linux-kernel - Re: [PATCH 17/26] ARM: pxa: pxa95x is incompatible with earlier pxa

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Date:	Sun, 9 Oct 2011 14:36:52 +0800
From:	Eric Miao <eric.y.miao@...il.com>
To:	Haojian Zhuang <haojian.zhuang@...il.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Haojian Zhuang <haojian.zhuang@...vell.com>,
	Jason Chagas <jason.chagas@...vell.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 17/26] ARM: pxa: pxa95x is incompatible with earlier pxa

On Sun, Oct 9, 2011 at 2:21 PM, Haojian Zhuang <haojian.zhuang@...il.com> wrote:
> On Sat, Oct 8, 2011 at 9:24 PM, Arnd Bergmann <arnd@...db.de> wrote:
>> On Saturday 08 October 2011 11:32:14 Haojian Zhuang wrote:
>>>
>>> Eric,
>>>
>>> At first, a new macro (ARCH_PXA_V7) is defined in
>>> arch/arm/mach-pxa/Kconfig in this patch.
>>> I prefer to move this macro to arch/arm/Kconfig.
>>
>> If we move it to arch/arm/Kconfig, I would prefer making it a global option,
>> not a pxa specific one. If we introduce a top-level CONFIG_CPU_V6PLUS
>> option, we can make a number of decisions inside of Kconfig depend on that,
>> especially as we move to allow building multiple v6/v7 platforms together,
>> or multiple v5 platforms for that matter. I believe we don't need to
>> worry about v5+v7 at this point and can instead assume that won't ever
>> happen.
>>
> Nobody is using PJ4 as v6 architecture now. CPUv6 is used in old stepping
> of Dove and MMP2. CPU_PJ4 only enables CPU_v7 in the mainline code.
>
> If we used ARCH_PXA_V7 in arch/arm/Kconfig, we would have two ARCH for
> pxa. One is ARCH_PXA, and the other is ARCH_PXA_V7. Those v5 machine
> should be based on ARCH_PXA. And the saarb, tavorevb3 should be based
> on ARCH_PXA_V7. So we can avoid to define PXA_V7_MACH_AUTO. I think
> the logic of Kconfig could be easier.

Haojian,

PXA_V7_MACH_AUTO is to by default auto enable tavorevb3 when
ARCH_PXA_V7 is selected.

>
>>> Secondly, pxa95x is both used in saarb and tavorevb3.
>>
>> The patch makes that very explicit, doesn't it?
>>
> +config PXA_V7_MACH_AUTO
> +       def_bool y
> +       depends on ARCH_PXA_V7
> +       depends on !MACH_SAARB
> +       select MACH_TAVOREVB3
> +
>
> Please check this. In your patch, SAARB and TAVOREVB3 is a mutex.

They are actually not mutually exclusive - it's a trick we use to select
MACH_TAVOREVB3 by default but this option also disappears once SAARB
is selected.

Arnd,

The 'depends on ARCH_PXA_V7' could actually be removed here, as the
option is already encapsulated in if ARCH_PXA_V7 ... endif. And this
trick won't work very well when there are more than 2 boards.

>
>>> Thirdly, PXA_V7_MACH_AUTO is unnecessary. We just need to select those
>>> machines in defconfig or define a new DT machine type to select all
>>> machines.
>>
>> Enabling them in defconfig will not help here, it still allows creating
>> an invalid configuration by disabling both saarb and tavorevb3.
>> I agree that it would be best to have a single DT machine type that can
>> handle both saarb and tavorevb3 as well as any future pxa95x based machines,
>> but nobody has implemented that yet. In the meantime, I think we should
>> have the PXA_V7_MACH_AUTO or an equivalent mechanism to enforce that at
>> least one of the two board files gets built into any kernel. This is mostly
>> important to help the 'make randconfig' builds succeed, not for actual
>> users getting it wrong accidentally.
>>
>>        Arnd
>>
>
> Exactly we need to define a single DT machine type in both arch-pxa
> and arch-mmp.
> I'll register it first.

Please go ahead.
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