linux-kernel - Re: [patch 5/6] ps3: BD/DVD/CD-ROM Storage Driver

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Date:	Tue, 17 Jul 2007 07:38:48 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	James Bottomley <James.Bottomley@...elEye.com>,
	Arnd Bergmann <arnd@...db.de>, linux-scsi@...r.kernel.org,
	Linux Kernel Development <linux-kernel@...r.kernel.org>,
	Alessandro Rubini <rubini@...ion.unipv.it>,
	Linux/PPC Development <linuxppc-dev@...abs.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [patch 5/6] ps3: BD/DVD/CD-ROM Storage Driver

> Upon closer look, while flush_kernel_dcache_page() is a no-op on ppc64,
> flush_dcache_page() isn't. So I'd prefer to not call it if not really needed.
> 
> And according to James, flush_kernel_dcache_page() should be sufficient...
> 
> So I'm getting puzzled again...

flush_dcache_page() handles icache vs. dcache coherency by clearing the
PG_arch_1 bit in the struct page that indicates that the page is cache
clean.

You -must- call it if you're going to use any form of CPU access to
write to the page (basically dirtying the data cache) and that page can
be ever mapped into user space and executed from.

I don't know what flush_kernel_dcache_page() does and if it needs a
similar treatement, it's a new interface, so maybe Jens and or James can
tell me more about it..

Cheers,
Ben.

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