linux-kernel - Re: [PATCH 1/2] armv8: aarch32: Execute 32-bit Linux for LayerScape platforms

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Date:   Fri, 23 Sep 2016 14:18:31 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Stuart Yoder <stuart.yoder@....com>,
        Alison Wang <b18965@...escale.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        Fabio Estevam Estevam <fabio.estevam@....com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Scott Wood <scott.wood@....com>, Leo Li <leoyang.li@....com>
Cc:     Jason Jin <jason.jin@....com>
Subject: Re: [PATCH 1/2] armv8: aarch32: Execute 32-bit Linux for LayerScape
 platforms

On 23/09/16 14:13, Stuart Yoder wrote:
> 
> 
>> -----Original Message-----
>> From: Robin Murphy [mailto:robin.murphy@....com]
>> Sent: Friday, September 23, 2016 7:17 AM
>> To: Alison Wang <b18965@...escale.com>; shawnguo@...nel.org; kernel@...gutronix.de; Fabio Estevam
>> Estevam <fabio.estevam@....com>; linux@...linux.org.uk; linux-arm-kernel@...ts.infradead.org; linux-
>> kernel@...r.kernel.org; Scott Wood <scott.wood@....com>; Stuart Yoder <stuart.yoder@....com>; Leo Li
>> <leoyang.li@....com>
>> Cc: Jason Jin <jason.jin@....com>
>> Subject: Re: [PATCH 1/2] armv8: aarch32: Execute 32-bit Linux for LayerScape platforms
>>
>> Hi Alison,
>>
>> On 23/09/16 03:19, Alison Wang wrote:
>>> The ARMv8 architecture supports:
>>> 1. 64-bit execution state, AArch64.
>>> 2. 32-bit execution state, AArch32, that is compatible with previous
>>> versions of the ARM architecture.
>>>
>>> LayerScape platforms are compliant with ARMv8 architecture. This patch
>>> is to support running 32-bit Linux kernel for LayerScape platforms.
>>>
>>> Verified on LayerScape LS1043ARDB, LS1012ARDB, LS1046ARDB boards.
>>>
>>> Signed-off-by: Ebony Zhu <ebony.zhu@....com>
>>> Signed-off-by: Alison Wang <alison.wang@....com>
>>> ---
>>>  arch/arm/Kconfig                    |  9 +++++++++
>>>  arch/arm/mach-imx/Kconfig           | 14 ++++++++++++++
>>>  arch/arm/mach-imx/Makefile          |  4 +++-
>>>  arch/arm/mach-imx/mach-layerscape.c | 23 +++++++++++++++++++++++
>>>  4 files changed, 49 insertions(+), 1 deletion(-)
>>>  create mode 100644 arch/arm/mach-imx/mach-layerscape.c
>>>
>>> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
>>> index f0c8068..e8d470e 100644
>>> --- a/arch/arm/Kconfig
>>> +++ b/arch/arm/Kconfig
>>> @@ -294,6 +294,15 @@ config PGTABLE_LEVELS
>>>  	default 3 if ARM_LPAE
>>>  	default 2
>>>
>>> +config ARCH_AARCH32_ES_SUPPORT
>>> +	def_bool n
>>> +	help
>>> +	 The ARMv8 architecture supports 64-bit execution state, AArch64
>>> +	 and 32-bit execution state, AArch32, that is compatible with
>>> +	 previous versions of the ARM architecture.
>>> +
>>> +	 Enable AArch32 execution state support for ARMv8 architecture.
>>
>> What's this supposed to do, exactly? I've been running 32-bit kernels on
>> my Juno with very little issue (beyond a couple of DT tweaks, and some
>> firmware hacks with a corresponding bit of A64 assembly tacked on the
>> front of the zImage to switch into AArch32 state).
> 
> Which arch/arm/mach-* platform are you using for Juno?

I don't even know! :) I just start with a multi_v7_defconfig plus a few
extra bits (LPAE, KVM, sil24, sky2, etc.) and it works. I guess it's the
combination of mach-vexpress and mach-virt.

Robin.

> 
> Thanks,
> Stuart
>