linux-kernel - Re: USB mass storage and ARM cache coherency

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Date:	Wed, 24 Feb 2010 11:19:28 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
cc:	Catalin Marinas <catalin.marinas@....com>,
	Matthew Dharm <mdharm-kernel@...-eyed-alien.net>,
	<linux-usb@...r.kernel.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	"Mankad,Maulik Ojas" <x0082077@...com>,
	Sergei Shtylyov <sshtylyov@...mvista.com>,
	Ming Lei <tom.leiming@...il.com>,
	Sebastian Siewior <bigeasy@...utronix.de>,
	Oliver Neukum <oliver@...kum.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Shilimkar,Santosh" <santosh.shilimkar@...com>,
	Pavel Machek <pavel@....cz>, Greg KH <greg@...ah.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	James Bottomley <James.Bottomley@...senPartnership.com>
Subject: Re: USB mass storage and ARM cache coherency

On Wed, 24 Feb 2010, Benjamin Herrenschmidt wrote:

> > The PIO HCD drivers, however, don't call flush_dcache_page(). Is it possible
> > that the HCD could transfer data into a page cache page already mapped
> > in user space? My understanding is that the scenario above is possible.
> 
> It is but I'm not confident the responsibility for doing that cleanup
> is at the HCD level. That would impact a lot of HCD activities that
> don't need such flushing since the use of the page is purely in-kernel.

That's right.  The HCD merely puts data wherever it's told to.  It 
doesn't know whether the destination is in the page cache, in 
userspace, or anywhere else.  The same is true for usb-storage.

Alan Stern

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