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

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Message-ID: <a36983ec-5e97-e968-8143-1b2615ea55f8@c-s.fr>
Date:   Wed, 21 Feb 2018 16:02:25 +0100
From:   Christophe LEROY <christophe.leroy@....fr>
To:     Jonathan Neuschäfer <j.neuschaefer@....net>
Cc:     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



Le 21/02/2018 à 15:42, Jonathan Neuschäfer a écrit :
> 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);

Can't we just fix that ?

Christophe

> 
> 
> Thanks,
> Jonathan Neuschäfer
>