[Buildroot] [PATCH 1/1] arch/arm: Add Cortex-a53 CPU

[Buildroot] [PATCH 1/1] arch/arm: Add Cortex-a53 CPU

[Matt Flax]

Adds the Cortex-a53 CPU to the target architecture variant choice. This sets
the toolchain to use cortex-a53 as the target. The effect is that various
cortex-a53 tunings are enabled for the compilation of packages.

Signed-off-by: Matt Flax <flatmax@flatmax.org>
---
 arch/Config.in.arm | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/Config.in.arm b/arch/Config.in.arm
index ee612f5..72bb744 100644
--- a/arch/Config.in.arm
+++ b/arch/Config.in.arm
@@ -170,6 +170,13 @@ config BR2_cortex_a17
 	select BR2_ARM_CPU_HAS_THUMB2
 	select BR2_ARM_CPU_ARMV7A
 	select BR2_ARCH_HAS_MMU_OPTIONAL
+config BR2_cortex_a53
+	bool "cortex-A53"
+	select BR2_ARM_CPU_HAS_ARM
+	select BR2_ARM_CPU_HAS_NEON
+	select BR2_ARM_CPU_HAS_VFPV4
+	select BR2_ARM_CPU_ARMV7A
+	select BR2_ARCH_HAS_MMU_OPTIONAL
 config BR2_cortex_m3
 	bool "cortex-M3"
 	select BR2_ARM_CPU_HAS_THUMB2
@@ -458,6 +465,7 @@ config BR2_GCC_TARGET_CPU
 	default "cortex-a12"	if BR2_cortex_a12
 	default "cortex-a15"	if BR2_cortex_a15
 	default "cortex-a17"	if BR2_cortex_a17
+	default "cortex-a53"	if BR2_cortex_a53
 	default "cortex-m3"	if BR2_cortex_m3
 	default "cortex-m4"	if BR2_cortex_m4
 	default "fa526"		if BR2_fa526
-- 
2.7.4

[Buildroot] [PATCH 1/1] arch/arm: Add Cortex-a53 CPU

[Thomas Petazzoni]

Hello,

On Fri, 19 Aug 2016 10:07:04 +1000, Matt Flax wrote:
> Adds the Cortex-a53 CPU to the target architecture variant choice. This sets
> the toolchain to use cortex-a53 as the target. The effect is that various
> cortex-a53 tunings are enabled for the compilation of packages.
> 
> Signed-off-by: Matt Flax <flatmax@flatmax.org>

The A53 is an ARM64 CPU, so it should rather be added to
Config.in.aarch64 (in which we don't yet have a CPU selection, but that
can be added).

Or are you building a 32 bits ARM system for a Cortex-A53 ? In that
case, adding it to Config.in.arm would be OK, but it's a bit annoying
that we would have to duplicate many ARM CPUs between Config.in.arm and
Config.in.aarch64.

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

[Buildroot] [PATCH 1/1] arch/arm: Add Cortex-a53 CPU

[Waldemar Brodkorb]

Hi Thomas,
Thomas Petazzoni wrote,

> Hello,
> 
> On Fri, 19 Aug 2016 10:07:04 +1000, Matt Flax wrote:
> > Adds the Cortex-a53 CPU to the target architecture variant choice. This sets
> > the toolchain to use cortex-a53 as the target. The effect is that various
> > cortex-a53 tunings are enabled for the compilation of packages.
> > 
> > Signed-off-by: Matt Flax <flatmax@flatmax.org>
> 
> The A53 is an ARM64 CPU, so it should rather be added to
> Config.in.aarch64 (in which we don't yet have a CPU selection, but that
> can be added).
> 
> Or are you building a 32 bits ARM system for a Cortex-A53 ? In that
> case, adding it to Config.in.arm would be OK, but it's a bit annoying
> that we would have to duplicate many ARM CPUs between Config.in.arm and
> Config.in.aarch64.

