netdev - Re: [PATCH RFC 1/1] usb: Tell xhci when usb data might be misaligned

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Message-ID: <87bnytqg65.fsf@nemi.mork.no>
Date:	Thu, 30 Jan 2014 23:05:22 +0100
From:	Bjørn Mork <bjorn@...k.no>
To:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	David Laight <David.Laight@...LAB.COM>,
	"linux-usb\@vger.kernel.org" <linux-usb@...r.kernel.org>,
	"netdev\@vger.kernel.org" <netdev@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	David Miller <davem@...emloft.net>,
	Dan Williams <dan.j.williams@...el.com>,
	"Nyman\, Mathias" <mathias.nyman@...el.com>,
	Mark Lord <mlord@...ox.com>, Freddy Xin <freddy@...x.com.tw>
Subject: Re: [PATCH RFC 1/1] usb: Tell xhci when usb data might be misaligned

Sarah Sharp <sarah.a.sharp@...ux.intel.com> writes:
> On Thu, Jan 30, 2014 at 04:43:54PM -0500, Alan Stern wrote:
>
>> ehci-hcd gets along okay with the restriction that each SG element 
>> except the last has to be a multiple of the maxpacket size.  xhci-hcd 
>> can relax this quite a lot, but not all the way.
>
> What does the EHCI driver do when it receives a SG list from the USB
> networking layer that violates this restriction?

The USB networking layer won't use SG with the EHCI driver.

Commit bcc48f1a7a0d4 introduced no_sg_constraint so that usbnet could
enable SG only for host controllers with no such restrictions. I.e.
currently for xHCI only.


Bjørn
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