linux-kernel - Re: [PATCH 0/6] DISCONTIGMEM support for PPC32

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Message-ID: <20180221144240.pfu2run3pixt3pzo@latitude>
Date:   Wed, 21 Feb 2018 15:42:40 +0100
From:   Jonathan Neuschäfer <j.neuschaefer@....net>
To:     Christophe LEROY <christophe.leroy@....fr>
Cc:     Jonathan Neuschäfer <j.neuschaefer@....net>,
        linuxppc-dev@...ts.ozlabs.org, Joel Stanley <joel@....id.au>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 0/6] DISCONTIGMEM support for PPC32

Hi,

On Wed, Feb 21, 2018 at 08:06:10AM +0100, Christophe LEROY wrote:
> 
> 
> Le 20/02/2018 à 17:14, Jonathan Neuschäfer a écrit :
> > This patchset adds support for DISCONTIGMEM on 32-bit PowerPC. This is
> > required to properly support the Nintendo Wii's memory layout, in which
> > there are two blocks of RAM and MMIO in the middle.
> > 
> > Previously, this memory layout was handled by code that joins the two
> > RAM blocks into one, reserves the MMIO hole, and permits allocations of
> > reserved memory in ioremap. This hack didn't work with resource-based
> > allocation (as used for example in the GPIO driver for Wii[1]), however.
> > 
> > After this patchset, users of the Wii can either select CONFIG_FLATMEM
> > to get the old behaviour, or CONFIG_DISCONTIGMEM to get the new
> > behaviour.
> 
> My question might me stupid, as I don't know PCC64 in deep, but when looking
> at page_is_ram() in arch/powerpc/mm/mem.c, I have the feeling the PPC64
> implements ram by blocks. Isn't it what you are trying to achieve ? Wouldn't
> it be feasible to map to what's done in PPC64 for PPC32 ?

Using page_is_ram in __ioremap_caller and the same memblock-based
approach that's used on PPC64 on PPC32 *should* work, but I think due to
the following line in initmem_init, it won't:

	memblock_set_node(0, (phys_addr_t)ULLONG_MAX, &memblock.memory, 0);


Thanks,
Jonathan Neuschäfer

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