Re: [Buildroot] [PATCH v2 1/5] arch/Config.in.xtensa: adjust endianness logic to avoid bogus configurations

[Thomas Petazzoni via buildroot <buildroot@buildroot.org>]

Hello,

Sorry to bring back this topic only now, but there are still Xtensa
issues that we need to resolve, and this series was aiming at solving
them. But I have further questions.

On Sun, 25 Sep 2022 12:10:41 +0200
"Yann E. MORIN" <yann.morin.1998@free.fr> wrote:

> > diff --git a/arch/Config.in.xtensa b/arch/Config.in.xtensa
> > index f9d5adb4c9..4bb58e1964 100644
> > --- a/arch/Config.in.xtensa
> > +++ b/arch/Config.in.xtensa
> > @@ -37,6 +37,10 @@ config BR2_XTENSA_LITTLE_ENDIAN
> >  
> >  config BR2_XTENSA_BIG_ENDIAN
> >  	bool "Big endian"
> > +	# Internal toolchains without an overlay file are always
> > +	# little-endian, so we prevent from selecting big endian in
> > +	# this case.
> > +	depends on BR2_XTENSA_OVERLAY_FILE != "" || BR2_TOOLCHAIN_EXTERNAL  
> 
> I think that dependency should go to the whole choice instead:
> 
>     choice
>         prompt "Target Architecture Endianness"
>         default BR2_XTENSA_LITTLE_ENDIAN
>         depends on BR2_XTENSA_CUSTOM || BR2_TOOLCHAIN_EXTERNAL

My memory is probably vague, but I don't see how this solve the
problem. The problem was to prevent the user from choosing "big endian"
if he has selected a custom core but not specified an overlay.

> This should cover the external toolchain case, and the internal
> toolchain for a custom core (assuming we keep the no-empty overlay for
> custom cores).

Not sure what you mean by "assuming we keep the no-empty overlay for
custom cores".

> 
> I.e. semantically, choosing between big or little is not about having or
> not having an overlay, but about being a custom core or not (or using a
> custom toolchain).

Not sure to follow you here. The only issue is precisely that if you
don't specify an overlay, there is no way your custom Xtensa core can
be big endian: it will be little endian. The configuration we want to
prevent the user from creating is: custom core, no overlay, big endian.

Best regards,

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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