[RFC 2/2] drm/i915: Remove PAT hack from i915_gem_object_can_bypass_llc

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

According to the comment in i915_gem_object_can_bypass_llc the purpose of
the function is to return false if the platform/object has a caching mode
where GPU can bypass the LLC.

So far the only platforms which allegedly can do this are Jasperlake and
Elkhartlake, and that via MOCS (not PAT).

Instead of blindly assuming that objects where userspace has set the PAT
index can (bypass the LLC), question is is there a such PAT index on a
platform. Probably starting with Meteorlake since that one is the only one
where set PAT extension can be currently used. Or if there is a MOCS entry
which can achieve the same thing on Meteorlake.

If there is such PAT, now that i915 can be made to understand them better,
we can make the check more fine grained. Or if there is a MOCS entry then
we probably should apply the blanket IS_METEORLAKE condition.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Fixes: 9275277d5324 ("drm/i915: use pat_index instead of cache_level")
Cc: Chris Wilson <chris.p.wilson at linux.intel.com>
Cc: Fei Yang <fei.yang at intel.com>
Cc: Andi Shyti <andi.shyti at linux.intel.com>
Cc: Matt Roper <matthew.d.roper at intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_object.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c
index 33a1e97d18b3..1e34171c4162 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
@@ -229,12 +229,6 @@ bool i915_gem_object_can_bypass_llc(struct drm_i915_gem_object *obj)
 	if (!(obj->flags & I915_BO_ALLOC_USER))
 		return false;
 
-	/*
-	 * Always flush cache for UMD objects at creation time.
-	 */
-	if (obj->pat_set_by_user)
-		return true;
-
 	/*
 	 * EHL and JSL add the 'Bypass LLC' MOCS entry, which should make it
 	 * possible for userspace to bypass the GTT caching bits set by the
-- 
2.39.2