linux-kernel - Re: [PATCH 2/2] USB: ehci: tegra: Align DMA transfers to 32 bytes

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Message-ID: <20101217235050.GK25105@morell.nvidia.com>
Date:	Fri, 17 Dec 2010 15:50:50 -0800
From:	rmorell@...dia.com
To:	Greg KH <gregkh@...e.de>
Cc:	Oliver Neukum <oliver@...kum.org>,
	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: [PATCH 2/2] USB: ehci: tegra: Align DMA transfers to 32 bytes

On Fri, Dec 17, 2010 at 03:35:27PM -0800, Greg KH wrote:
> On Sat, Dec 18, 2010 at 12:17:40AM +0100, Oliver Neukum wrote:
> > Am Samstag, 18. Dezember 2010, 00:09:40 schrieb Greg KH:
> > > I still don't like it, it feels like a hack that is not going to be able
> > > to be maintained very well.
> > > 
> > > And I still think the individual drivers should be fixed...
> > > 
> > 
> > But they are not buggy. The USB API was written under the
> > assumption that HCDs can deal with byte level granularity and alignment.
> > Hence the network driver pass DMA-able memory with an alignment
> > that suits them.
> 
> Ok, fair enough.
> 
> But I still don't like that urb flag stuff as a solution to this...

Yeah, I wish I knew of a better way to store this information.
urb->hcpriv seems like a nice place for host controller-private data,
but it's used by the general ehci framework throughout the lifetime of
an URB so isn't suitable for this case.

Thanks,
Robert

> thanks,
> 
> greg k-h
> 
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