From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
On Meteorlake CPU cache will not contain stale data after GPU access since
write-invalidate protocol is used, which means there is no need to flush
before potentially transitioning the buffer to a non-coherent domain.
Use the opportunity to documet the situation on discrete too.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Cc: Matt Roper <matthew.d.roper@xxxxxxxxx>
Cc: Fei Yang <fei.yang@xxxxxxxxx>
Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/gem/i915_gem_domain.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_domain.c b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
index ffddec1d2a76..57db9c581bf6 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_domain.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
@@ -24,9 +24,22 @@ static bool gpu_write_needs_clflush(struct drm_i915_gem_object *obj)
{
struct drm_i915_private *i915 = to_i915(obj->base.dev);
+ /*
+ * Discrete GPUs never dirty the CPU cache.
+ */
if (IS_DGFX(i915))
return false;
+ /*
+ * Cache snooping on Meteorlake is using write-invalidate so GPU writes
+ * never end up in the CPU cache.
+ *
+ * QQQ: Do other snooping platforms behave identicaly and could we
+ * therefore write this as "if !HAS_LLC(i915) && HAS_SNOOP(i915)"?
+ */
+ if (IS_METEORLAKE(i915))
+ return false;
+
/*
* For objects created by userspace through GEM_CREATE with pat_index
* set by set_pat extension, i915_gem_object_has_cache_level() will
--
2.39.2
