linux-kernel - Re: [PATCH] usb bulk transfer: 1024 byte packets

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Message-ID: <9457.24.247.238.75.1176556465.squirrel@secure.gandhilinux.org>
Date:	Sat, 14 Apr 2007 09:14:25 -0400 (EDT)
From:	"Jeremy C. Andrus" <jeremy@...emya.com>
To:	linux-kernel@...r.kernel.org
Cc:	"Pete Zaitcev" <zaitcev@...hat.com>
Subject: Re: [PATCH] usb bulk transfer: 1024 byte packets

On Fri, April 13, 2007 22:16, Pete Zaitcev wrote:
>
> The transfer size in the URB is not limited by the maximum packet
> size. The HC driver splits up the transfer as specified by URB into
> the required number of packets.

The problem was not in the transfer from PC -> Device, but from Device
-> PC. If I remember correctly, the 512 limit (in the
urb->transfer_flags) is used to setup the DMA. When the device sent
packets which were 1024 bytes in size, the urb came back with a status
set to -EOVERFLOW.

The only place this could happen (in the EHCI) is in qtd_copy_status()
where the hardware has reported a "can't proceed" error (via
QTD_STS_HALT) and then the QTD_STS_BABBLE bit is set (which I interpret
to mean that the device on the other end is "babbling").

[snip]
> I presume the devices didn't show up on your doorstep with baseball
> bats to have a little chat.

In a sense they did when there was no way for me to do BULK transfers
without slamming me with 1024 byte packets :-).

        -Jeremy

-- 
-----------------------
Jeremy C. Andrus
http://www.jeremya.com/
-----------------------

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