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Date:   Mon, 8 Aug 2022 20:40:34 +0200
From:   Pali =?utf-8?B?Um9ow6Fy?= <pali@kernel.org>
To:     linux-mm@kvack.org
Cc:     Ash Logan <ash@heyquark.com>, paulus@samba.org, mpe@ellerman.id.au,
        christophe.leroy@csgroup.eu, robh+dt@kernel.org,
        benh@kernel.crashing.org, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org, j.ne@posteo.net
Subject: Re: [PATCH 11/12] powerpc: wiiu: don't enforce flat memory
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On Friday 10 June 2022 00:24:20 Pali Rohár wrote:
> On Friday 20 May 2022 14:30:02 Pali Rohár wrote:
> > + linux-mm
> > 
> > Do you know what are requirements for kernel to support non-contiguous
> > memory support and what is needed to enable it for 32-bit powerpc?
> 
> Any hints?

PING?

> > Currently powerpc arch code does not support "memblock.memory.cnt > 1"
> > except for WII which seems like a hack... See below.
> > 
> > On Friday 20 May 2022 20:44:04 Ash Logan wrote:
> > > On 20/5/22 18:04, Pali Rohár wrote:
> > > > 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?
> > > 
> > > Not that I know of, I was just saying that I was only aware of those two
> > > boards where the memory map isn't contiguous, and that is the only place
> > > where it has been tested. Evidently you know of another board!
> > > 
> > > > 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).
> > > 
> > > If it's like the Wii or Wii U (some memory at 0, a gap for MMIO or
> > > whatever, then more memory at a higher address) then you should try a
> > > patch along these lines, because barring the unknowns I mentioned before
> > > it should work. At least as far as I'm aware ;)
> > > 
> > > >>>> Signed-off-by: Ash Logan <ash@heyquark.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
> > > >>>>