Per IEEE 1394 clause 8.4.2.3, a contender for the IRM role shall check
whether the current IRM complies to 1394a-2000 or later. If not force a
compliant node (e.g. itself) to become IRM. This was implemented in the
older ieee1394 driver but not yet in firewire-core.
An older Sony camcorder (Sony DCR-TRV25) which implements 1394-1995 IRM
but neither 1394a-2000 IRM nor BM was now found to cause an
interoperability bug:
- Camcorder becomes root node when plugged in, hence gets IRM role.
- firewire-core successfully contends for BM role, proceeds to perform
gap count optimization and resets the bus.
- Sony camcorder ignores presence of a BM (against the spec, this is
a firmware bug), performs its idea of gap count optimization and
resets the bus.
- Preceding two steps are repeated endlessly, bus never settles,
regular I/O is practically impossible.
http://thread.gmane.org/gmane.linux.kernel.firewire.user/3913
This is an interoperability regression from the old to the new drivers.
Fix it indirectly by adding the 1394a IRM check. The spec suggests
three and a half methods to determine 1394a compliance of a remote IRM;
we choose the method of testing the Config_ROM.Bus_Info.generation
field. This is data that firewire-core should have readily available at
this point, i.e. does not require extra I/O.
Reported-by: Clemens Ladisch <clemens@ladisch.de> (missing 1394a check)
Reported-by: H. S. <hs.samix@gmail.com> (issue with Sony DCR-TRV25)
Tested-by: H. S. <hs.samix@gmail.com>
Cc: <stable@kernel.org> # .32.x and newer
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
1038953674