From: Jiri Slaby <jslaby@xxxxxxx> 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 <jslaby@xxxxxxx> Cc: stable <stable@xxxxxxxxxxxxxxx> 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 <gregkh@xxxxxxx> --- drivers/tty/tty_port.c | 12 +++++++----- 1 files changed, 7 insertions(+), 5 deletions(-) diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c index ef9dd62..bf6e238 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; -- 1.7.8.3 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
