Re: [PATCH v4 2/2] RISC-V: Implement sparsemem

[Logan Gunthorpe]

On 2019-08-13 10:39 a.m., Paul Walmsley wrote:
> On Tue, 13 Aug 2019, Logan Gunthorpe wrote:
> 
>> On 2019-08-13 12:04 a.m., Greentime Hu wrote:
>>
>>> Every architecture with mmu defines their own pfn_valid().
>>
>> Not true. Arm64, for example just uses the generic implementation in
>> mmzone.h. 
> 
> arm64 seems to define their own:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/Kconfig#n899

Oh, yup. My mistake.

> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/mm/init.c#n235
> 
> While there are many architectures which have their own pfn_valid(); 
> oddly, almost none of them set HAVE_ARCH_PFN_VALID ?

Yes, much of this is super confusing. Seems HAVE_ARCH_PFN_VALID only
matters if SPARSEMEM is set. So risc-v probably doesn't need to set it
and we just need a #ifdef !CONFIG_FLATMEM around the pfn_valid
definition like other arches.

Logan