[PATCH] drm/i915: Flush untouched framebuffers before display on !llc

[Chris Wilson]

On a non-llc system, the objects are created with .cache_level =
CACHE_NONE and so the transition to uncached for scanout is a no-op.
However, if the object was never written to, it will still be in the CPU
domain (having been zeroed out by shmemfs). Those cachelines need to be
flushed prior to display.

Reported-by: Vito Caputo
Fixes: a6a7cc4b7db6 ("drm/i915: Always flush the dirty CPU cache when pinning the scanout")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: <drm-intel-fixes@xxxxxxxxxxxxxxxxxxxxx> # v4.10-rc1+
---
 drivers/gpu/drm/i915/i915_gem.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 76689b59fc90..e64d0ea6113d 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2327,6 +2327,7 @@ static void i915_sg_trim(struct sg_table *orig_st)
 	if (sg_alloc_table(&new_st, orig_st->nents, GFP_KERNEL | __GFP_NOWARN))
 		return;
 
+	new_st->orig_nents = orig_st->orig_nents; /* XXX lies for 
 	new_sg = new_st.sgl;
 	for_each_sg(orig_st->sgl, sg, orig_st->nents, i) {
 		sg_set_page(new_sg, sg_page(sg), sg->length, 0);
@@ -3514,7 +3515,7 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
 	vma->display_alignment = max_t(u64, vma->display_alignment, alignment);
 
 	/* Treat this as an end-of-frame, like intel_user_framebuffer_dirty() */
-	if (obj->cache_dirty) {
+	if (obj->cache_dirty || obj->base.write_domain == I915_GEM_DOMAIN_CPU) {
 		i915_gem_clflush_object(obj, true);
 		intel_fb_obj_flush(obj, false, ORIGIN_DIRTYFB);
 	}
-- 
2.11.0