[Intel-gfx] [PATCH 2/2] drm/i915: Discard the unbound list when suspending

[Chris Wilson]

The unbound tracking of objects is an optimisation to avoid costly
domain transfers whilst the system is rendering. Across suspend, the
objects will be involuntarily moved out of the GTT domain and will
require fixup upon resume. Rather than perform those clflushes for all
objects immediately upon resume, just move them out of the unbound
tracking list on suspend and lazily reload them from the CPU domain as
and when they are used afterwards.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c |   24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index f6ef53f..db14c73 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3912,6 +3912,17 @@ void i915_gem_free_object(struct drm_gem_object *gem_obj)
 	i915_gem_object_free(obj);
 }
 
+static void
+i915_gem_discard_unbound(struct drm_i915_private *dev_priv)
+{
+	struct drm_i915_gem_object *obj, *next;
+
+	list_for_each_entry_safe(obj, next,
+				 &dev_priv->mm.unbound_list,
+				 gtt_list)
+		(void)i915_gem_object_put_pages(obj);
+}
+
 int
 i915_gem_idle(struct drm_device *dev)
 {
@@ -3936,6 +3947,19 @@ i915_gem_idle(struct drm_device *dev)
 	if (!drm_core_check_feature(dev, DRIVER_MODESET))
 		i915_gem_evict_everything(dev);
 
+	/* For KMS we just want to discard the unbound list as it will
+	 * change domains when thawing - and restoring its domain upon
+	 * resume seems like a false optimisation. Also note that discarding
+	 * the unbound list will have the useful side-effect of dropping
+	 * purgeable objects which it seems pointless to restore as they are
+	 * merely a userspace cache.
+	 * However, we may still have some pinned objects (like dma-buf)
+	 * that cannot simply be discarded and will require domain
+	 * restoration upon resume.
+	 */
+	if (drm_core_check_feature(dev, DRIVER_MODESET))
+		i915_gem_discard_unbound(dev_priv);
+
 	i915_gem_reset_fences(dev);
 
 	/* Hack!  Don't let anybody do execbuf while we don't control the chip.
-- 
1.7.10.4