netdev - Re: usbnet transmit path problems

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Date:	Wed, 11 Sep 2013 12:11:52 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	netdev@...r.kernel.org, Ming Lei <ming.lei@...onical.com>
Subject: Re: usbnet transmit path problems

On Wed, 2013-09-11 at 10:10 +0100, David Laight wrote:
> I've been looking at the code in drivers/net/usb/usbnet.c that
> processes tx data after the tx_fixup() function has run.
> 
> The code currently looks like:

> 1) I can't see where skb_linearize() gets called if 'can_dma_sg' is unset.

That is the job of subdrivers.

> 2) If 'length % dev->maxpacket == 0' for a multi-fragment packet then
>    the extra byte isn't added correctly (the code probably falls off
>    the end of the scatter-gather list).

Indeed. Ming Lei, should usbnet handle this in the sg case or better
leave it to the subdriver you introduced this for?

> 4) I read that USB3 has a different scheme for terminating bulk data
>    that is a multiple of the packet size.
>    Does this mean that the pad byte isn't needed for USB3?
>    (Or are USB3 controllers/targets just as buggy?)

We don't have enough examples to tell.

	Regards
		Oliver


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