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SubjectRe: [PATCH] USB: ftdi_sio: Remove tty->low_latency.
On Sat, Oct 03, 2009 at 02:18:07PM +0100, Alan Cox wrote:
> 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:
> > 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.

Of course -- the "with low latency set" part fell out (or, was implicit
;-) ). Your patch, however, still has low_latency set when it calls
tty_flip_buffer_push and that's the problem.

> > - 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 generic driver uses two fields in usb_serial_port for
throttled/trottle_req, whereas ftdi_sio, whiteheat, aircable, cypress
and perhaps a couple more have private a flag field for THROTTLED and
ACTUALLY_THROTTLED.

How about unifying them to all use a single flag field (with two flags)
in usb_serial_port?

> > + * 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 ?

You tell me. :-) Are we interested in them unless port->console is set?

> Definitely a move in the right direction

Thanks,
Johan



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