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

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Message-ID: <1267220163.23523.1806.camel@pasglop>
Date:	Sat, 27 Feb 2010 08:36:03 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	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, 2010-02-26 at 16:00 +0000, Catalin Marinas wrote:
> > I'm surprised that usb-storage has an issue here. It shouldn't
> afaik,
> > since it's just a SCSI driver (or not anymore ?) and the BIO or
> > filesystems handle things there no ? I haven't seen a single call to
> > flush_dcache_page() in any of drivers/scsi, drivers/ata or
> drivers/ide
> > when I looked...
> 
> The BIO or filesystem code don't call flush_dcache_page() either (well
> some do like cramfs or jffs but they decompress the data received from
> the block device). 

That's weird... that would mean that all existing PIO IDE or SCSI is
broken etc... Including I$/D$ cache coherency on powerpc and more. That
surprises me :-)

On an older kernel tree here:

$ grep -r flush_dcache_page fs | wc -l
118

So maybe that's where things need fixing ?

Cheers,
Ben.




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