linux-kernel - Re: [PATCH 3/4] arch: define CONFIG_PAGE_SIZE

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Message-Id: <164616c2-94f6-40e8-86e0-850dc8da212e@app.fastmail.com>
Date: Tue, 27 Feb 2024 11:59:01 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Geert Uytterhoeven" <geert@...ux-m68k.org>,
 "Arnd Bergmann" <arnd@...nel.org>
Cc: "Thomas Gleixner" <tglx@...utronix.de>,
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Subject: Re: [PATCH 3/4] arch: define CONFIG_PAGE_SIZE_*KB on all architectures

On Tue, Feb 27, 2024, at 09:54, Geert Uytterhoeven wrote:
> Hi Arnd,
>> diff --git a/arch/m68k/Kconfig.cpu b/arch/m68k/Kconfig.cpu
>> index 9dcf245c9cbf..c777a129768a 100644
>> --- a/arch/m68k/Kconfig.cpu
>> +++ b/arch/m68k/Kconfig.cpu
>> @@ -30,6 +30,7 @@ config COLDFIRE
>>         select GENERIC_CSUM
>>         select GPIOLIB
>>         select HAVE_LEGACY_CLK
>> +       select HAVE_PAGE_SIZE_8KB if !MMU
>
> .... if you would drop the !MMU-dependency here.
>
>>
>>  endchoice
>>
>> @@ -45,6 +46,7 @@ config M68000
>>         select GENERIC_CSUM
>>         select CPU_NO_EFFICIENT_FFS
>>         select HAVE_ARCH_HASH
>> +       select HAVE_PAGE_SIZE_4KB
>
> Perhaps replace this by
>
>     config M68KCLASSIC
>             bool "Classic M68K CPU family support"
>             select HAVE_ARCH_PFN_VALID
>   +         select HAVE_PAGE_SIZE_4KB if !MMU
>
> so it covers all 680x0 CPUs without MMU?

I was a bit unsure about how to best do this since there
is not really a need for a fixed page size on nommu kernels,
whereas the three MMU configs clearly tie the page size to
the MMU rather than the platform.

There should be no reason for coldfire to have a different
page size from dragonball if neither of them actually uses
hardware pages, so one of them could be changed later.

Let me know if that makes sense to you, or you still
prefer me to change it like you suggested.

      Arnd