linux-kernel - Re: [PATCH] vfio: Fix endianness handling for emulated BARs

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Message-ID: <1403646877.4587.184.camel@pasglop>
Date:	Wed, 25 Jun 2014 07:54:37 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Alexey Kardashevskiy <aik@...abs.ru>
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	Alexander Graf <agraf@...e.de>, linuxppc-dev@...ts.ozlabs.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com>
Subject: Re: [PATCH] vfio: Fix endianness handling for emulated BARs

On Wed, 2014-06-25 at 00:33 +1000, Alexey Kardashevskiy wrote:
> 
> I do not understand why @val is considered LE here and need to be
> converted
> to CPU. Really. I truly believe it should be cpu_to_le32().

No. Both are slightly wrong semantically but le32_to_cpu() is less
wrong :-)

iowrite32 supposedly takes a "cpu" value as argument and writes an "le"
value. So if anything, you need something that converts to a "cpu" value
before you call iowrite32.

Now it's still slightly wrong because the "input" to le32_to_cpu() is
supposed to be an "LE" value but of course here it's not, it's a "cpu"
value too :-)

But yes, I agree with aw here, either do nothing or stick a set of
iowriteXX_native or something equivalent in the generic iomap header,
define them in term of iowrite32be/iowrite32 based on the compile time
endian of the arch.

Hitting asm-generic/iomap.h I think will cover all archs except ARM.
For ARM, just hack arch/arm/asm/io.h

Cheers,
Ben.

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