staging: Add firewire-serial driver

v2 of this driver submission builds and runs cleanly against Greg KH's tty-next and (hopefully) addresses the concerns raised regarding the dependence on tty_buffer internals; specifically with the workarounds to fix
1) data loss on hangup and 2) throttling before the flip buffers are full.

1) Data loss on hangup
Although I experimented with alternative solutions as Alan suggested, none were practical. For example, this sequence (which is almost identical to what the n_tty ldisc does in input_available_p()):

     tty_flush_to_ldisc(tty);
     n = ldisc->ops->chars_in_buffer(tty);

suffers from a race that the ldisc could have _just_ emptied the read buffer between these calls, so that n == 0 but data is still in the flip buffers.

For now, the driver v2 delays the hangup on carrier loss by a fixed timeout.

2) Flip buffers full before throttle received from ldisc Because driver throttling is performed by the ldisc, and not by the tty_buffer, the flip buffers can be filled before receiving a throttle request.

For now, the driver v2 pre-buffers in front of the tty_buffer; ie, rx data which is not accepted by tty_insert_flip_string...() is buffered in the driver, the sender is throttled and when ldisc unthrottles, normal operation resumes by feeding the tty_buffer from the pre-buffered data.

This driver v2 also fixes the occasionally flaky auto-connect, 2 (valid) lockdep warnings, racy line status changes, and delays fifo allocation until .activate() to minimize memory footprint.

As before, the TODO file notes the remaining issues.

Regards,
Peter

Peter Hurley (1):
staging: fwserial: Add TTY-over-Firewire serial driver

 drivers/staging/Kconfig             |    2 +
 drivers/staging/Makefile            |    1 +
 drivers/staging/fwserial/Kconfig    |    9 +
 drivers/staging/fwserial/Makefile   |    2 +
 drivers/staging/fwserial/TODO       |   37 +
 drivers/staging/fwserial/dma_fifo.c |  310 ++++
 drivers/staging/fwserial/dma_fifo.h |  130 ++
 drivers/staging/fwserial/fwserial.c | 2946 +++++++++++++++++++++++++++++++++++
 drivers/staging/fwserial/fwserial.h |  387 +++++
 9 files changed, 3824 insertions(+)
 create mode 100644 drivers/staging/fwserial/Kconfig
 create mode 100644 drivers/staging/fwserial/Makefile
 create mode 100644 drivers/staging/fwserial/TODO
 create mode 100644 drivers/staging/fwserial/dma_fifo.c
 create mode 100644 drivers/staging/fwserial/dma_fifo.h
 create mode 100644 drivers/staging/fwserial/fwserial.c
 create mode 100644 drivers/staging/fwserial/fwserial.h

1.7.12.3