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    SubjectRe: Serial-Core: USB-Serial port current issues.
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    On Mon, 2006-06-26 at 15:26 -0700, Greg KH wrote:
    > On Fri, Jun 23, 2006 at 02:28:42PM -0300, Luiz Fernando N. Capitulino wrote:
    > > On Thu, 22 Jun 2006 09:29:40 +0100
    > > Russell King <rmk+lkml@arm.linux.org.uk> wrote:
    > >
    > > |
    > > | Consider this scenario with what you're proposing:
    > > |
    > > | thread irq
    > > |
    > > | take mutex
    > > | get_mctrl
    > > | cts changes state
    > > | take port lock
    > > | mctrl state read
    > > | tty->hw_stopped changed state
    > > | release port lock
    > > | releaes mutex
    > > | take port lock
    > > | update tty->hw_stopped
    > > | release port lock
    > > |
    > > | Now, tty->hw_stopped does not reflect the hardware state, which will be
    > > | buggy and can cause a loss of transmission.
    > > |
    > > | I'm not sure what to suggest on this one since for USB drivers you do
    > > | need to be able to sleep in this method... but for UARTs you must not.

    What about this ugly fragment?
    (assuming get_mctrl not called from IRQ)

    take mutex
    take port lock
    again:
    save local copy of icount
    release port lock
    get_mctrl
    take port lock
    if (icount changed)
    goto again
    update tty->hw_stopped
    release port lock
    release mutex

    --
    Paul





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