[PATCH] powerpc: Make PPC_64K_PAGES depend on only 44x or PPC_BOOK3S_64

[Michael Ellerman]

Scott Wood <oss at buserror.net> writes:
> On Wed, 2019-02-20 at 01:14 +1100, Michael Ellerman wrote:
>> Christophe Leroy <christophe.leroy at c-s.fr> writes:
>> 
>> > On 02/08/2019 12:34 PM, Michael Ellerman wrote:
>> > > In commit 7820856a4fcd ("powerpc/mm/book3e/64: Remove unsupported
>> > > 64Kpage size from 64bit booke") we dropped the 64K page size support
>> > > from the 64-bit nohash (Book3E) code.
>> > > 
>> > > But we didn't update the dependencies of the PPC_64K_PAGES option,
>> > > meaning a randconfig can still trigger this code and cause a build
>> > > breakage, eg:
>> > >    arch/powerpc/include/asm/nohash/64/pgtable.h:14:2: error: #error
>> > > "Page size not supported"
>> > >    arch/powerpc/include/asm/nohash/mmu-book3e.h:275:2: error: #error
>> > > Unsupported page size
>> > > 
>> > > So remove PPC_BOOK3E_64 from the dependencies. This also means we
>> > > don't need to worry about PPC_FSL_BOOK3E, because that was just trying
>> > > to prevent the PPC_BOOK3E_64=y && PPC_FSL_BOOK3E=y case.
>> > 
>> > Does it means some cleanup could be done, for instance:
>> > 
>> > arch/powerpc/include/asm/nohash/64/pgalloc.h:#ifndef CONFIG_PPC_64K_PAGES
>> > arch/powerpc/include/asm/nohash/64/pgalloc.h:#endif /* 
>> > CONFIG_PPC_64K_PAGES */
>> > arch/powerpc/include/asm/nohash/64/pgtable.h:#ifdef CONFIG_PPC_64K_PAGES
>> > arch/powerpc/include/asm/nohash/64/slice.h:#ifdef CONFIG_PPC_64K_PAGES
>> > arch/powerpc/include/asm/nohash/64/slice.h:#else /* CONFIG_PPC_64K_PAGES
>> > */
>> > arch/powerpc/include/asm/nohash/64/slice.h:#endif /* 
>> > !CONFIG_PPC_64K_PAGES */
>> > arch/powerpc/include/asm/nohash/pte-book3e.h:#ifdef CONFIG_PPC_64K_PAGES
>> > 
>> > arch/powerpc/mm/tlb_low_64e.S:#ifdef CONFIG_PPC_64K_PAGES
>> > arch/powerpc/mm/tlb_low_64e.S:#ifndef CONFIG_PPC_64K_PAGES
>> > arch/powerpc/mm/tlb_low_64e.S:#endif /* CONFIG_PPC_64K_PAGES */
>> > arch/powerpc/mm/tlb_low_64e.S:#ifdef CONFIG_PPC_64K_PAGES
>> > arch/powerpc/mm/tlb_low_64e.S:#ifdef CONFIG_PPC_64K_PAGES
>> > arch/powerpc/mm/tlb_low_64e.S:#ifndef CONFIG_PPC_64K_PAGES
>> > arch/powerpc/mm/tlb_low_64e.S:#endif /* CONFIG_PPC_64K_PAGES */
>> > arch/powerpc/mm/tlb_low_64e.S:#ifndef CONFIG_PPC_64K_PAGES
>> > arch/powerpc/mm/tlb_low_64e.S:#endif /* CONFIG_PPC_64K_PAGES */
>> > arch/powerpc/mm/tlb_low_64e.S:#ifndef CONFIG_PPC_64K_PAGES
>> > arch/powerpc/mm/tlb_low_64e.S:#ifdef CONFIG_PPC_64K_PAGES
>> 
>> Probably.
>> 
>> Some of the FSL chips do support 64K pages at least according to some
>> datasheets. I don't know what would be required to get it working, or if
>> it even works in practice.
>> 
>> So it would be nice to get 64K working on those chips, but probably no
>> one has time or motivation to do it. In which case yeah all that code
>> should be removed.
>
> The primary TLB (TLB0) on these chips only supports 4K pages.  TLB1 supports
> many different sizes but is much smaller, hardware tablewalk only loads into
> TLB0, etc.

Aha thanks. I wondered if there was some reason for it.

So that makes it sound much less interesting, meaning all that 64K page
code should go.

cheers