linux-kernel - Re: [PATCH 11/12] powerpc: wiiu: don't enforce flat memory

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Message-ID: <20220520080454.c3cqodsdbfbkmg56@pali>
Date:   Fri, 20 May 2022 10:04:54 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Ash Logan <ash@...quark.com>
Cc:     paulus@...ba.org, mpe@...erman.id.au, christophe.leroy@...roup.eu,
        robh+dt@...nel.org, benh@...nel.crashing.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        j.ne@...teo.net
Subject: Re: [PATCH 11/12] powerpc: wiiu: don't enforce flat memory

On Friday 20 May 2022 13:41:04 Ash Logan wrote:
> On 14/5/22 08:43, Pali Rohár wrote:
> > On Wednesday 02 March 2022 15:44:05 Ash Logan wrote:
> >> pgtable_32.c:mapin_ram loops over each valid memory range, which means
> >> non-contiguous memory just works.
> > 
> > Hello! Does it mean that non-contiguous memory works for any 32-bit
> > powerpc platform, and not only for wiiu? If yes, should not be
> > non-contiguous memory support enabled for all 32-bit ppc boards then?
> 
> Hi! Sorry for my delayed response. As best I can tell, it does indeed
> Just Work, but I have only been able to test on wiiu which is missing a
> lot of features other boards have (like PCI) - so it's possible there's
> still an assumption elsewhere in the kernel that I haven't hit.
> 
> As best I can tell, the Wii and Wii U are the only 32-bit powerpc boards
> out there where it's even possible to have non-contiguous memory.

What is the reason that those two boards are the **only**? Is there some
specific requirement from bootloader or hardware to "enable"
non-contiguous memory support?

I'm interested in enabling non-contiguous memory support for P2020-based
board as it has gaps in its 32-bit memory layout and which could be used
for RAM mapping when 4GB DDR3 module is plugged in (default is 2GB).

> >> Signed-off-by: Ash Logan <ash@...quark.com>
> >> ---
> >>  arch/powerpc/mm/init_32.c | 4 ++--
> >>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/arch/powerpc/mm/init_32.c b/arch/powerpc/mm/init_32.c
> >> index 3d690be48e84..59a84629d9a0 100644
> >> --- a/arch/powerpc/mm/init_32.c
> >> +++ b/arch/powerpc/mm/init_32.c
> >> @@ -125,10 +125,10 @@ void __init MMU_init(void)
> >>  	 * lowmem_end_addr is initialized below.
> >>  	 */
> >>  	if (memblock.memory.cnt > 1) {
> >> -#ifndef CONFIG_WII
> >> +#if !defined(CONFIG_WII) && !defined(CONFIG_WIIU)
> >>  		memblock_enforce_memory_limit(memblock.memory.regions[0].size);
> >>  		pr_warn("Only using first contiguous memory region\n");
> >> -#else
> >> +#elif defined(CONFIG_WII)
> >>  		wii_memory_fixups();
> >>  #endif
> >>  	}
> >> -- 
> >> 2.35.1
> >>