linux-kernel - [PATCH v11 03/10] drm/i915/ttm: only trust snooping for dgfx when deciding default cache

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Date:   Wed, 13 Jul 2022 14:50:15 +0100
From:   Robert Beckett <bob.beckett@...labora.com>
To:     dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     kernel@...labora.com, Robert Beckett <bob.beckett@...labora.com>,
        Matthew Auld <matthew.auld@...el.com>,
        Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>, linux-kernel@...r.kernel.org
Subject: [PATCH v11 03/10] drm/i915/ttm: only trust snooping for dgfx when deciding default cache_level

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@...labora.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@...ux.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