DragonFly kernel List (threaded) for 2008-01
tty(4) buffer sizes
I have tested briefly some UMTS/HSDPA modems with idea to obtain one, but
couldn't get them work reliably in DragonFly. All of them were using the
umsm(4) driver and using HSDPA (3.6Mbit/s).
The problem is that tty(4) buffers are too small. With current code I
couldn't get single MTU size packets through, dmesg was full of "kernel:
ucom0: lost 374 chars" messages. Devices started to work for me without
the messages if I increased umsm(4) buffers (UMSMBUFSZ) to 4096 and
applied this oneliner to the sys/kern/tty.c:
@@ -2307,7 +2307,7 @@ ttsetwater(struct tty *tp)
* sizes and watermarks.
cps = TTYHOG - 2 * 256;
- tp->t_ififosize = 2 * 256;
+ tp->t_ififosize = 2 * 2048;
cps = tp->t_ispeedwat / 10;
I'm not familiar with tty(4) code in general, so I'm not able to evaluate
whether it's safe or not and what other things should be changed etc.
Comment seems to say that it should apply to old devices only, but
clearly ucom(4) doesn't know anything about t_ispeedwat. Should it?
umsm(4) doesn't know anything of line speed either :). How should I
Note, that I'm not able to test every idea yet, I don't have any device
myself, but it will change soon.
As as sidenote, I think that we should rename umsm(4) to ugensa(4) like it
is NetBSD. There is nothing Qualcomm MSM chip specific in the driver.