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

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Message-ID: <c7cuvhuu6py5vxhhvkhekv6ned5sro4a3wzzn7v45oahfw42ud@gyqmucagt5e2>
Date:   Thu, 23 Nov 2023 12:32:24 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     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>,
        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

Hi Arnd

On Wed, Nov 22, 2023 at 08:35:01PM +0100, Arnd Bergmann wrote:
> 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.

Ok. Thanks for the heads up. I'll fix the patch to be using ioremap()
in v2. ioremap_uc() is just an macro-alias of ioremap() on MIPS.

-Serge(y)

> 
>    Arnd