linux-kernel - [PATCH v2] drm/i915: Flush untouched framebuffers before display on !llc

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Message-Id: <20170109111932.6342-1-chris@chris-wilson.co.uk>
Date:   Mon,  9 Jan 2017 11:19:32 +0000
From:   Chris Wilson <chris@...is-wilson.co.uk>
To:     linux-kernel@...r.kernel.org
Cc:     intel-gfx@...ts.freedesktop.org, lkml@...garu.com,
        Chris Wilson <chris@...is-wilson.co.uk>,
        "# v4 . 10-rc1+" <drm-intel-fixes@...ts.freedesktop.org>
Subject: [PATCH v2] drm/i915: Flush untouched framebuffers before display on !llc

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@...is-wilson.co.uk>
Cc: <drm-intel-fixes@...ts.freedesktop.org> # v4.10-rc1+
---
 drivers/gpu/drm/i915/i915_gem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 76689b59fc90..bdb113ef8cfe 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3514,7 +3514,7 @@ 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