ufdti issues - compile kernel without module

[Bram Van Steenlandt]

Hi,

I'm porting a plc/automation system from linux to freebsd and while 
doing so I've discovered some issues with uftdi (the system use a couple 
of rs485 connections).

Under linux I'v used the ftdi adapters as com ports, they show up as 
/dev/ttyUSB0 etc, this works mostly ok.
With freebsd, I've found that while ufdti works it's much slower than 
it's linux counterpart,
with linux the Tx/Rx leds are flashing rapidly, I can poll a plc 10 
times per second, with freebsd this was about 2 times per second, serial 
parameters are the same.
I've found other reports online from people who experience similar issues.

I then tried porting the application so that it uses libftdi (in serial 
mode), when using libftdi performance was very good also on freebsd.
So the problem must be the uftdi kernel module (I think).

You can't use libftdi if you have the uftdi kernel module loaded.
I did not succeed in building a kernel without the uftdi module, 
deleting it from /boot/kernel works but probably isn't "the way".

I've tried:
to put
WITHOUT_MODULES=uftdi
in /etc/make.conf
but this makes no difference, when running make buildkernel it still 
build the module.

Is there a way to do this ?
Or does freebsd have it's own blacklist system ?
I've found various information online and I've tried various things but 
I can't seem to get this to work.

thx
Bram