[PATCH] drm/i915/selftests: keep same cache settings as timeline

[fei.yang at intel.com]

From: Fei Yang <fei.yang at intel.com>

On MTL, objects allocated through i915_gem_object_create_internal() are
mapped as uncached in GPU by default because HAS_LLC is false. However
in the live_hwsp_read selftest these watcher objects are mapped as WB
on CPU side. The conseqence is that the updates done by the GPU are not
immediately visible to CPU, thus the selftest is randomly failing due to
the stale data in CPU cache. Solution can be either setting WC for CPU +
UC for GPU, or WB for CPU + 1-way coherent WB for GPU.
To keep the consistency, let's simply inherit the same cache settings
from the timeline, which is WB for CPU + 1-way coherent WB for GPU,
because this test is supposed to emulate the behavior of the timeline
anyway.

v2: copy cache settings from timeline instead of setting it to WC
    (Suggested by Chris)

Signed-off-by: Fei Yang <fei.yang at intel.com>
Reviewed-by: Chris Wilson <chris.p.wilson at linux.intel.com>
Acked-by: Jonathan Cavitt <jonathan.cavitt at intel.com>
Acked-by: Matt Roper <matthew.d.roper at intel.com>
---
 drivers/gpu/drm/i915/gt/selftest_timeline.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/selftest_timeline.c b/drivers/gpu/drm/i915/gt/selftest_timeline.c
index 522d0190509c..631aaed9bc3d 100644
--- a/drivers/gpu/drm/i915/gt/selftest_timeline.c
+++ b/drivers/gpu/drm/i915/gt/selftest_timeline.c
@@ -825,7 +825,8 @@ static bool cmp_gte(u32 a, u32 b)
 	return a >= b;
 }
 
-static int setup_watcher(struct hwsp_watcher *w, struct intel_gt *gt)
+static int setup_watcher(struct hwsp_watcher *w, struct intel_gt *gt,
+			 struct intel_timeline *tl)
 {
 	struct drm_i915_gem_object *obj;
 	struct i915_vma *vma;
@@ -834,7 +835,10 @@ static int setup_watcher(struct hwsp_watcher *w, struct intel_gt *gt)
 	if (IS_ERR(obj))
 		return PTR_ERR(obj);
 
-	w->map = i915_gem_object_pin_map_unlocked(obj, I915_MAP_WB);
+	/* keep the same cache settings as timeline */
+	i915_gem_object_set_cache_coherency(obj, tl->hwsp_ggtt->obj->cache_level);
+	w->map = i915_gem_object_pin_map_unlocked(obj,
+			page_unmask_bits(tl->hwsp_ggtt->obj->mm.mapping));
 	if (IS_ERR(w->map)) {
 		i915_gem_object_put(obj);
 		return PTR_ERR(w->map);
@@ -1004,8 +1008,10 @@ static int live_hwsp_read(void *arg)
 	if (!tl->has_initial_breadcrumb)
 		goto out_free;
 
+	selftest_tl_pin(tl);
+
 	for (i = 0; i < ARRAY_SIZE(watcher); i++) {
-		err = setup_watcher(&watcher[i], gt);
+		err = setup_watcher(&watcher[i], gt, tl);
 		if (err)
 			goto out;
 	}
@@ -1160,6 +1166,8 @@ static int live_hwsp_read(void *arg)
 	for (i = 0; i < ARRAY_SIZE(watcher); i++)
 		cleanup_watcher(&watcher[i]);
 
+	intel_timeline_unpin(tl);
+
 	if (igt_flush_test(gt->i915))
 		err = -EIO;
 
-- 
2.25.1