linux-kernel - Re: [PATCH v1 05/10] powerpc/mm: Do early ioremaps from top to bottom on PPC64 too.

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Date:   Wed, 14 Aug 2019 08:10:59 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, npiggin@...il.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 05/10] powerpc/mm: Do early ioremaps from top to bottom
 on PPC64 too.



Le 14/08/2019 à 07:55, Christoph Hellwig a écrit :
> On Tue, Aug 13, 2019 at 08:11:38PM +0000, Christophe Leroy wrote:
>> Until vmalloc system is up and running, ioremap basically
>> allocates addresses at the border of the IOREMAP area.
> 
> Note that while a few other architectures have a magic hack like powerpc
> to make ioremap work before vmalloc, the normal practice would be
> to explicitly use early_ioremap.  I guess your change is fine for now,
> but it might make sense convert powerpc to the explicit early_ioremap
> scheme as well.
> 

I've been looking into early_ioremap(), but IIUC early_ioremap() is for 
ephemeral mappings only, it expects all early mappings to be gone at the 
end of init.

PPC installs definitive early mappings (for instance for PCI). How does 
that have to be handled ?

Christophe