linux-kernel - Re: [PATCH] USB: ftdi_sio: Remove tty->low

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Date:	Wed, 30 Sep 2009 11:05:41 +0200
From:	Johan Hovold <jhovold@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Johan Hovold <jhovold@...il.com>,
	Michael Trimarchi <trimarchi@...dalf.sssup.it>,
	Oliver Neukum <oliver@...kum.org>,
	Greg Kroah-Hartman <gregkh@...e.de>, linux-usb@...r.kernel.org,
	Alan Cox <alan@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: ftdi_sio: Remove tty->low_latency.

On Tue, Sep 29, 2009 at 11:52:32PM +0100, Alan Cox wrote:
> > As it stands today ftdi_sio does indeed call tty_flip_buffer_push from
> > interrupt context with low_latency set and that is obviously incorrect,
> > right?
> 
> It seems to do it from a work queue - or did I miss a case ?

The function used for deferred work is actually called directly from
ftdi_read_bulk_callback: 

  ftdi_process_read(&priv->rx_work.work);

It only gets scheduled on the work queue when unthrottled (or if
tty_buffer_request_room(tty, length) < length before serial_throttle is
called).

So basically, unless throttled, it is always called from interrupt
context.

/Johan

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