[PATCH v4 3/8] drm/i915/ttm: only trust snooping for dgfx when deciding default cache_level

[Robert Beckett]

By default i915_ttm_cache_level() decides I915_CACHE_LLC if HAS_SNOOP.
This is divergent from existing backends code which only considers
HAS_LLC.
Testing shows that trusting snooping on gen5- is unreliable and bsw via
ggtt mappings, so limit DGFX for now and maintain previous behaviour.

Signed-off-by: Robert Beckett <bob.beckett at collabora.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
index 042c2237e287..a949594237d9 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
@@ -52,7 +52,9 @@ static enum i915_cache_level
 i915_ttm_cache_level(struct drm_i915_private *i915, struct ttm_resource *res,
 		     struct ttm_tt *ttm)
 {
-	return ((HAS_LLC(i915) || HAS_SNOOP(i915)) &&
+	bool can_snoop = HAS_SNOOP(i915) && IS_DGFX(i915);
+
+	return ((HAS_LLC(i915) || can_snoop) &&
 		!i915_ttm_gtt_binds_lmem(res) &&
 		ttm->caching == ttm_cached) ? I915_CACHE_LLC :
 		I915_CACHE_NONE;
-- 
2.25.1