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

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Date:	Thu, 24 Sep 2009 23:15:00 +0200
From:	Johan Hovold <jhovold@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Oliver Neukum <oliver@...kum.org>,
	Johan Hovold <jhovold@...il.com>,
	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 Thu, Sep 24, 2009 at 08:21:07PM +0100, Alan Cox wrote:
> On Thu, 24 Sep 2009 21:03:47 +0200
> Oliver Neukum <oliver@...kum.org> wrote:

> > Am Donnerstag, 24. September 2009 17:40:23 schrieb Johan Hovold:
> > > Is there a reason why this was not fixed in ftdi_sio (and whiteheat?)
> > > along with the other drivers?

> > No good reason. They escaped my grep pattern. Mea culpa.

> ftdi_sio is correct with low_latency set as it uses a work queue to
> process the packets received.

AFAICT it only uses the work queue if tty_buffer_request_room fails to
allocate enough space. This being the exception, the completion
handler normally processes the packets in interrupt context and this is
where I get my lockdep traces (and it happens every time I hit the echo
or throttle paths).

/Johan

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