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

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Date:   Fri, 20 May 2022 13:41:04 +1000
From:   Ash Logan <ash@...quark.com>
To:     Pali Rohár <pali@...nel.org>
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 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.

>> 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
>>