[Intel-gfx] [PATCH 01/20] drm/i915: "Race-to-idle" on switching to the kernel context

[Chris Wilson]

During suspend we want to flush out all active contexts and their
rendering. To do so we queue a request from the kernel's context, once
we know that request is done, we know the GPU is completely idle. To
speed up that switch bump the GPU clocks.

Switching to the kernel context prior to idling is also used to enforce
a barrier before changing OA properties, and when evicting active
rendering from the global GTT. All cases where we do want to
race-to-idle.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: David Weinehall <david.weinehall at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_gem_context.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 58a2a44f88bd..ca1423ad2708 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -895,6 +895,7 @@ int i915_gem_switch_to_kernel_context(struct drm_i915_private *dev_priv)
 
 	for_each_engine(engine, dev_priv, id) {
 		struct drm_i915_gem_request *req;
+		bool active = false;
 		int ret;
 
 		if (engine_has_kernel_context(engine))
@@ -913,13 +914,17 @@ int i915_gem_switch_to_kernel_context(struct drm_i915_private *dev_priv)
 			prev = i915_gem_active_raw(&tl->last_request,
 						   &dev_priv->drm.struct_mutex);
 			if (prev)
-				i915_sw_fence_await_sw_fence_gfp(&req->submit,
-								 &prev->submit,
-								 GFP_KERNEL);
+				active |= i915_sw_fence_await_sw_fence_gfp(&req->submit,
+									   &prev->submit,
+									   GFP_KERNEL) > 0;
 		}
 
 		ret = i915_switch_context(req);
+
+		if (active)
+			gen6_rps_boost(req, NULL);
 		i915_add_request(req);
+
 		if (ret)
 			return ret;
 	}
-- 
2.14.1