linux/drivers/firewire
Clemens Ladisch 7f51a100bb firewire: ohci: retransmit isochronous transmit packets on cycle loss
In isochronous transmit DMA descriptors, link the skip address pointer
back to the descriptor itself.  When a cycle is lost, the controller
will send the packet in the next cycle, instead of terminating the
entire DMA program.

There are two reasons for this:

* This behaviour is compatible with the old IEEE1394 stack.  Old
  applications would not expect the DMA program to stop in this case.

* Since the OHCI driver does not report any uncompleted packets, the
  context would stop silently; clients would not have any chance to
  detect and handle this error without a watchdog timer.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

Pieter Palmers notes:

"The reason I added this retry behavior to the old stack is because some
cards now and then fail to send a packet (e.g. the o2micro card in my
dell laptop).  I couldn't figure out why exactly this happens, my best
guess is that the card cannot fetch the payload data on time.  This
happens much more frequently when sending large packets, which leads me
to suspect that there are some contention issues with the DMA that fills
the transmit FIFO.

In the old stack it was a pretty critical issue as it resulted in a
freeze of the userspace application.

The omission of a packet doesn't necessarily have to be an issue.  E.g.
in IEC61883 streams the DBC field can be used to detect discontinuities
in the stream.  So as long as the other side doesn't bail when no
[packet] is present in a cycle, there is not really a problem.

I'm not convinced though that retrying is the proper solution, but it is
simple and effective for what it had to do.  And I think there are no
reasons not to do it this way.  Userspace can still detect this by
checking the cycle the descriptor was sent in."

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de> (changelog, comment)
2010-02-14 15:10:41 +01:00
..
core-card.c firewire: core: add_descriptor size check 2010-01-26 20:54:50 +01:00
core-cdev.c firewire: core: fix use-after-free regression in FCP handler 2010-01-26 20:54:50 +01:00
core-device.c driver model: constify attribute groups 2009-09-15 09:50:47 -07:00
core-iso.c firewire: core: fix crash in iso resource management 2009-09-05 15:59:34 +02:00
core-topology.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/trivial 2009-12-09 19:43:33 -08:00
core-transaction.c firewire: fix use of multiple AV/C devices, allow multiple FCP listeners 2009-12-29 19:58:16 +01:00
core.h firewire: core: optimize Topology Map creation 2009-10-14 23:10:48 +02:00
Kconfig firewire, ieee1394: update Kconfig help 2009-12-29 19:58:17 +01:00
Makefile firewire: net: add Kconfig item, rename driver 2009-06-14 14:26:29 +02:00
net.c firewire: net: fix panic in fwnet_write_complete 2010-02-01 21:51:28 +01:00
ohci.c firewire: ohci: retransmit isochronous transmit packets on cycle loss 2010-02-14 15:10:41 +01:00
ohci.h firewire: reorganize header files 2009-06-05 16:26:18 +02:00
sbp2.c firewire: normalize style of queue_work wrappers 2009-10-14 23:10:48 +02:00