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

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Date:	Wed, 03 Mar 2010 10:26:56 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	James.Bottomley@...senPartnership.com, linux@....linux.org.uk,
	catalin.marinas@....com, mdharm-kernel@...-eyed-alien.net,
	linux-usb@...r.kernel.org, x0082077@...com,
	sshtylyov@...mvista.com, tom.leiming@...il.com,
	bigeasy@...utronix.de, oliver@...kum.org,
	linux-kernel@...r.kernel.org, santosh.shilimkar@...com,
	pavel@....cz, greg@...ah.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: USB mass storage and ARM cache coherency

On Tue, 2010-03-02 at 21:11 +0900, FUJITA Tomonori wrote:
> 
> > Sorry to be a bit late to the party (on holiday), but I/D coherency
> is
> > supposed to be taken care of using flush_cache_page in the memory
> > mapping routines.
> 
> powerpc does that? To be exact, powerpc doesn't need
> flush_cache_page() and handles I/D coherency in the pte modification
> code. powerpc uses PG_arch_1 to avoid unnecessarily handling I/D
> coherency. Seems that IA64 does the same trick with PG_arch_1.

Right. We set PG_arch_1 to avoid doing it again of a given physical
page. We assume that it's always cleared when a page is recycled by the
page cache and we also clear it in flush_dcache_page() though the need
for that later thing is dubious...

Cheers,
Ben.


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