INTERFACE_FROM_DATABASE=OHCI
ID_VENDOR_FROM_DATABASE=Texas Instruments
ID_MODEL_FROM_DATABASE=XIO2213A/B/XIO2221 IEEE-1394b OHCI Controller [Cheetah Express]
Unload module index
Unloaded link configuration context.

The aim of my workaround is to avoid using ID_VENDOR_FROM_DATABASE and ID_MODEL_FROM_DATABASE for sound card associated to unit in IEEE 1394 bus. Instead, ID_VENDOR and ID_MODEL properties are used.

However, it has another issue. For the properties, the udev rule for sound card has the other lines for sound card associated to unit in IEEE 1394 bus, below:

SUBSYSTEMS=="firewire", ATTRS{guid}=="?*", \
  ENV{ID_BUS}="firewire", ENV{ID_SERIAL}="$attr{guid}", ENV{ID_SERIAL_SHORT}="$attr{guid}", \
  ENV{ID_VENDOR_ID}="$attr{vendor}", ENV{ID_MODEL_ID}="$attr{model}", \
  ENV{ID_VENDOR}="$attr{vendor_name}", ENV{ID_MODEL}="$attr{model_name}"
SUBSYSTEMS=="firewire", GOTO="skip_pci"

The values of ID_VENDOR and ID_MODEL properties come from vendor_name and model_name attributes in parent instance of the sound card, therefore they come from audio and music units in IEEE 1394 bus. Unfortunately these attributes are not available always.

All of nodes in IEEE 1394 bus should have configuration ROM in place according to IEEE 1212 and Linux FireWire subsystem parses the content of ROM to detect units in the node. At the same time, the subsystem manages to detect information about vendor and model according to standard layout defined by 1394 Trading Association[1].

When the content of ROM is against the standard, the subsystem is discouraged the name detection. In the case, vendor_name and model_name attributes are not available, and supplemental information should be from software implementation.

The new hwdb (hwdb.d/80-ieee1394-unit-function.hwdb) added to systemd v249 can solve the above issues. The prepared names for vendor and model in hwdb are assigned to both node and unit. The udev hwdb builtin can find the vendor and model names for the unit according to modalias before arriving at pci-device. Regardless of standard or non-standard configuration ROM, the hwdb gives prepared names of vendor and model.

This is an example of Mark of the Unicorn (MOTU) Traveler. The search finishes at instance for unit in IEEE 1394 bus expectedly:

$ udevadm test-builtin hwdb /sys/class/sound/card2
Load module index
Parsed configuration file /usr/lib/systemd/network/99-default.link
Parsed configuration file /usr/lib/systemd/network/73-usb-net-by-mac.link
Created link configuration context.
ID_MODEL_FROM_DATABASE=Traveler
ID_VENDOR_FROM_DATABASE=MOTU
IEEE1394_UNIT_FUNCTION_AUDIO=1
IEEE1394_UNIT_FUNCTION_MIDI=1
Unload module index
Unloaded link configuration context.

[1] Configuration ROM for AV/C Devices 1.0 (Dec. 12, 2000, 1394 Trading Association, TA Document 1999027)

Signed-off-by: Takashi Sakamoto o-takashi@sakamocchi.jp

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