The new rpi3 can be compiled with optimization for cortex-a53 in ARM
32 bit mode. The aarch64 port for rpi3 isn't complete. So this might
be a use case. I fixed one issue in uCLibc-ng in the past to allow
cortex-a53 optimized builds.

best regards
 Waldemar

[Buildroot] [PATCH 1/1] arch/arm: Add Cortex-a53 CPU

[Khem Raj]

> On Aug 19, 2016, at 1:03 AM, Thomas Petazzoni <thomas.petazzoni@free-electrons.com> wrote:
> 
> Hello,
> 
> On Fri, 19 Aug 2016 10:07:04 +1000, Matt Flax wrote:
>> Adds the Cortex-a53 CPU to the target architecture variant choice. This sets
>> the toolchain to use cortex-a53 as the target. The effect is that various
>> cortex-a53 tunings are enabled for the compilation of packages.
>> 
>> Signed-off-by: Matt Flax <flatmax@flatmax.org>
> 
> The A53 is an ARM64 CPU, so it should rather be added to
> Config.in.aarch64 (in which we don't yet have a CPU selection, but that
> can be added).
> 
> Or are you building a 32 bits ARM system for a Cortex-A53 ? In that
> case, adding it to Config.in.arm would be OK, but it's a bit annoying
> that we would have to duplicate many ARM CPUs between Config.in.arm and
> Config.in.aarch64.

64bit kernel with 32bit userspace is most common usecase as of now for
a53 that I see. so you need some sort of multilib.

> 
> Thomas
> --
> Thomas Petazzoni, CTO, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com
> _______________________________________________
> buildroot mailing list
> buildroot at busybox.net
> http://lists.busybox.net/mailman/listinfo/buildroot

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[Buildroot] [PATCH 1/1] arch/arm: Add Cortex-a53 CPU

[Thomas Petazzoni]

Hello,

On Fri, 19 Aug 2016 10:47:05 -0700, Khem Raj wrote:

> > On Fri, 19 Aug 2016 10:07:04 +1000, Matt Flax wrote:  
> >> Adds the Cortex-a53 CPU to the target architecture variant choice. This sets
> >> the toolchain to use cortex-a53 as the target. The effect is that various
> >> cortex-a53 tunings are enabled for the compilation of packages.
> >> 
> >> Signed-off-by: Matt Flax <flatmax@flatmax.org>  
> > 
> > The A53 is an ARM64 CPU, so it should rather be added to
> > Config.in.aarch64 (in which we don't yet have a CPU selection, but that
> > can be added).
> > 
> > Or are you building a 32 bits ARM system for a Cortex-A53 ? In that
> > case, adding it to Config.in.arm would be OK, but it's a bit annoying
> > that we would have to duplicate many ARM CPUs between Config.in.arm and
> > Config.in.aarch64.  
> 
> 64bit kernel with 32bit userspace is most common usecase as of now for
> a53 that I see. so you need some sort of multilib.

I think on RPi3 they use a 32 bit kernel and 32 bit userspace, which
probably is what Matt was targeting. But I'd like to hear from Matt's
use case first.

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

[Buildroot] [PATCH 1/1] arch/arm: Add Cortex-a53 CPU

[Khem Raj]

> On Aug 19, 2016, at 10:49 AM, Thomas Petazzoni <thomas.petazzoni@free-electrons.com> wrote:
> 
> Hello,
> 
> On Fri, 19 Aug 2016 10:47:05 -0700, Khem Raj wrote:
> 
>>> On Fri, 19 Aug 2016 10:07:04 +1000, Matt Flax wrote:
>>>> Adds the Cortex-a53 CPU to the target architecture variant choice. This sets
>>>> the toolchain to use cortex-a53 as the target. The effect is that various
>>>> cortex-a53 tunings are enabled for the compilation of packages.
>>>> 
>>>> Signed-off-by: Matt Flax <flatmax@flatmax.org>
>>> 
>>> The A53 is an ARM64 CPU, so it should rather be added to
>>> Config.in.aarch64 (in which we don't yet have a CPU selection, but that
>>> can be added).
>>> 
>>> Or are you building a 32 bits ARM system for a Cortex-A53 ? In that
>>> case, adding it to Config.in.arm would be OK, but it's a bit annoying
>>> that we would have to duplicate many ARM CPUs between Config.in.arm and
>>> Config.in.aarch64.
>> 
>> 64bit kernel with 32bit userspace is most common usecase as of now for
>> a53 that I see. so you need some sort of multilib.
> 
> I think on RPi3 they use a 32 bit kernel and 32 bit userspace, which
> probably is what Matt was targeting. But I'd like to hear from Matt's
> use case first.

