linux-kernel - Re: [RFC] Upstreaming Linux for Nintendo Wii U

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Message-ID: <41c696de-0e04-61e1-610c-73e9440c5c19@csgroup.eu>
Date:   Fri, 11 Feb 2022 13:11:41 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Ash Logan <ash@...quark.com>,
        "benh@...nel.crashing.org" <benh@...nel.crashing.org>,
        "paulus@...ba.org" <paulus@...ba.org>
CC:     "linkmauve@...kmauve.fr" <linkmauve@...kmauve.fr>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "amd-gfx@...ts.freedesktop.org" <amd-gfx@...ts.freedesktop.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "j.ne@...teo.net" <j.ne@...teo.net>
Subject: Re: [RFC] Upstreaming Linux for Nintendo Wii U

Hi Ash,

Le 11/02/2022 à 12:29, Michael Ellerman a écrit :
> Ash Logan <ash@...quark.com> writes:
>> - Like the Wii before it, the Wii U has a small amount of RAM at address
>> zero, a gap, then a large amount of RAM at a higher address. Instead of
>> the "map everything and reserve the gap" approach of the Wii, we loop
>> over each memblock and map only true RAM[9]. This seems to work, but as
>> far as I can tell is unique amongst powerpc32 platforms, so it's worth
>> pointing out. (Note: I've been told this doesn't work anymore after some
>> KUAP changes[10], so this point might be moot; haven't investigated)
> 
> We'd need more detail on that I guess. Currently all the 32-bit
> platforms use the flat memory model, which assumes RAM is a single
> contiguous block. Though that doesn't mean it all has to be used or
> mapped, like the Wii does. To properly support your layout you should be
> using sparsemem, but it's possible that's more trouble than it's worth,
> I'm not sure. How far apart are the low and high blocks of RAM, and what
> are their sizes?

Can you provide details on what's happening with KUAP changes ?

You are pointing to series https://lkml.org/lkml/2021/6/3/204

Does it work when CONFIG_PPC_KUAP is not selected or doesn't it work 
either ?

Are you able to bisect which commit of that series is the culprit ?

Thanks
Christophe