[PATCH v3 6/8] drm/xe: Force flush system memory AuxCCS framebuffers before scan out

[Tvrtko Ursulin]

Even though frame buffer objects are created as write-combined, in
practice, on top of all the ring buffer flushing, an additional clflush
seems to be needed before display engine can coherently scan out the
AuxCCS compressed data without transient artifacts.

If for comparison we look at how i915 handles things (where AuxCCS works
fine), as it happens it has this same clflush before a frame buffer is
pinned for display for the first time, courtesy the dynamic tracking of
the buffer cache mode and setting the latter to uncached before handing
to display.

Since xe considers the buffer object caching mode as static we can
implement the same approach by adding a flag telling us if the buffer
was ever pinned for display and flush on the first pin. Subsequent re-pins
will not repeat the clflush but so far I have not observed any glitching
after the first pin.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>
---
 drivers/gpu/drm/xe/display/xe_fb_pin.c | 13 +++++++++++++
 drivers/gpu/drm/xe/xe_bo_types.h       | 14 +++++++++-----
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/xe/display/xe_fb_pin.c b/drivers/gpu/drm/xe/display/xe_fb_pin.c
index d11a003880dc..13030fd2728a 100644
--- a/drivers/gpu/drm/xe/display/xe_fb_pin.c
+++ b/drivers/gpu/drm/xe/display/xe_fb_pin.c
@@ -332,6 +332,7 @@ static struct i915_vma *__xe_pin_fb_vma(const struct intel_framebuffer *fb,
 	struct i915_vma *vma = kzalloc(sizeof(*vma), GFP_KERNEL);
 	struct drm_gem_object *obj = intel_fb_bo(&fb->base);
 	struct xe_bo *bo = gem_to_xe_bo(obj);
+	bool first_pin;
 	int ret;
 
 	if (!vma)
@@ -363,6 +364,9 @@ static struct i915_vma *__xe_pin_fb_vma(const struct intel_framebuffer *fb,
 	if (ret)
 		goto err;
 
+	first_pin = !bo->display_pin;
+	bo->display_pin = true;
+
 	if (IS_DGFX(xe))
 		ret = xe_bo_migrate(bo, XE_PL_VRAM0);
 	else
@@ -383,6 +387,15 @@ static struct i915_vma *__xe_pin_fb_vma(const struct intel_framebuffer *fb,
 
 	/* Ensure DPT writes are flushed */
 	xe_device_l2_flush(xe);
+
+	/*
+	 * Force flush frame buffer data for non-coherent display access when
+	 * AuxCCS formats are used.
+	 */
+	if (first_pin && !xe_bo_is_vram(bo) && !xe_bo_is_stolen(bo) &&
+	    intel_fb_is_ccs_modifier(fb->base.modifier))
+		drm_clflush_sg(xe_bo_sg(bo));
+
 	return vma;
 
 err_unpin:
diff --git a/drivers/gpu/drm/xe/xe_bo_types.h b/drivers/gpu/drm/xe/xe_bo_types.h
index 15a92e3d4898..b900cb290b01 100644
--- a/drivers/gpu/drm/xe/xe_bo_types.h
+++ b/drivers/gpu/drm/xe/xe_bo_types.h
@@ -68,11 +68,6 @@ struct xe_bo {
 	struct llist_node freed;
 	/** @update_index: Update index if PT BO */
 	int update_index;
-	/** @created: Whether the bo has passed initial creation */
-	bool created;
-
-	/** @ccs_cleared */
-	bool ccs_cleared;
 
 	/**
 	 * @cpu_caching: CPU caching mode. Currently only used for userspace
@@ -84,6 +79,15 @@ struct xe_bo {
 	/** @devmem_allocation: SVM device memory allocation */
 	struct drm_gpusvm_devmem devmem_allocation;
 
+	/** @created: Whether the bo has passed initial creation */
+	bool created : 1;
+
+	/** @ccs_cleared */
+	bool ccs_cleared : 1;
+
+	/** @display_pin: Was it ever pinned to display */
+	bool display_pin : 1;
+
 	/** @vram_userfault_link: Link into @mem_access.vram_userfault.list */
 		struct list_head vram_userfault_link;
 
-- 
2.48.0