rpi3 is 32bit all the way, so this patch is fine for that case.
> 
> Thomas
> --
> Thomas Petazzoni, CTO, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com

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[Buildroot] [PATCH 1/1] arch/arm: Add Cortex-a53 CPU

[Matt Flax]

On 20/08/16 03:54, Khem Raj wrote:
>> On Aug 19, 2016, at 10:49 AM, Thomas Petazzoni <thomas.petazzoni@free-electrons.com> wrote:
>>
>> Hello,
>>
>> On Fri, 19 Aug 2016 10:47:05 -0700, Khem Raj wrote:
>>
>>>> On Fri, 19 Aug 2016 10:07:04 +1000, Matt Flax wrote:
>>>>> Adds the Cortex-a53 CPU to the target architecture variant choice. This sets
>>>>> the toolchain to use cortex-a53 as the target. The effect is that various
>>>>> cortex-a53 tunings are enabled for the compilation of packages.
>>>>>
>>>>> Signed-off-by: Matt Flax <flatmax@flatmax.org>
>>>> The A53 is an ARM64 CPU, so it should rather be added to
>>>> Config.in.aarch64 (in which we don't yet have a CPU selection, but that
>>>> can be added).
>>>>
>>>> Or are you building a 32 bits ARM system for a Cortex-A53 ? In that
>>>> case, adding it to Config.in.arm would be OK, but it's a bit annoying
>>>> that we would have to duplicate many ARM CPUs between Config.in.arm and
>>>> Config.in.aarch64.
>>> 64bit kernel with 32bit userspace is most common usecase as of now for
>>> a53 that I see. so you need some sort of multilib.
>> I think on RPi3 they use a 32 bit kernel and 32 bit userspace, which
>> probably is what Matt was targeting. But I'd like to hear from Matt's
>> use case first.
> rpi3 is 32bit all the way, so this patch is fine for that case.

My use case is 32 bit kernel with a 32 bit buildroot.

I have been working with the s5p6818 Nexcell silicon and they have A53 
cores. These cores are more powerful then ARMv7 cortex cores ... because 
they have a more advanced neon hardware floating point processor. Even 
with a 32 bit kernel and os, gcc can optimise the code using the 
"cortex-a53" tuning.
I think (at this point in time) the neon unit can handle 64bit (double) 
computations, even when the kernel is 32 bit. This can only be enabled 
in gcc using the "cortex-a53" tuning. From a hardware standpoint, if it 
is in silicon, then it will work - no matter what the software is doing 
... I guess it just depends on the 32 bit gcc implementation of being 
able to load and unload the various 64 bit types efficiently. Not sure 
where to look for more information, however Aarch32 is mentioned in the 
a53 gcc config : 
https://github.com/gcc-mirror/gcc/blob/master/gcc/config/arm/cortex-a53.md
They also mention special register load instructions for aarch32.


 From my experience, the Nexcell s5p6818 ARMv8 A53 cores roughly double 
their speed in heavy floating point execution over Exynos 4412 ARMv7 
Cortex-A9 cores. It is possible that this is because their NEON hardware 
processors have double the vector size ?

Matt

>> Thomas
>> --
>> Thomas Petazzoni, CTO, Free Electrons
>> Embedded Linux and Kernel engineering
>> http://free-electrons.com
>
>
> _______________________________________________
> buildroot mailing list
> buildroot at busybox.net
> http://lists.busybox.net/mailman/listinfo/buildroot

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