linux-kernel - Re: [PATCH 3/3] arm64: configs: unset CPU_BIG

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Message-ID: <e6df09ba-a016-65c0-5b56-f7b91a7c9dd8@huawei.com>
Date:   Mon, 14 Oct 2019 14:12:03 +0800
From:   Hanjun Guo <guohanjun@...wei.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Will Deacon <will@...nel.org>,
        Anders Roxell <anders.roxell@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        John Garry <john.garry@...wei.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Olof Johansson <olof@...om.net>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/3] arm64: configs: unset CPU_BIG_ENDIAN

Hi Arnd,

On 2019/10/12 22:05, Arnd Bergmann wrote:
> On Sat, Oct 12, 2019 at 9:33 AM Hanjun Guo <guohanjun@...wei.com> wrote:
>>
>> On 2019/10/11 18:27, Will Deacon wrote:
>> [...]
>>>
>>> Does anybody use BIG_ENDIAN? If we're not even building it then maybe we
>>> should get rid of it altogether on arm64. I don't know of any supported
>>> userspace that supports it or any CPUs that are unable to run little-endian
>>> binaries.
>>
>> FWIW, massive telecommunication products (based on ARM64) form Huawei are using
>> BIG_ENDIAN, and will use BIG_ENDIAN in the near future as well.
> 
> Ok, thanks for the information -- that definitely makes it clear that
> it cannot go
> away anytime soon (though it doesn't stop us from change the
> allmodconfig default
> if we decide that's a good idea).

I agree with you.

> 
> Do you know if there are currently any patches against mainline to
> make big-endian
> work in products, or is everything working out of the box?

We are not using mainline kernel for product, but LTS 4.4 is working
fine, and also we tested LTS 4.19 kernel without any other big-endian
patches, the latest big-endian bug we found is this:

a6002ec5a8c6 arm64: opcodes.h: Add arm big-endian config options before including arm header

The running kernel code covered but Huawei's telecommunication products
is limited, but I think ARM64 arch code is working fine for big-endian.

Thanks
Hanjun