drm/i915: Flush ggtt writes through the old fenced vma before changing fences

This is a precautionary measure as I have no evidence to suggest we've
hit a bug here (I was hoping this might explain gdg's odd behaviour, but
alas), but given that we have a function to flush the ggtt writes it
seems prudent to use it prior to changing the fence register. Due to the
intrinsic nature of the GTT often operating as an independent mmio path,
we should not just rely on the write to the fence acting as a full flush
for GTT writes.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180130164457.14037-1-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_gem_fence_reg.c b/drivers/gpu/drm/i915/i915_gem_fence_reg.c
index 012250f25255fa86c47fdd3aa4480cca09b7b281..b8338d75c6f3faca71003de6b12ab25eba983562 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem_fence_reg.c
+++ b/drivers/gpu/drm/i915/i915_gem_fence_reg.c
@@ -230,10 +230,14 @@ static int fence_update(struct drm_i915_fence_reg *fence,
        }
 
        if (fence->vma) {
-               ret = i915_gem_active_retire(&fence->vma->last_fence,
-                                     &fence->vma->obj->base.dev->struct_mutex);
+               struct i915_vma *old = fence->vma;
+
+               ret = i915_gem_active_retire(&old->last_fence,
+                                            &old->obj->base.dev->struct_mutex);
                if (ret)
                        return ret;
+
+               i915_vma_flush_writes(old);
        }
 
        if (fence->vma && fence->vma != vma) {