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

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D17263229@AcuExch.aculab.com>
Date:	Tue, 24 Jun 2014 14:40:07 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Alexey Kardashevskiy' <aik@...abs.ru>,
	Alex Williamson <alex.williamson@...hat.com>,
	Alexander Graf <agraf@...e.de>
CC:	Nikunj A Dadhania <nikunj@...ux.vnet.ibm.com>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: RE: [PATCH] vfio: Fix endianness handling for emulated BARs

From: Alexey Kardashevskiy
...
> >> So IMHO we should either create new, generic iowrite helpers that don't
> >> do any endian swapping at all or do iowrite32(cpu_to_le32(val)) calls.
> >
> > I'm one of those people for whom iowrite32(le32_to_cpu(val)) makes sense
> 
> 
> 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().

Think about it carefully...

Apparently iowrite32() is writing a 'cpu' value out 'le'.
So if you have a 'le' value you need to convert it to 'cpu' first.

I really won't ask how 'be' ppc managed to get 'le' on-chip peripherals.

	David