[igt-dev] [RFC PATCH 1/4] lib/i915/gem_mman: add mmap_offset support

[Chris Wilson]

Quoting Joonas Lahtinen (2019-08-14 14:19:12)
> This logic shouldn't be needed either, if we have mmap_offset, we'll
> have WC support. What this logic checks is if default placed object will
> support WC mmap, which is very different from what this function
> originally did.

Fwiw, that's not always true. Once you know which ioctl you have,
you need to query the WC flags to verify the processor supports WC
access. With Xen even recent processors may be lacking a few essentials.
-Chris