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

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Message-ID: <20220609222420.ponpoodiqmaqtwht@pali>
Date:   Fri, 10 Jun 2022 00:24:20 +0200
From:   Pali Rohár <pali@...nel.org>
To:     linux-mm@...ck.org
Cc:     Ash Logan <ash@...quark.com>, 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 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?

> 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@...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
> > >>>>