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

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Date:	Fri, 25 Sep 2009 19:46:51 +0200
From:	Michael Trimarchi <trimarchi@...dalf.sssup.it>
To:	Johan Hovold <jhovold@...il.com>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	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.

Johan Hovold wrote:
> 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).
>   
Hi,

Using two urb, double buffering and schedule a tasklet to complete the
the reading phase. The usb will use the other free urb during receiving 
process.
I think remove tty_latency is not a good fix.

Michael
> /Johan
>
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