On 04/27/2012 07:42 PM, Benjamin Herrenschmidt wrote:

Ok, so you do have a serial port, probably two even :-) One of them is
connected to the infra red transceiver and the other one is probably
connected to the internal modem.

(The modem itself might not use it, some of these machines use an
i2s/i2c modem, some use a usb modem, but the serial port is wired to the
connector regardless).

I have done a little more debugging. The problem is definitely coming from 
drivers/tty/serial/pmac_zilog.c. I am getting ChanB interrupts while open, which 
causes the following code segment to return IRQ_NONE:

        if (r3 & (CHBEXT | CHBTxIP | CHBRxIP)) {
                if (!ZS_IS_OPEN(uap_a)) {
                        pmz_debug("ChanB interrupt while open !\n");
                        goto skip_b;
                }
                write_zsreg(uap_b, R0, RES_H_IUS);
                zssync(uap_b);
                if (r3 & CHBEXT)

When this section is entered, r3 == 0x2 (CHBTxIP).

Larry