linux-kernel - Re: [PATCH 1/7] mips: dmi: Fix early remap on MIPS32

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Message-Id: <b996b542-4cd3-4f9d-b221-00b2d5ef224e@app.fastmail.com>
Date:   Wed, 22 Nov 2023 20:35:01 +0100
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Serge Semin" <fancer.lancer@...il.com>,
        "Thomas Bogendoerfer" <tsbogend@...ha.franken.de>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        "Mike Rapoport" <rppt@...nel.org>,
        "Matthew Wilcox" <willy@...radead.org>,
        "Tiezhu Yang" <yangtiezhu@...ngson.cn>,
        "Huacai Chen" <chenhuacai@...nel.org>,
        "Yinglu Yang" <yangyinglu@...ngson.cn>,
        "Jiaxun Yang" <jiaxun.yang@...goat.com>
Cc:     "Alexey Malahov" <Alexey.Malahov@...kalelectronics.ru>,
        "Aleksandar Rikalo" <aleksandar.rikalo@...mia.com>,
        "Aleksandar Rikalo" <arikalo@...il.com>,
        "Dragan Mladjenovic" <dragan.mladjenovic@...mia.com>,
        "Chao-ying Fu" <cfu@...ecomp.com>, "Marc Zyngier" <maz@...nel.org>,
        linux-mips@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] mips: dmi: Fix early remap on MIPS32

On Wed, Nov 22, 2023, at 19:23, Serge Semin wrote:
> dmi_early_remap() has been defined as ioremap_cache() which on MIPS32 gets
> to be converted to the VM-based mapping. DMI early remapping is performed
> at the setup_arch() stage with no VM available. So calling the
> dmi_early_remap() for MIPS32 causes the system to crash at the early boot
> time. Fix that by converting dmi_early_remap() to the uncached remapping
> which is always available on both 32 and 64-bits MIPS systems.
>
> Fixes: be8fa1cb444c ("MIPS: Add support for Desktop Management Interface (DMI)")
> Signed-off-by: Serge Semin <fancer.lancer@...il.com>
> ---
>  arch/mips/include/asm/dmi.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/mips/include/asm/dmi.h b/arch/mips/include/asm/dmi.h
> index 27415a288adf..525aad1572d1 100644
> --- a/arch/mips/include/asm/dmi.h
> +++ b/arch/mips/include/asm/dmi.h
> @@ -5,7 +5,7 @@
>  #include <linux/io.h>
>  #include <linux/memblock.h>
> 
> -#define dmi_early_remap(x, l)		ioremap_cache(x, l)
> +#define dmi_early_remap(x, l)		ioremap_uc(x, l)

Please don't use ioremap_uc() in new code, we are in the (long)
process of removing it from the kernel for everything except
x86-32, and it already returns NULL on most of them.

Would the normal ioremap() work for you here? It seems to
do the same thing as ioremap_uc() on mips and a couple of 
other architectures that have not yet killed it off.

   Arnd