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From: Oliver Neukum <oliver@neukum.org>
To: Johan Hovold <jhovold@gmail.com>
Subject: Re: [PATCH] USB: ftdi_sio: Remove tty->low_latency.
Date: Sat, 3 Oct 2009 14:11:40 +0200
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Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>,
       "Eric W. Biederman" <ebiederm@xmission.com>,
       "Greg Kroah-Hartman" <gregkh@suse.de>,
       Michael Trimarchi <trimarchi@gandalf.sssup.it>,
       linux-usb@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
       linux-kernel@vger.kernel.org
References: <20090924154023.GA27480@localhost> <20091002173308.6158d734@lxorguk.ukuu.org.uk> <20091003114229.GB605@localhost>
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Am Samstag, 3. Oktober 2009 13:42:29 schrieb Johan Hovold:
> +       spin_lock_irqsave(&port->lock, flags);
> +       if (!port->throttled) {
> +               spin_unlock_irqrestore(&port->lock, flags);
> +               ftdi_submit_read_urb(port, GFP_ATOMIC);
> +       } else
> +               spin_unlock_irqrestore(&port->lock, flags);
> +}
>  
>  static void ftdi_break_ctl(struct tty_struct *tty, int break_state)
>  {
> @@ -2605,33 +2467,30 @@ static int ftdi_ioctl(struct tty_struct *tty,
> struct file *file, static void ftdi_throttle(struct tty_struct *tty)
[..]
> +       spin_lock_irqsave(&port->lock, flags);
> +       port->throttled = 1;
> +       spin_unlock_irqrestore(&port->lock, flags);
>  }
>  
> -
> -static void ftdi_unthrottle(struct tty_struct *tty)
> +void ftdi_unthrottle(struct tty_struct *tty)
[..]
> +       spin_lock_irqsave(&port->lock, flags);
> +       was_throttled = port->throttled;
> +       port->throttled = 0;
> +       spin_unlock_irqrestore(&port->lock, flags);
>  
> -       if (actually_throttled)
> -               schedule_delayed_work(&priv->rx_work, 0);
> +       if (was_throttled && !test_bit(ASYNCB_CLOSING, &port->port.flags))
> +               ftdi_submit_read_urb(port, GFP_KERNEL);
>  }

This unfortunately is incorrect. If an unthrottling happens before the read
callback runs you submit a running URB.

	Regards
		Oliver