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Date: Fri, 22 Oct 2021 19:30:13 +1000
From: Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH v3 15/18] powerpc/64s: Make hash MMU support configurable
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
 linuxppc-dev@lists.ozlabs.org
References: <20211021223013.2641952-1-npiggin@gmail.com>
 <20211021223013.2641952-16-npiggin@gmail.com>
 <7e10f779-e968-e723-cdbc-4510acdf64a8@csgroup.eu>
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Excerpts from Christophe Leroy's message of October 22, 2021 5:02 pm:
>=20
>=20
> Le 22/10/2021 =C3=A0 00:30, Nicholas Piggin a =C3=A9crit=C2=A0:
>> This adds Kconfig selection which allows 64s hash MMU support to be
>> disabled. It can be disabled if radix support is enabled, the minimum
>> supported CPU type is POWER9 (or higher), and KVM is not selected.
>>=20
>> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>> ---
>>   arch/powerpc/Kconfig                     |  3 ++-
>>   arch/powerpc/include/asm/mmu.h           | 16 ++++++++++---
>>   arch/powerpc/kernel/dt_cpu_ftrs.c        | 14 ++++++++----
>>   arch/powerpc/kvm/Kconfig                 |  1 +
>>   arch/powerpc/mm/init_64.c                | 15 +++++++++---
>>   arch/powerpc/platforms/Kconfig.cputype   | 29 ++++++++++++++++++++++--
>>   arch/powerpc/platforms/cell/Kconfig      |  1 +
>>   arch/powerpc/platforms/maple/Kconfig     |  1 +
>>   arch/powerpc/platforms/microwatt/Kconfig |  2 +-
>>   arch/powerpc/platforms/pasemi/Kconfig    |  1 +
>>   arch/powerpc/platforms/powermac/Kconfig  |  1 +
>>   arch/powerpc/platforms/powernv/Kconfig   |  2 +-
>>   12 files changed, 71 insertions(+), 15 deletions(-)
>>=20
>=20
>> diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platf=
orms/Kconfig.cputype
>> index a208997ade88..1cf254a5d5d4 100644
>> --- a/arch/powerpc/platforms/Kconfig.cputype
>> +++ b/arch/powerpc/platforms/Kconfig.cputype
>=20
>> @@ -364,6 +371,17 @@ config SPE
>>  =20
>>   	  If in doubt, say Y here.
>>  =20
>> +config PPC_64S_HASH_MMU
>> +	bool "Hash MMU Support"
>> +	depends on PPC_BOOK3S_64
>> +	select PPC_MM_SLICES
>> +	default y
>> +	help
>> +	  Enable support for the Power ISA Hash style MMU. This is implemented
>> +	  by all IBM Power and other Book3S CPUs.
>> +
>> +	  If you're unsure, say Y.
>> +
>>   config PPC_RADIX_MMU
>>   	bool "Radix MMU Support"
>>   	depends on PPC_BOOK3S_64
>> @@ -374,9 +392,10 @@ config PPC_RADIX_MMU
>>   	  is only implemented by IBM Power9 CPUs, if you don't have one of th=
em
>>   	  you can probably disable this.
>>  =20
>> -config PPC_RADIX_MMU_DEFAULT
>> +config PPC_RADIX_MMU_DEFAULT_OPTION
>>   	bool "Default to using the Radix MMU when possible"
>>   	depends on PPC_RADIX_MMU
>> +	depends on PPC_64S_HASH_MMU
>>   	default y
>>   	help
>>   	  When the hardware supports the Radix MMU, default to using it unles=
s
>> @@ -387,6 +406,12 @@ config PPC_RADIX_MMU_DEFAULT
>>  =20
>>   	  If you're unsure, say Y.
>>  =20
>> +config PPC_RADIX_MMU_DEFAULT
>> +	bool
>> +	depends on PPC_BOOK3S_64
>> +	depends on PPC_RADIX_MMU_DEFAULT_OPTION || !PPC_64S_HASH_MMU
>> +	default y
>> +
>=20
> Why do you need that PPC_RADIX_MMU_DEFAULT_OPTION ?
>=20
> What about
>=20
> 	config PPC_RADIX_MMU_DEFAULT
> 		bool "Default to using the Radix MMU when possible" if PPC_64S_HASH_MMU
> 		depends on PPC_RADIX_MMU
> 		depends on PPC_BOOK3S_64
> 		default y

That's what I was trying to do I guess, I forget about the if clause on=20
the bool option.

>> diff --git a/arch/powerpc/platforms/cell/Kconfig b/arch/powerpc/platform=
s/cell/Kconfig
>> index db4465c51b56..faa894714a2a 100644
>> --- a/arch/powerpc/platforms/cell/Kconfig
>> +++ b/arch/powerpc/platforms/cell/Kconfig
>> @@ -8,6 +8,7 @@ config PPC_CELL_COMMON
>>   	select PPC_DCR_MMIO
>>   	select PPC_INDIRECT_PIO
>>   	select PPC_INDIRECT_MMIO
>> +	select PPC_64S_HASH_MMU
>=20
> Is this one (and the others) needed ?
>=20
> Because it PPC_64S_HASH_MMU is 'default y', selection shouldn't be=20
> needed I think.
>=20
> Did you check with savedefconfig ?

The platform ones maybe aren't needed but it's because the cpu type=20
support selects hash (I don't want it to be configurable even if it=20
defaults to y). But it probably makes better sense to select this with=20
CPU type support rather than platform.

Thanks,
Nick