netdev - RE: [PATCH] usb: xhci: Link TRB must not occur with a USB payload burst.

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Message-ID: <AE90C24D6B3A694183C094C60CF0A2F6026B743D@saturn3.aculab.com>
Date:	Wed, 20 Nov 2013 17:16:12 -0000
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Sarah Sharp" <sarah.a.sharp@...ux.intel.com>
Cc:	"Alan Stern" <stern@...land.harvard.edu>,
	"Ben Hutchings" <bhutchings@...arflare.com>,
	<netdev@...r.kernel.org>, <linux-usb@...r.kernel.org>
Subject: RE: [PATCH] usb: xhci: Link TRB must not occur with a USB payload burst.

> Ok, so the networking layer should be fine.  However, with the current
> patch, if the mass storage driver sends down a scatter-gather list
> that's bigger than a ring segment, or needs to be split up so it doesn't
> cross 64K boundaries, then the URB submission will fail.  We don't want
> that to happen.

My suspicion is that long SG lists are unusual - otherwise the
ring expansion code would have been needed much earlier.

Can anyone remember whether that was needed because of long SG lists
or because of large numbers of outstanding requests?

I've seen it for network cards - but only because usbnet sends
down far too many tx buffers.

	David



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