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

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Message-ID: <CAK8P3a0kBz1-i-3miCo1vMuoM39ivXa3oxOE9VnCqDO-nfNOxw@mail.gmail.com>
Date:   Fri, 11 Oct 2019 12:25:29 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     John Garry <john.garry@...wei.com>
Cc:     Anders Roxell <anders.roxell@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Olof Johansson <olof@...om.net>
Subject: Re: [PATCH 3/3] arm64: configs: unset CPU_BIG_ENDIAN

On Thu, Oct 3, 2019 at 1:15 PM John Garry <john.garry@...wei.com> wrote:
> On 03/10/2019 08:40, Anders Roxell wrote:
> > On Tue, 1 Oct 2019 at 16:04, John Garry <john.garry@...wei.com> wrote:
> >> On 26/09/2019 20:30, Anders Roxell wrote:
> >>> it doesn't get enabled when building allmodconfig kernels. When doing a
> >>> 'make savedefconfig' CONFIG_CPU_BIG_ENDIAN will be dropped.
> >>
> >> So without having to pass KCONFIG_ALLCONFIG or do anything else, what
> >> about a config for CONFIG_CPU_LITTLE_ENDIAN instead? I'm not sure if
> >> that was omitted for a specific reason.
> >
> > Oh, I tried to elaborate on the idea in the cover letter, that using
> > the defconfig
> > as base and then configure the rest as modules is to get a bootable kernel
> > that have as many features turned on as possible. That will make it possible
> > to run as wide a range of testsuites as possible on a single kernel.
> >
> > Does that make it clearer ?
>
> Hi Anders,
>
> Yeah, I got the idea.
>
> So when you say "'make savedefconfig' CONFIG_CPU_BIG_ENDIAN will be
> dropped", I don't know what the rules are in terms of resyncing the
> common defconfig (I was under the impression that it's done per release
> cycle by the arm soc maintainers, but can't find evidence as such), but
> your change may be easily lost in this way.

We don't do it every release, but occasionally someone sends a patch
with a refresh, and this might easily get missed.

We could force the allmodconfig kernel to be little-endian by default,
using a choice statement to pick endianess like arch/mips and arch/sh
do, the effect would be that an allmodconfig kernel gains a few more
options that depend on !BIG_ENDIAN, but we would no longer catch
a class of endianess bugs in drivers that we otherwise get warnings
for. No idea what is better here.

       Arnd