linux-kernel - Re: [PATCH] loongarch: Disable FIX_EARLYCON_MEM when ARCH

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Message-Id: <6160921c-7761-46d1-9d13-f26af5873b2e@app.fastmail.com>
Date: Fri, 03 Jan 2025 09:41:44 +0000
From: "Jiaxun Yang" <jiaxun.yang@...goat.com>
To: "Huacai Chen" <chenhuacai@...nel.org>
Cc: "Xuerui Wang" <kernel@...0n.name>, loongarch@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] loongarch: Disable FIX_EARLYCON_MEM when ARCH_IOREMAP is enabled



在2025年1月3日一月 上午9:35，Huacai Chen写道：
> On Fri, Jan 3, 2025 at 5:02 PM Jiaxun Yang <jiaxun.yang@...goat.com> wrote:
>>
>>
>>
>> 在2025年1月3日一月 上午2:38，Huacai Chen写道：
>> > Hi, Jiaxun,
>> >
>> > On Thu, Jan 2, 2025 at 10:34 PM Jiaxun Yang <jiaxun.yang@...goat.com> wrote:
>> >>
>> >> When ARCH_IOREMAP is enabled, we are using always accessible DMW
>> >> for ioremap. It makes no sense to create a dedicated mapping for
>> >> earlycon given that we can access the region via DMW.
>> >>
>> >> Disable FIX_EARLYCON_MEM when ARCH_IOREMAP is selected. This can
>> >> ease debugging for early mapping issues.
>> > Fixmap has nothing to do with IOREMAP, whether you use ARCH_IOREMAP or
>> > GENERIC_IOREMAP, earlycon is mapped by fixmap rather than ioremap().
>>
>> When you have ARCH_IOREMAP it’s not necessary to create fixed map for earlycon.
>>
>> As ioremap along is sufficient to access MMIO.
> It's sufficient but ioremap() doesn't need to control everything about
> MMIO, and I don't like the #ifdef in fixmap.h.

It’s fine do drop that ifdef and keep Kconfig change.

I can do it in v2.

Thanks
-Jiaxun

>
> Huacai
>>
>> I’m doing this as it can help with debugging early mapping issues.
>>
>> Thanks
>>
>> >
>> > Huacai
>> >
>> >>
>> >> Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.com>
>> >> ---
>> >>  arch/loongarch/Kconfig              | 2 +-
>> >>  arch/loongarch/include/asm/fixmap.h | 2 ++
>> >>  2 files changed, 3 insertions(+), 1 deletion(-)
>> >>
>> >> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
>> >> index 1c4d13aa677e2e04b9791882fba7523f93d6a69d..ad8a8cf75343799ea626be52f521fa75e7cbe07b 100644
>> >> --- a/arch/loongarch/Kconfig
>> >> +++ b/arch/loongarch/Kconfig
>> >> @@ -246,7 +246,7 @@ config MACH_LOONGSON64
>> >>         def_bool 64BIT
>> >>
>> >>  config FIX_EARLYCON_MEM
>> >> -       def_bool y
>> >> +       def_bool !ARCH_IOREMAP
>> >>
>> >>  config PGTABLE_2LEVEL
>> >>         bool
>> >> diff --git a/arch/loongarch/include/asm/fixmap.h b/arch/loongarch/include/asm/fixmap.h
>> >> index d2e55ae55bb9c499b9a685509bc26d663054b58e..905dc7a5f9fa52ac924fe832749f39283c28a9f8 100644
>> >> --- a/arch/loongarch/include/asm/fixmap.h
>> >> +++ b/arch/loongarch/include/asm/fixmap.h
>> >> @@ -12,7 +12,9 @@
>> >>
>> >>  enum fixed_addresses {
>> >>         FIX_HOLE,
>> >> +#ifdef CONFIG_FIX_EARLYCON_MEM
>> >>         FIX_EARLYCON_MEM_BASE,
>> >> +#endif
>> >>         __end_of_fixed_addresses
>> >>  };
>> >>
>> >>
>> >> ---
>> >> base-commit: 8155b4ef3466f0e289e8fcc9e6e62f3f4dceeac2
>> >> change-id: 20250102-la-earlycon-fixed-map-d6a48bd5b831
>> >>
>> >> Best regards,
>> >> --
>> >> Jiaxun Yang <jiaxun.yang@...goat.com>
>> >>
>>
>> --
>> - Jiaxun

-- 
- Jiaxun