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From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: David Newall <davidn@davidnewall.com>
Cc: Greg KH <greg@kroah.com>,
	linux-usb@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Handshaking on USB serial devices
Date: Thu, 14 Feb 2008 12:10:26 +0000	[thread overview]
Message-ID: <20080214121026.16a9c510@core> (raw)
In-Reply-To: <47B40918.20206@davidnewall.com>

> To make it clear: Even aside from the buffer in 2.6's pl2303.c, there's
> a race: An in-flight write URB can fill all hardware buffers, making
> unsafe what previously appeared to be a safe write.  I think it's
> essential to delay submission of the URB on a stop-transmit condition.

Hardware flow control *is* a race, and always will be. The remote end has
a delay in signalling 'stop' there is a propogation delay and a response
delay. This is why most implementations assert stop a bit *before* they
run out.

Given the size of transfers and the internal buffering one would hope the
USB devices do their own flow control if told to properly.

Alan

  reply	other threads:[~2008-02-14 12:18 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-13 14:45 David Newall
2008-02-14  5:02 ` Greg KH
2008-02-14  9:25   ` David Newall
2008-02-14 12:10     ` Alan Cox [this message]
2008-02-14 16:16       ` Gene Heskett
2008-02-14 16:31         ` Alan Cox
2008-02-14 17:55           ` Gene Heskett
2008-02-14 19:37             ` Alan Cox
2008-02-14 20:04               ` Gene Heskett
2008-02-14 20:52                 ` Greg KH
2008-02-14 21:32                   ` Gene Heskett
2008-02-15  5:08               ` David Newall
2008-02-14 22:39         ` Krzysztof Halasa
2008-02-14 23:09           ` Gene Heskett
2008-02-14 18:04       ` David Newall
2008-02-14 18:53         ` David Brownell
2008-02-14 19:36         ` Alan Cox
2008-02-21 15:22           ` David Newall
2008-02-21 15:15             ` Alan Cox
2008-02-21 19:35               ` David Newall
2008-02-21 20:58                 ` Greg KH
2008-02-14 20:47     ` Greg KH
2008-02-15  5:19       ` David Newall
2008-02-14 11:55   ` Alan Cox
     [not found] <9Wr5Z-7cw-1@gated-at.bofh.it>
     [not found] ` <9WSJ4-222-21@gated-at.bofh.it>
     [not found]   ` <9WTlN-2T0-7@gated-at.bofh.it>
     [not found]     ` <9WTYn-3Zb-29@gated-at.bofh.it>
2008-02-15 12:00       ` Bodo Eggert

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