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

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Message-ID: <CAAhV-H44VvyxHqmyQ3K8qC+HERH0FjheqAJpDCiYkQ2oK2woAg@mail.gmail.com>
Date: Fri, 3 Jan 2025 10:38:46 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Jiaxun Yang <jiaxun.yang@...goat.com>
Cc: WANG Xuerui <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

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().

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>
>