[Buildroot] [PATCH 3/4 v2] arch/arm: add big.LITTLE cpu variants

[Yann E. MORIN]

Arnout, All,

On 2017-07-08 18:34 +0200, Arnout Vandecappelle spake thusly:
> On 08-07-17 16:08, Yann E. MORIN wrote:
> > The big.LITTLE configurations can be optimised for by gcc, and a few
> > users wonder what they should choose when they have such CPUs.
> > 
> > Add new entries for those big.LITTLE configurations.
> > 
> > Signed-off-by: "Yann E. MORIN" <yann.morin.1998 at free.fr>
> > Cc: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
> > Cc: Thomas De Schampheleire <patrickdepinguin at gmail.com>
> > Cc: Baruch Siach <baruch at tkos.co.il>
> [snip]
> > +config BR2_cortex_a15_a7
> > +	bool "cortex-A15/A7 big.LITTLE"
> > +	select BR2_ARM_CPU_HAS_ARM
> > +	select BR2_ARM_CPU_HAS_NEON
> > +	select BR2_ARM_CPU_HAS_VFPV4
> > +	select BR2_ARM_CPU_HAS_THUMB2
> > +	select BR2_ARM_CPU_ARMV7A
> > +	select BR2_ARCH_HAS_MMU_OPTIONAL
> 
>  Not for this patch, but: is this actually correct? Looking at the kernel's
> arch/arm/Kconfig, I see that all the platforms that can be selected when MMU is
> not selected are <= ARMv6. Well, I'm not entirely sure, it's a bit difficult to
> map stuff like CPU_XSC3 on an ARM version.

I just duplicated for a15-a7 what we had for a15 and a7, which
fortunately was exactly identical. So a15-a7 can be noMMU in Buildroot.

Does that make sense? Probably not, but this should be fixed by another
patch, then.

> > +	depends on !BR2_ARCH_IS_64
> [snip]
> > diff --git a/package/gcc/Config.in.host b/package/gcc/Config.in.host
> > index 5dcaa03ff0..c072b78ae5 100644
> > --- a/package/gcc/Config.in.host
> > +++ b/package/gcc/Config.in.host
> > @@ -25,7 +25,8 @@ config BR2_GCC_VERSION_4_9_X
> >  	# Broken or unsupported architectures
> >  	depends on !BR2_arc && !BR2_bfin && !BR2_or1k
> >  	# Broken or unsupported ARM cores
> > -	depends on !BR2_cortex_a17 && !BR2_cortex_a72
> > +	depends on !BR2_cortex_a17 && !BR2_cortex_a17_a7
> > +	depends on !BR2_cortex_a72 && !BR2_cortex_a72_a53
> >  	# Unsupported MIPS cores
> >  	depends on !BR2_mips_interaptiv
> >  	# Unsupported for MIPS R5
> > @@ -45,6 +46,8 @@ config BR2_GCC_VERSION_5_X
> >  	bool "gcc 5.x"
> >  	# Broken or unsupported architectures
> >  	depends on !BR2_arc && !BR2_bfin && !BR2_or1k
> > +	# Broken or unsupported ARM cores
> > +	depends on !BR2_cortex_a57_a53 && !BR2_cortex_a72_a53
> 
>  According to [1], a72.a53 was added in GCC 5. And a57.a53 was already added in
> GCC 4.9 - is it broken in GCC 5?

I indeed tried various versions of gcc, starting with gcc-4.9.

The depednencies I added here are based on brokenness of versions
earlier than that.

> >  	# musl ppc64 unsupported
> >  	depends on !(BR2_TOOLCHAIN_USES_MUSL && (BR2_powerpc64 || BR2_powerpc64le))
> >  	# Unsupported MIPS cores
> > diff --git a/toolchain/toolchain-external/toolchain-external-codesourcery-aarch64/Config.in b/toolchain/toolchain-external/toolchain-external-codesourcery-aarch64/Config.in
> > index 2fbb218ecc..66a032e9ac 100644
> > --- a/toolchain/toolchain-external/toolchain-external-codesourcery-aarch64/Config.in
> > +++ b/toolchain/toolchain-external/toolchain-external-codesourcery-aarch64/Config.in
> > @@ -1,6 +1,8 @@
> >  config BR2_TOOLCHAIN_EXTERNAL_CODESOURCERY_AARCH64
> >  	bool "CodeSourcery AArch64 2014.11"
> >  	depends on BR2_aarch64
> > +	# a57/a53 and a72/a53 appeared in gcc-6 or were broken before
> 
>  Ah, here you mention it. Better raise that to the commit message. Do you also
> have a reference for it?

No, except that gcc did not build: the brokenness manifested itself with
gcc's configure script refusing the big-LITTLE variants.

Regards,
Yann E. MORIN.

>  Regards,
>  Arnout
> 
> 
> > +	depends on !BR2_cortex_a57_a53 && !BR2_cortex_a72_a53
> [snip]
> 
> [1] https://gcc.gnu.org/gcc-5/changes.html
> 
> -- 
> Arnout Vandecappelle                          arnout at mind be
> Senior Embedded Software Architect            +32-16-286500
> Essensium/Mind                                http://www.mind.be
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