Re: [Qemu-devel] [Qemu-ppc] [PATCH v3 11/14] ioport: Switch dispatching to memory core layer

From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Anthony Liguori <anthony@codemonkey.ws>
Cc: "Peter Maydell" <peter.maydell@linaro.org>,
	"Liu Ping Fan" <pingfank@linux.vnet.ibm.com>,
	"Alexander Graf" <agraf@suse.de>,
	"qemu-devel Developers" <qemu-devel@nongnu.org>,
	"qemu-ppc@nongnu.org list:PowerPC" <qemu-ppc@nongnu.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Jan Kiszka" <jan.kiszka@web.de>,
	"Andreas Färber" <afaerber@suse.de>,
	"Hervé Poussineau" <hpoussin@reactos.org>
Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH v3 11/14] ioport: Switch dispatching to memory core layer
Date: Tue, 16 Jul 2013 00:16:19 +1000	[thread overview]
Message-ID: <1373897779.19894.351.camel@pasglop> (raw)
In-Reply-To: <87sizfudli.fsf@codemonkey.ws>

On Mon, 2013-07-15 at 09:01 -0500, Anthony Liguori wrote:
> On PPC, le_mode only really affects load/stores and instruction
> decoding.  Any shared data structures between the CPU and OS remain big
> endian.

Translation:

On ppc with the specific machine type "pseries" which emulates a
paravirtualized environment, the data structures between the guest and
the hypervisor remain big endian :-)

But this is essentially irrelevant to the basic discussion about endian
handling (ie. PCI devices remain LE, etc...).

Point is, TCG can deal with dual endian reasonably easily. The main
issues are around things like virtio with its stupid concept of "guest
endian" (wtf does guest endian means on a dual endian processor ?) but I
think we've whacked Rusty's head plenty enough on that one... and it's
not that hard to work around.

> So TARGET_WORDS_BIGENDIAN is still accurate even when le_mode=1.  It's
> not the semantic equivalent of changing TARGET_WORDS.

The point is that it's unnecessary :-) IE. We should aim to get rid of
the concept of target endianness altogether :-)

Cheers,
Ben.