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Date: Mon, 30 Aug 2021 16:51:48 +1000
From: Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [RFC PATCH 4/6] powerpc/64s: Make hash MMU code build configurable
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
 linuxppc-dev@lists.ozlabs.org
References: <20210827163410.1177154-1-npiggin@gmail.com>
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Excerpts from Christophe Leroy's message of August 28, 2021 7:34 pm:
>=20
>=20
> Le 27/08/2021 =C3=A0 18:34, Nicholas Piggin a =C3=A9crit=C2=A0:
>> Introduce a new option CONFIG_PPC_64S_HASH_MMU which allows the 64s hash
>> MMU code to be compiled out if radix is selected and the minimum
>> supported CPU type is POWER9 or higher, and KVM is not selected.
>>=20
>> This saves 128kB kernel image size (90kB text) on powernv_defconfig
>> minus KVM, 350kB on pseries_defconfig minus KVM, 40kB on a tiny config.
>>=20
>> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>> ---
>=20
> ...
>=20
>> @@ -324,6 +330,7 @@ static inline void assert_pte_locked(struct mm_struc=
t *mm, unsigned long addr)
>>   }
>>   #endif /* !CONFIG_DEBUG_VM */
>>  =20
>> +#if defined(CONFIG_PPC_RADIX_MMU) && defined(CONFIG_PPC_64S_HASH_MMU)
>>   static inline bool radix_enabled(void)
>>   {
>>   	return mmu_has_feature(MMU_FTR_TYPE_RADIX);
>> @@ -333,6 +340,27 @@ static inline bool early_radix_enabled(void)
>>   {
>>   	return early_mmu_has_feature(MMU_FTR_TYPE_RADIX);
>>   }
>> +#elif defined(CONFIG_PPC_64S_HASH_MMU)
>> +static inline bool radix_enabled(void)
>> +{
>> +	return false;
>> +}
>> +
>> +static inline bool early_radix_enabled(void)
>> +{
>> +	return false;
>> +}
>> +#else
>> +static inline bool radix_enabled(void)
>> +{
>> +	return true;
>> +}
>> +
>> +static inline bool early_radix_enabled(void)
>> +{
>> +	return true;
>> +}
>> +#endif
>=20
> You don't need something that complex. You don't need to change that at a=
ll indeed, just have to=20
> ensure that when CONFIG_PPC_64S_HASH_MMU is not selected you have MMU_FTR=
_TYPE_RADIX included in=20
> MMU_FTRS_ALWAYS and voila.

Yeah I had that as a later patch that fixes up the MMU ftrs for 64s=20
which does that, I think was required before some of your patches were=20
upstreamed.

But looks like it is now trivial so I should just pull that in here.

Thanks,
Nick