linux-kernel - Re: [RFC] Align tegra-ehci DMA transfers to 32B

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Message-ID: <20101217230702.GA21147@suse.de>
Date:	Fri, 17 Dec 2010 15:07:02 -0800
From:	Greg KH <gregkh@...e.de>
To:	rmorell@...dia.com
Cc:	David Brownell <dbrownell@...rs.sourceforge.net>,
	Benoit Goby <benoit@...roid.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Ming Lei <tom.leiming@...il.com>,
	Jacob Pan <jacob.jun.pan@...el.com>,
	Olof Johansson <olof@...om.net>,
	Erik Gilling <konkers@...roid.com>,
	Colin Cross <ccross@...roid.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] Align tegra-ehci DMA transfers to 32B

On Fri, Dec 17, 2010 at 02:44:29PM -0800, rmorell@...dia.com wrote:
> On Fri, Dec 17, 2010 at 02:32:27PM -0800, Greg KH wrote:
> > On Fri, Dec 17, 2010 at 01:58:47PM -0800, Robert Morell wrote:
> > > This small set of patches fixes an issue where DMA from the tegra EHCI
> > > controller could be corrupted.  It was most commonly seen with USB network
> > > adapters, though in theory it could happen with any USB traffic.
> > > 
> > > (Note: An attempt was made to fix this with commit 367c3aab, which set
> > > NET_IP_ALIGN to 0 and NET_SKB_PAD to 32.  Unfortunately, not all network
> > > drivers honor them (presumably since these are intended as optimizations rather
> > > than hard rules).  This does mean that properly-written network drivers should
> > > fall through this code with very little overhead, however.)
> > 
> > We don't have many USB network drivers, why not just fix them up to
> > handle this properly, then you will not need to change any core USB
> > code, right?
> 
> The USB core code is used by devices other than USB adapters.  We've
> only seen this problem so far with usbnet devices, but I can't test
> every USB device ever to make sure that they always align their DMA to
> 32 bytes.

Then it might just be easier for your driver to throw up a huge
WARN_ON() if it detects such memory so that the device driver could be
fixed, right?

thanks,

greg k-h
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