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Date:	Mon, 7 Apr 2014 22:00:28 +0200
From:	Borislav Petkov <>
To:	Jason Baron <>, "H. Peter Anvin" <>,
	Ingo Molnar <>,
	Thomas Gleixner <>
Subject: Re: [PATCH 0/3] Add new ie31200_edac driver

On Fri, Apr 04, 2014 at 09:13:45PM +0000, Jason Baron wrote:
> Hi,
> Add support for memory errors for the Intel E3-1200 processors.
> While testing the driver, I found that doing a readq() on the
> memory mapped memory controller hub registers caused a hard lockup
> on my x86_64 system. It turns out that a read across a DW boundary
> is a no no here.
> "
> Software must not access B0/D0/F0 32-bit memory-mapped registers with
> requests that cross a DW boundary.
> "
> ( p. 16)
> Thus, I've added a generic lo_hi_[read|write]_q API, to deal with
> this issue.
> I think longer term the right thing is maybe to simply add these
> definitions to include/asm-generic/io.h, as I didn't see any
> in tree users of 'io-64-nonatomic-hi-lo.h', and simply remove
> io-64-nonatomic-hi-lo.h and io-64-nonatomic-lo-hi.h. But I didn't want to
> tie that cleanup to this edac driver submission.

Makes sense to me. There are a couple of drivers which include
io-64-nonatomic-lo-hi.h though.

As part of the cleanup, it might be even clearer to do the lo_hi_* calls
directly instead of the readq/writeq defines as a means of documenting
that this particular code cannot stomach doubleword-crossing accesses.

x86 guys, opinions? Especially patch 1/3, should I pick it up or you



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