linux-kernel - Re: [PATCH] arm64: Kconfig: add a choice for endianess

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Date:   Tue, 12 Nov 2019 17:27:54 +0000
From:   Will Deacon <will@...nel.org>
To:     John Garry <john.garry@...wei.com>
Cc:     Anders Roxell <anders.roxell@...aro.org>, catalin.marinas@....com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: Kconfig: add a choice for endianess

On Tue, Nov 12, 2019 at 04:24:31PM +0000, John Garry wrote:
> On 12/11/2019 16:01, Anders Roxell wrote:
> > When building allmodconfig KCONFIG_ALLCONFIG=$(pwd)/arch/arm64/configs/defconfig
> > CONFIG_CPU_BIG_ENDIAN gets enabled. Which tends not to be what most
> > people wants. Another concern that thas come up is that ACPI in't built
> 
> /s/wants/want/, s/thas/has/, s/in't/isn't/
> 
> > for an allmodconfig kernel today since that also depends on !CPU_BIG_ENDIAN.
> > 
> > Rework so that we introduce a 'choice' and default the choice to
> > CPU_LITTLE_ENDIAN. That means that when we build an allmodconfig kernel
> > it will default to CPU_LITTLE_ENDIAN that most people tends to want.
> > 
> > Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
> 
> FWIW, apart from spelling mistakes:
> 
> Reviewed-by: John Garry <john.garry@...wei.com>
> 
> > ---
> >   arch/arm64/Kconfig | 13 +++++++++++++
> >   1 file changed, 13 insertions(+)
> > 
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index 64764ca92fca..62f83c234a61 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -877,11 +877,24 @@ config ARM64_PA_BITS
> >   	default 48 if ARM64_PA_BITS_48
> >   	default 52 if ARM64_PA_BITS_52
> > +choice
> > +	prompt "Endianess"
> 
> Should this be "Endianness"?
> 
> > +	default CPU_LITTLE_ENDIAN
> > +	help
> > +	  Choose what mode you plan on running your kernel in.

While we're at it, I'd avoid the use of "mode" here since that has a
different meaning in the architecture, although I see we already use that
terminology for CPU_BIG_ENDIAN. How about:

  "Select the endianness of data accesses performed by the CPU. Userspace
   applications will need to be compiled and linked for the endianness
   that is selected here.

   Little-endian is compatible with x86, but big-endian is faster."

(ok, maybe drop that last sentence ;)

> >   config CPU_BIG_ENDIAN
> >          bool "Build big-endian kernel"
> >          help
> >            Say Y if you plan on running a kernel in big-endian mode.

Then this can be:

  "Say Y if you plan on running a kernel with a big-endian userspace."

> > +config CPU_LITTLE_ENDIAN
> > +	bool "Build little-endian kernel"
> > +	help
> > +	  Say Y if you plan on running a kernel in little-endian mode.


  "Say Y if you plan on running a kernel with a little-endian userspace.
   This is usually the case for distributions targetting arm64."

I think it's userspace that people really care about, so wording it in
terms of that makes most sense to me.

Will