Bug with 2.6 serial driver when in UART 8250 mode

Hello everybody,

For communicating with a serial device of ours we need to disable the UART buffer (the device at the other end doesn't have a serial buffer at all and therefore we can't use hardware control flow efficiently). The only way to do this with Linux seems to pass the UART in 8250 mode, which doesn't use the buffer:

# setserial /dev/ttyS0 uart 8250

We did that with success with 2.4 kernel series. Since most of our machines are using 2.6, we tried to do the same on them, but noticed something wrong: only one byte upon 16 is being sent. For instance, if I

$ echo -n "qwertyuiopasdfgh" > /dev/ttyS0

My device only receives the 'h', while with a 2.4 kernel it receives the entire string.

So I think that for some reason, the UART buffer is not deactivated while switching it to 8250 mode, and that the driver only sends the last byte it contains when the interrupt is triggered.

I've tried to look at the code but unfortunately only lost myself without being able to even identify the right source file to look at. Sorry about that. :/

Could someone have a look at this or point me to the right section of code so I do it myself?

Thanks,
Alex.
PS: please CC replies as I'm not subscribed to the list.

Alexandre Courbot
PhD Student - LIFL/RD2P
http://www.lifl.fr/~courbot/