From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Thu, 20 Apr 2017 11:17:09 +0100
Subject: drm/i915: Use discardable buffers for rings
Git-commit: 2d6c4c84230df9ff99b626b52b11049e449632c9
Patch-mainline: v4.13-rc1
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

The contents of a ring are only valid between HEAD and TAIL, when the
ring is idle (HEAD == TAIL) we can simply let the pages go under memory
pressure if they are not pinned by an active context. Any new content
will be written after HEAD and so the ring will again be valid between
HEAD and TAIL, everything outside can be discarded.

Note that we take care of ensuring that we do not reset the HEAD
backwards following a GPU hang on an idle ring.

The same precautions are what enable us to use stolen memory for rings.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170420101709.27250-1-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1353,7 +1353,7 @@ intel_ring_create_vma(struct drm_i915_pr
 
 	obj = i915_gem_object_create_stolen(dev_priv, size);
 	if (!obj)
-		obj = i915_gem_object_create(dev_priv, size);
+		obj = i915_gem_object_create_internal(dev_priv, size);
 	if (IS_ERR(obj))
 		return ERR_CAST(obj);