svn commit: r327950 - in head/sys/powerpc: aim include powerpc ps3

[Nathan Whitehorn]

On 01/14/18 09:52, Konstantin Belousov wrote:
> On Sun, Jan 14, 2018 at 09:30:53AM -0800, Nathan Whitehorn wrote:
>> The immediate consequence of that is that no MI code that knows about
>> direct maps can possibly take advantage of the direct map on this
>> platform. Do we really want that to save some conditional logic that
>> would get optimized out on amd64 and arm64 anyway? I really do not see
>> the benefit here.
> It is not clear what do you mean.  Are you saying that there is no benefit
> of providing the conditional logic, or that it is not benefit of exclusing
> powerpc ?

Sorry, that was poorly stated. Let me try again:

If we make a PPC_PHYS_TO_DMAP(), but there is an MI PHYS_TO_DMAP() API, 
consumer code in the MI parts of the kernel won't be able to benefit 
from the PPC direct map, which seems unfortunate. The cost from a code 
perspective of having an if (direct_map_available) seems low, since on 
systems where direct_map_available is defined to be 1, the compiler will 
optimize it to the same code as if gated by #ifdef. It might be more 
cumbersome to write the code, however.

> I do not object against adding the conditional, but it should not be
> too clumsy to use.
>

OK. Let me try to draft something in the next couple days and see how 
much of a pain it is in practice.
-Nathan