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    SubjectRe: [RFC][PATCH 7/7] serial, 8250: Mostly avoid wakeups from under port->lock
    On Wed, 21 Dec 2011 11:57:46 +0100
    Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

    > While not a strict requirement (anymore), it is nice not to issue
    > wakeups (or have them connected by locks) from console output.
    >
    > This patch avoids doing most wakeups from under port->lock, which is
    > connected to 8250console_write(). Only seriously challenged UARTs will
    > still do the wakeup, but since I don't actually have such a creature,
    > I'm less inclined to fix it up.

    Gak..

    > + BUG_ON(!state);
    > + tty = state->port.tty;
    > + tty_kref_get(tty);
    > + spin_unlock_irqrestore(&up->port.lock, flags);
    > + tty_wakeup(tty);
    > + tty_kref_put(tty);

    driver innards shouldn't know this stuff and this makes it worse rather
    than cleaning it up

    The basic idea looks fine but I really don't want magic lock hackery in
    the 8250 driver. We need a way of generalising this so the code is
    cleaner and the locking internal knowledge stays out of the driver itself.

    Also I think it's probably buggy - sending the x_char is forward progress
    so probably needs to cause a wakeup.

    So for the moment NAK, but worthy of figuring out how to do it right


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