linux-kernel - Re: [PATCH] isp1760: Flush the D-cache for the pipe-in transfer buffers

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Message-Id: <1265124519.12634.80.camel@pc1117.cambridge.arm.com>
Date:	Tue, 02 Feb 2010 15:28:39 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	Greg KH <greg@...ah.com>,
	Matthew Dharm <mdharm-kernel@...-eyed-alien.net>
Subject: Re: [PATCH] isp1760: Flush the D-cache for the pipe-in transfer
	buffers

On Tue, 2010-02-02 at 12:08 +0000, Sebastian Andrzej Siewior wrote:
> * Catalin Marinas | 2010-02-02 11:11:35 [+0000]:
> 
> >When the HDC driver writes the data to the transfer buffers it pollutes
> >the D-cache (unlike DMA drivers where the device writes the data). If
> >the corresponding pages get mapped into user space, there are no
> >additional cache flushing operations performed and this causes random
> >user space faults on architectures with separate I and D caches
> >(Harvard) or those with aliasing D-cache.
> 
> After looking through lib/scatterlist.c it uses
> #include <linux/highmem.h>
> 
> and
> 
> flush_kernel_dcache_page().
> Wouldn't this do the job here as well?

The documentation implies that this is to be used only with pages
obtained with kmap(), which doesn't seem to be the case here. On some
ARM processors it isn't even implemented (kunmap does the necessary
flushing).

-- 
Catalin

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