linux-kernel - Re: [PATCH v2 1/6] resource: Extend the PPC32 reserved memory hack

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Date:   Tue, 23 Jan 2018 23:58:06 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Jonathan Neuschäfer <j.neuschaefer@....net>,
        linux-kernel@...r.kernel.org
Cc:     Tom Lendacky <thomas.lendacky@....com>,
        Brijesh Singh <brijesh.singh@....com>,
        devicetree@...r.kernel.org,
        Albert Herranz <albert_herranz@...oo.es>,
        Jonathan Neuschäfer <j.neuschaefer@....net>,
        linux-gpio@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...e.de>, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 1/6] resource: Extend the PPC32 reserved memory hack

Jonathan Neuschäfer <j.neuschaefer@....net> writes:

> On the Nintendo Wii, there are two ranges of physical memory, and MMIO
> in between, but Linux on ppc32 doesn't support discontiguous memory.
> Therefore a hack was introduced in commit c5df7f775148 ("powerpc: allow
> ioremap within reserved memory regions") and commit de32400dd26e ("wii:
> use both mem1 and mem2 as ram"):
>
>  - Treat the area from the start of the first memory area (MEM1) to the
>    end of the second (MEM2) as one big memory area, but mark the part
>    that doesn't belong to MEM1 or MEM2 as reserved.
>  - Only on the Wii, allow ioremap to be used on reserved memory.
>
> This hack, however, doesn't account for the "resource"-based API in
> kernel/resource.c, because __request_region performs its own checks.
>
> Extend the hack to kernel/resource.c, to allow more drivers to allocate
> their MMIO regions on the Wii.

Hi Jonathan,

Sorry but I can't merge a hack like this in generic code.

Has anyone looked at adding proper discontig mem support to PPC32?

Or can we punch a hole in the resource in the right place? Maybe from
add_system_ram_resources() ?

cheers