From 1fe9bb4495f86700f62021cf1f048007af92483c Mon Sep 17 00:00:00 2001 From: Jiri Slaby Date: Thu, 12 Jan 2012 22:55:15 +0100 Subject: [PATCH] TTY: fix UV serial console regression commit 0eee50af5b13e00b3fb7a5fe8480419a71b8235d upstream. Commit 74c2107759d (serial: Use block_til_ready helper) and its fixup 3f582b8c110 (serial: fix termios settings in open) introduced a regression on UV systems. The serial eventually freezes while being used. It's completely unpredictable and sometimes needs a heap of traffic to happen first. To reproduce this, yast installation was used as it turned out to be pretty reliable in reproducing. Especially during installation process where one doesn't have an SSH daemon running. And no monitor as the HW is completely headless. So this was fun to find. Given the machine doesn't boot on vanilla before 2.6.36 final. (And the commits above are older.) Unless there is some bad race in the code, the hardware seems to be pretty broken. Otherwise pure MSR read should not cause such a bug, or? So to prevent the bug, revert to the old behavior. I.e. read modem status only if we really have to -- for non-CLOCAL set serials. Non-CLOCAL works on this hardware OK, I tried. See? I don't. And document that shit. Signed-off-by: Jiri Slaby References: https://lkml.org/lkml/2011/12/6/573 References: https://bugzilla.novell.com/show_bug.cgi?id=718518 Signed-off-by: Greg Kroah-Hartman --- drivers/tty/tty_port.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c index ef9dd628ba0..bf6e238146a 100644 --- a/drivers/tty/tty_port.c +++ b/drivers/tty/tty_port.c @@ -227,7 +227,6 @@ int tty_port_block_til_ready(struct tty_port *port, int do_clocal = 0, retval; unsigned long flags; DEFINE_WAIT(wait); - int cd; /* block if port is in the process of being closed */ if (tty_hung_up_p(filp) || port->flags & ASYNC_CLOSING) { @@ -284,11 +283,14 @@ int tty_port_block_til_ready(struct tty_port *port, retval = -ERESTARTSYS; break; } - /* Probe the carrier. For devices with no carrier detect this - will always return true */ - cd = tty_port_carrier_raised(port); + /* + * Probe the carrier. For devices with no carrier detect + * tty_port_carrier_raised will always return true. + * Never ask drivers if CLOCAL is set, this causes troubles + * on some hardware. + */ if (!(port->flags & ASYNC_CLOSING) && - (do_clocal || cd)) + (do_clocal || tty_port_carrier_raised(port))) break; if (signal_pending(current)) { retval = -ERESTARTSYS; -- 2.11.4.GIT