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

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Message-ID: <Pine.LNX.4.44L0.1311201121350.1826-100000@iolanthe.rowland.org>
Date:	Wed, 20 Nov 2013 11:26:52 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	David Laight <David.Laight@...LAB.COM>
cc:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	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.

On Wed, 20 Nov 2013, David Laight wrote:

> > From: Sarah Sharp
> ...
> > (Also, usb-storage aligns the block sizes to 512K, which explains why
> > we've never had an issue with TD fragments with that driver.)
> 
> What is a 'block' in that context?

I think Sarah means that usb-storage requires the block layer to align 
its data buffers to 512-byte boundaries.  (Note: 512 bytes, not 512K.)  
Disk I/O naturally tends to be done in units of the page size, anyway, 
although raw I/O can involve single sectors.

If a user supplies an unaligned buffer, the block layer will set up a 
bounce buffer.

Alan Stern

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