[PATCH] powerpc/powernv/prd: Validate whether address to be mapped is part of system RAM

[Jeremy Kerr]

Hi Vasant,

> > OK. How about we just don't do that?
> 
> Yes. Hostboot will fix that. It will make sure that HBRT is loaded
> into regular memory.

Super.

> > It sounds like we're just trying to work around an invalid
> > representation of the mappings.
> 
> Its not workaround. Its additional check.

The issue is that you've added a check for stuff that the kernel doesn't
(and shouldn't) know about, and assumed that the kernel knows better
than the device tree. It may be the correct thing to do in this case,
but we can't guarantee that it's always correct.

For example, what if there is a future HBRT range that is fine to go
into NVRAM? With this change, that's not possible.

Or, what if there's a range of address-space that isn't backed by system
RAM (say, some MMIO-mapped hardware) that we want to expose to a future
HBRT implementation? This change will block that.

The kernel doesn't know what is and is not valid for a HBRT mapping, so
it has no reason to override what's specified in the device tree. We've
designed this so that the kernel provides the mechanism for mapping
pages, and not the policy of which pages can be mapped.

Regards,


Jeremy