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    SubjectRe: [PATCH] USB: ftdi_sio: Remove tty->low_latency.
    On Sat, 3 Oct 2009 13:42:29 +0200
    Johan Hovold <jhovold@gmail.com> wrote:

    > On Fri, Oct 02, 2009 at 05:33:08PM +0100, Alan Cox wrote:
    > > For upstream how does this look as a tidy up
    >
    > I found a couple of issues:
    >
    > - The patch breaks unthrottling, as it checks THROTTLE before resubmitting
    > urb whereas unthrottle checks ACTUALLY_UNTROTTLED which is never set.
    >
    > - The countread stuff should also be removed from
    > ftdi_read_bulk_callback as they where only used for updating
    > rx_bytes,
    >
    > And, obviously, this doesn't solve the problem of tty_flip_buffer_push
    > being called from interrupt context (but I assume that was never the
    > intention).

    Calling tty_flip_buffer_push from an interrupt is perfectly acceptable
    providing tty->low_latency isn't set: which it isn't.

    > I've actually been working on cleaning up ftdi_sio inspired by the
    > generic driver. I also threw out the work queue, but had not noticed the
    > unused rx_byte yet. I also used the generic drivers scheme of not
    > pushing to tty until unthrottled, but as you point out this is not really
    > needed anymore.

    The generic driver is a very bad example to follow in some areas but
    this looks a big improvement. There are some patches reworking the
    generic code to use kfifo on the output side which make it vastly better.
    Not sure where the relevant google submissions went ?

    > - spin_lock_irqsave(&priv->rx_lock, flags);
    > - priv->rx_flags &= ~(THROTTLED | ACTUALLY_THROTTLED);
    > - spin_unlock_irqrestore(&priv->rx_lock, flags);
    > + spin_lock_irqsave(&port->lock, flags);
    > + port->throttled = 0;
    > + spin_unlock_irqrestore(&port->lock, flags);

    If you only have a single bit use the set_bit/clear_bit/test_and_xxx_bit
    stuff as it's faster on most boxes

    > + * The per character mucking around with sysrq path it too slow, so
    > + * shortcircuit it in the 99.9999999% of cases where the USB serial is
    > + * not a console anyway.
    > + */
    > + ch = packet + 2;
    > + len -= 2;
    > + if (!port->console || !port->sysrq)

    You need && flag == TTY_NORMAL ?

    Definitely a move in the right direction


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