The Vulkan driver in Mesa for Intel hardware never uses relocations if
it's running on a version of i915 that supports at least softpin which
all versions of i915 supporting Gen12 do.  On the OpenGL side, Gen12+ is
only supported by iris which never uses relocations.  The older i965
driver in Mesa does use relocations but it only supports Intel hardware
through Gen11 and has been deprecated for all hardware Gen9+.  The
compute driver also never uses relocations.  This only leaves the media
driver which is supposed to be switching to softpin going forward.
Making softpin a requirement for all future hardware seems reasonable.

There is one piece of hardware enabled by default in i915: RKL which was
enabled by e22fa6f0 which has not yet landed in drm-next so this
almost but not really a userspace API change for RKL.  If it becomes a
problem, we can always add !IS_ROCKETLAKE(eb->i915) to the condition.

Rejecting relocations starting with newer Gen12 platforms has the
benefit that we don't have to bother supporting it on platforms with
local memory.  Given how much CPU touching of memory is required for
relocations, not having to do so on platforms where not all memory is
directly CPU-accessible carries significant advantages.

v2 (Jason Ekstrand):
 - Allow TGL-LP platforms as they've already shipped

v3 (Jason Ekstrand):
 - WARN_ON platforms with LMEM support in case the check is wrong

v4 (Jason Ekstrand):
 - Call out Rocket Lake in the commit message

v5 (Jason Ekstrand):
 - Drop the HAS_LMEM check as it's already covered by the version check

v6 (Jason Ekstrand):
 - Move the check to eb_validate_vma() with all the other exec_object
   validation checks.
Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Zbigniew Kempczyński <zbigniew.kempczynski@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210317234014.2271006-3-jason@jlekstrand.net