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    SubjectRe: UV serial regression since 2.6.36
    On 12/06/2011 11:34 PM, Jiri Slaby wrote:
    > Hi,
    > In short, the issue causes serial port traffic to stop after some time
    > on UV machines. Only when serial is used as a console. It worked
    > perfectly with 2.6.32. It's a standard 16550 on 0x3f8 (well, it's
    > emulated to be at that port). Also in the PNP subsys.
    > To reproduce that 'debug' kernel parameter must not be used.
    > The root cause seems to be that the serial "chip" there has problems
    > with interrupts. It generates some but doesn't indicate it's the source
    > or somebody clears it (NOINT is set). And when it is supposed to
    > generate one (on THRE), it does not. So there are bytes in the TX buffer
    > which are never sent. Until the port is kicked e.g. by "echo h >
    > /proc/sysrq-trigger".
    > The unhandled interrupts were always an issue, but somehow hidden. It
    > became a real problem with patches post 2.6.32.
    > I bisected it to these two commits _together_:
    > commit 3f582b8c11014e4ce310d9839fb335164195333f
    > Author: Arnd Bergmann <>
    > Date: Tue Jun 29 22:31:40 2010 +0200
    > serial: fix termios settings in open
    > AND
    > commit 74c2107759dc6efaa1b9127014be58a742a1e7ac
    > Author: Alan Cox <>
    > Date: Tue Jun 1 22:53:00 2010 +0200
    > serial: Use block_til_ready helper
    > Those reverted on the top of 2.6.37 makes it work again. Those reverted
    > on the top of 3.0 plus mine 3 reverted which removed update_set_termios
    > completely makes it work again.
    > I didn't look closely to why those patches are causing that. Like
    > c_cflag copy in uart_update_termios and "tty->termios->c_cflag & CBAUD"
    > test in tty_port_block_til_ready don't look good to me...

    My vacation is over. I suppose you haven't had a chance to take a look
    into the regression? (Just in case any of you is looking into that right
    now to not duplicate the effort.)

    > thanks,
    suse labs

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