Re: [PATCH 3/4] ARM: remove support for highmem on VIVT

["Arnd Bergmann" <arnd@arndb.de>]

On Fri, Dec 19, 2025, at 18:14, Jason Gunthorpe wrote:
> On Fri, Dec 19, 2025 at 05:15:58PM +0100, Arnd Bergmann wrote:
>>  arch/arm/Kconfig                    |  1 +
>>  arch/arm/configs/gemini_defconfig   |  1 -
>>  arch/arm/configs/multi_v5_defconfig |  1 -
>>  arch/arm/configs/mvebu_v5_defconfig |  1 -
>>  arch/arm/include/asm/highmem.h      | 56 ++---------------------------
>>  arch/arm/mm/cache-feroceon-l2.c     | 31 ++--------------
>>  arch/arm/mm/cache-xsc3l2.c          | 47 +++---------------------
>>  arch/arm/mm/dma-mapping.c           | 12 ++-----
>>  arch/arm/mm/flush.c                 | 19 +++-------
>>  9 files changed, 16 insertions(+), 153 deletions(-)
>
> This looks great, but do you think there should be a boot time crash
> if a VIVT and HIGHMEM are enabled, just incase?

Do you mean in the common code or just for Arm?

We could use the Arm specific cache_is_vivt() macro, but it feels like
the 'dpends on !CPU_CACHE_VIVT' Kconfig check I added is both
safer and simpler.

In common code I don't see a way to detect vivt caches. There is
cpu_dcache_is_aliasing(), but that also seems to cover ARM11
processors with aliasing VIPT caches, which are otherwise fine
here.

     Arnd