linux-kernel - Re: memcpy_fromio in dmi

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Message-ID: <20130425100246.GR3672@sgi.com>
Date:	Thu, 25 Apr 2013 05:02:46 -0500
From:	Robin Holt <holt@....com>
To:	Jean Delvare <jdelvare@...e.de>
Cc:	"Luck, Tony" <tony.luck@...el.com>,
	DuanZhenzhong <zhenzhong.duan@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Yu, Fenghua" <fenghua.yu@...el.com>
Subject: Re: memcpy_fromio in dmi_scan.c

On Wed, Apr 24, 2013 at 09:22:08PM +0200, Jean Delvare wrote:
> Hi Tony,
> 
> Thanks for stepping in.
> 
> Le Tuesday 23 April 2013 à 22:00 +0000, Luck, Tony a écrit :
> > > I don't have much knowledge about IA64 either. All I see is that while
> > > x86 implements memcpy_fromio() with memcpy [1], ia64 implements it with
> > > readb [2]. There must be a reason for that, and I can only suppose that
> > > memcpy on __iomem pointers doesn't work on IA64. If memcpy doesn't work
> > > then I can't see memcmp working.
> > 
> > On most platforms readb() just ends up doing a regular dereference of the
> > address ... so I'd expect that memcmp would work just fine.  The exception
> > is the old SGI sn2 which end up calling ___sn_readb() ... which does something
> > weird with sn_dma_flush() after doing the dereference of *addr.  I don't

sn_dma_flush has a good description at the beginning of it.  It is only
related to activity on PCI attached devices and a memcmp should be fine.
It must be that our prom produces a bad DMI table.

Robin
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