Re: [RFC PATCH 7/8] mm/ioremap: Consider IOREMAP space in generic ioremap

[Arnd Bergmann]

On Mon, Oct 17, 2022, at 2:50 PM, Michael Ellerman wrote:
> "Arnd Bergmann" <arnd@xxxxxxxx> writes:
>>
>> My guess is that there was no technical reason for this, other
>> than having no reason to change the behavior at the time.
>
> I think the immediate reason for it is that on some CPUs we have to use
> 4K pages in the HPT for IO mappings, but PAGE_SIZE == 64K, and we can
> only have a single page size per segment (256M or 1T).

Right, makes sense. Both the original patch, or the variant with
defining IOREMAP_START everywhere seem fine to me then.

     Arnd