linux-kernel - Re: [PATCH] Fix data loss in cdc-acm

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Message-ID: <1437577303.5445.7.camel@suse.com>
Date:	Wed, 22 Jul 2015 17:01:43 +0200
From:	Oliver Neukum <oneukum@...e.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Johan Hovold <johan@...nel.org>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Toby Gray <toby.gray@...lvnc.com>,
	Sven Brauch <mail@...nbrauch.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-serial@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH] Fix data loss in cdc-acm

On Wed, 2015-07-22 at 10:30 -0400, Peter Hurley wrote:
> 3. Pre-allocate space _before_ the data arrives (with
> tty_buffer_request_room());
>    this is applicable to subsystems which know how much data can be
> in-flight
>    at any one time. This guarantees that when rx data arrives buffer
> space is
>    available (since it has already been allocated).
> 
> Drivers that use method 2 typically attempt to recopy the buffered
> data
> when either new data arrives or @ unthrottle. I've seen others use
> deferred
> work as well.
> 
> AFAIK no driver/subsystem is using method 3 for guaranteed delivery
> of in-flight data, but it seems ideally suited to usb serial.

Indeed. But flow control is still done by throttle/unthrottle, isn't it?

	Regards
		Oliver


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