A customer has indicated they need kernel-level flow control at ttyS0 level They have enabled the following: - in the kernel command line : "console=ttyS0,115200n8r" - in /etc/inittab : "/sbin/agetty -h ttyS0 115200 vt100-nav" That apparently works fine for user level, but not kernel level. One issue appears to be that UPF_CONS_FLOW is not set in up->port.flags and so the code never enters: drivers/serial/8250.c 1631 if (up->port.flags & UPF_CONS_FLOW) { 1632 struct uart_info *info = up->port.info; 1633 unsigned int msr; 1634 1635 tmout = 1000000; 1636 while (--tmout) { 1637 msr = serial_in(up, UART_MSR); 1638 1639 if ((info->flags & UIF_CTS_FLOW) && 1640 (msr & UART_MSR_CTS)) 1641 break; 1642 else if ((info->flags & UIF_DSR_FLOW) && 1643 (msr & UART_MSR_DSR)) 1644 break; 1645 1646 udelay(1); 1647 touch_nmi_watchdog(); 1648 } 1649 } 1650 } The howto indicates issues that need to be resolved: http://www.faqs.org/docs/Linux-HOWTO/Remote-Serial-Console-HOWTO.html#BUGS-KERNELP I believe the patch mentioned is http://lkml.indiana.edu/hypermail/linux/kernel/0310.2/1080.html but it is old and not in 2.6.33 and I find no sign offs or commits. It doesn't apply cleanly to rhel5. I'm hoping somebody more knowledgeable in this can look at this issue and see what needs to be done to enable kernel-level flow control.
Pierre, It occurred to me that I din't ask a basic question about this BZ: for RTS/CTS flow control to work, the customer needs to have a properly wired cable. There are several ways to wire serial cables, as shown, for example, at: http://www.lammertbies.nl/comm/info/RS-232_null_modem.html A 3-wire cable won't offer hardware level flow control. There are even some ways of wiring the cable that will fake hardware control to the serial interfaces (like the "Null modem with loop back handshaking" wiring schema showed on the above site). With those cables, if the serial application is programmed to use RTS/CTS, it will work, but flow control will fail if needed, as it is not properly wired. So, the question is: how are their console cables wired?
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