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Re: [Qemu-trivial] [Qemu-devel] [PATCH v2 07/14] sm501: Fix device endia

From: Peter Maydell
Subject: Re: [Qemu-trivial] [Qemu-devel] [PATCH v2 07/14] sm501: Fix device endianness
Date: Sat, 4 Mar 2017 12:40:17 +0000

On 3 March 2017 at 20:11, BALATON Zoltan <address@hidden> wrote:
> On Fri, 3 Mar 2017, Peter Maydell wrote:
>> So what cases have you tested? The Linux kernel seems to support:
>> * sh embedded device, little endian
>> * PCI card, little endian host
>> * PCI card, big endian host
>> and there are also
>> * 16 bit pixel format
>> * 32 bit pixel format
>> which makes 6 different combinations.
>> (It's a shame there's no sh4 BE code to run on this.)
> As mentioned before I've used this image to test SH:
> https://people.debian.org/~aurel32/qemu/sh4/
> with video=800x600-16 kernel parameter where changing -16 to different bit
> depths (8, 32) reproduces the problem. On ppc I've tested with MorphOS which
> uses 16 bpp, Linux and U-boot which I think uses 8 bit. These run on real
> hardware so I think if they work the emulation should be OK.
> You've said before that PCI is likely always little endian and SH embedded
> is LE too so unless something uses the device in BE mode (which we don't
> emulate) setting it to little endian should be correct. For frame buffer
> endianness I can only go with what I've seen clients doing and my patch does
> what worked for the above on SH and PPC. I can't prove it's correct but
> works for the systems I've targeted and also fixes the SH case which seemed
> to be broken.

Right, but we should test the PCI-on-a-little-endian CPU
case, because right now your code has #ifdef TARGET_WORDS_BIGENDIAN
in it which means that the PCI device will behave differently
on big and little endian CPUs, and you have a case that you
haven't tested.

(At the moment with the set of cases you've tested the
sh embedded device ones will always be using the "not
TARGET_WORDS_BIGENDIAN" code and the PCI-on-PPC will
always use the "is TARGET_WORDS_BIGENDIAN" code. But
TARGET_WORDS_BIGENDIAN set/not set is orthogonal to

-- PMM

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