Re: [PATCH] hw/mips/gt64xxx_pci: Don't endian-swap GT_PCI0_CFGADDR

From: Rob Landley <rob@landley.net>
To: "Philippe Mathieu-Daudé" <philmd@linaro.org>,
	"Nathan Chancellor" <nathan@kernel.org>
Cc: "Jiaxun Yang" <jiaxun.yang@flygoat.com>,
	qemu-devel@nongnu.org, balaton@eik.bme.hu,
	"Bernhard Beschow" <shentey@gmail.com>,
	"Thomas Huth" <thuth@redhat.com>,
	"Daniel P. Berrangé" <berrange@redhat.com>,
	"Peter Maydell" <peter.maydell@linaro.org>
Subject: Re: [PATCH] hw/mips/gt64xxx_pci: Don't endian-swap GT_PCI0_CFGADDR
Date: Thu, 30 Mar 2023 08:12:54 -0500	[thread overview]
Message-ID: <c8fd4b42-7c7b-8e65-5fe6-ed7d02644725@landley.net> (raw)
In-Reply-To: <cf1deca3-49ef-06a3-0f20-92c25968ae7d@linaro.org>

On 3/29/23 12:23, Philippe Mathieu-Daudé wrote:
> On 29/3/23 18:48, Rob Landley wrote:
>>>> Works fine for me. Somebody said it was the wrong fix but I don't remember why...
>>>
>>> This is a correct /partial/ fix. With this patch, Malta works on little
>>> endian hosts. No luck with big-endian hosts, but this was broken
>>> previous to 3db29dcac2 rework, so apparently not a big deal ¯\_(ツ)_/¯
>> 
>> No, big endian worked for me with that patch?
>> 
>> The build in my $PATH is QEMU emulator version 7.2.50
>> (v7.2.0-873-g65cc5ccf06-dirty) with that patch, and if you wget
>> https://landley.net/toybox/downloads/binaries/mkroot/0.8.9/mips.tgz and
>> ./run-emulator.sh in there, the virtual net can wget http://site (the sample
> 
> Oh, we are having some QEMU semantic confusion here...
> 
> You are testing a QEMU big-endian *guest* (or "target") in this example.
> 
> I presume you are testing on a little-endian *host* (x86_64, aarch64,
> ppc64el or mips64el).

Ah, yes.

I have not tried running qemu on a big endian host system in forever, but there
are some IBM people with great interest in supporting every possible thing on
s390x. Elizabeth Joseph would be one and would know a bunch more:

https://floss.social/@pleia2/110095815201601529

>> image hasn't got https:// support enabled because I didn't include the build
>> dependency), and the virtual disk works (if you do "./run-emulator.sh -hda
>> blah.img" anyway, the test wrapper I mentioned creates a squashfs image for it
>> to mount)). Without the patch I don't even get a PCI bus. Running "file
>> /bin/toybox" says MSB, and the mipsel image is the little endian one anyway. I
> 
> Here you describe the little-endian MIPS *target* image.

Which was broken without that patch, yes. So that's why the fix was "partial"...

>> also test s390x (which is big endian 64 bit), but I don't think this needed a
>> patch? (Hadn't been broken last I checked?)
> 
> Here you describe big-endian s390x *target* image.

I don't have s390x hardware to run it on. I do have an sh2eb board but it's
nommu and only has 128 megs of ram, so running qemu on it would be... unlikely.

> I expect if you run your test with QEMU v7.2.0-873-g65cc5ccf06-dirty
> on any big-endian *host* (like a s390x), the test fails.

I don't have powerpc mac hardware, which seems the easiest way to get such a
test system.

(Well, ok, the EASY way would be to feed qemu-system-s390x a couple gigs of ram
and then build and run qemu within qemu. While I do have a native toolchain for
s390x, qemu's grown an insane dependency stack these days that would be a pain
to bootstrap under a musl beyond-linux-from-scratch environment...)

Rob