2.3.39 ISA modem is not recognized

[Theodore Y. Ts'o]

   From: kumon en flab.fujitsu.co.jp
   Date:   Fri, 28 Jan 2000 22:22:12 +0900

   I found 2.3.39 cannot recognize my ISA supra FAX modem correctly.
   previously, I used 2.3.16 and that handle the modem without trouble.

   But when I tried to use ppp connection using 2.3.39, it produces
   following error:

   Jan 28 21:16:39 matx pppd[201]: pppd 2.3.9 started by root, uid 0
   Jan 28 21:16:39 matx kernel: LSR safety check engaged!

The "LSR safety check engaged" message means that after the interrupt
registeres are cleared in serial.c:startup(), the LSR register in the
UART is still 0xFF, which is a "should never happen situation".  It
usually means that there's no UART at that location, and so the serial
driver marks the tty as being in an error status, to avoid potentially
locking up the machine.  This explains the I/O error which chat
reported:

   Jan 28 21:16:40 matx chat[202]: Can't get terminal parameters: Input/output error

Older kernels have the same safety check, but they didn't printk a
warning.  I did that so that it would be easier to debug this situation.

I've gotten some reports that some PCMCIA modems have bad UART
emulations that have this problem, and I've had some thoughts about
adding a flag which would allow this check to by passed if a particular
modem was on an explicit "blacklist", but this is the first time I've
heard of any such problem happening with an ISA modem.  I also know why
the same modem would work under 2.3.16, but not under 2.3.39.

Can you tell me what kind of UART the Supra Fax modem has?  Also, can
you run "setserial -a /dev/ttyS1", and tell me what you find there?

						- Ted


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo en vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/