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

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Date:	Fri, 02 Oct 2009 15:29:56 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Johan Hovold <jhovold@...il.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Michael Trimarchi <trimarchi@...dalf.sssup.it>,
	Oliver Neukum <oliver@...kum.org>, 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.

Alan Cox <alan@...rguk.ukuu.org.uk> writes:

>> Alan, did you have time to look at it? Are there any reasons for wanting
>> to keep low_latency in ftdi_sio when it was removed from all other
>> drivers processing in interrupt context (without doing work queue
>> re-implementations)?
>
> Yes for latency handling (two layers of work queue is bad) but its the
> right fix for stable.
>
> For upstream how does this look as a tidy up
> ftdi_sio: simplify driver
>
> From: Alan Cox <alan@...ux.intel.com>
>
> This does a lot of stuff that the modern buffering logic will cover itself
> so remove the cruft.
>
> - Remove the code handling throttle half way through a packet. We have 64K
>   of slack and flow control is async anyway so stopping is the wrong thing
>   to do
> - Remove various commented out bits
> - Without the partial packet stuff we can remove the async queue stuff and
>   split it into sensible functions for URB processing and for queueing urbs
>   for receipt
> - Remove the unused rx_bytes count. We take locks for it, we jump through
>   hoops for it and we never expose it.
>
> Signed-off-by: Alan Cox <alan@...ux.intel.com>

The code doesn't fall over immediately in my testing.  So at first glance
this appears to be as good as removing low_latency.

Eric

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