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

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Date:	Fri, 26 Feb 2010 11:52:07 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Catalin Marinas <catalin.marinas@....com>
cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	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 Fri, 26 Feb 2010, Catalin Marinas wrote:

> For mmap'ed pages (and present in the page cache), is it guaranteed that
> the HCD driver won't write to it once it has been mapped into user
> space? If that's the case, it may solve the problem by just reversing
> the meaning of PG_arch_1 on ARM and assume that a newly allocated page
> has dirty D-cache by default.

Nothing is guaranteed.  The HCD will write to wherever it is asked.  If 
a driver does input to an mmap'ed page, the HCD won't even know that 
the page is mmap'ed.

Alan Stern

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