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

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Message-ID: <193a407d-e6b8-9e29-af47-3d401b6414a0@c-s.fr>
Date:   Wed, 21 Feb 2018 08:06:10 +0100
From:   Christophe LEROY <christophe.leroy@....fr>
To:     Jonathan Neuschäfer <j.neuschaefer@....net>,
        linuxppc-dev@...ts.ozlabs.org
Cc:     Joel Stanley <joel@....id.au>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 0/6] DISCONTIGMEM support for PPC32



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 ?

Christophe

> 
> Some parts of this patchset are probably not ideal (I'm thinking of my
> implementation of pfn_to_nid here), and will require some discussion/
> changes.
> 
> [1]: https://www.spinics.net/lists/devicetree/msg213956.html
> 
> Jonathan Neuschäfer (6):
>    powerpc/mm/32: Use pfn_valid to check if pointer is in RAM
>    powerpc: numa: Fix overshift on PPC32
>    powerpc: numa: Use the right #ifdef guards around functions
>    powerpc: numa: Restrict fake NUMA enulation to CONFIG_NUMA systems
>    powerpc: Implement DISCONTIGMEM and allow selection on PPC32
>    powerpc: wii: Don't rely on reserved memory hack if DISCONTIGMEM is
>      set
> 
>   arch/powerpc/Kconfig                     |  5 ++++-
>   arch/powerpc/include/asm/mmzone.h        | 21 +++++++++++++++++++++
>   arch/powerpc/mm/numa.c                   | 18 +++++++++++++++---
>   arch/powerpc/mm/pgtable_32.c             |  2 +-
>   arch/powerpc/platforms/embedded6xx/wii.c | 10 +++++++---
>   5 files changed, 48 insertions(+), 8 deletions(-)
>