[PATCH] [RFT] drm/i915: Ensure a context is loaded before RC6

[Ben Widawsky <benjamin.widawsky@intel.com>]

RC6 works a lot like HW contexts in that when the GPU enters RC6 it
saves away the state to a context, and loads it upon wake.

It's to be somewhat expected that BIOS will not set up valid GPU state.
As a result, if loading bad state can cause the GPU to get angry, it
would make sense then that we need to load state first. There are two
ways in which we can do this:

1. Create 3d state in the driver, load it up, then enable RC6.
1b. Reuse a known good state, and just bind objects where needed. Then
enable RC6
2. Hold off enabling RC6 until userspace has had a chance to complete
batches.

This patch is a bad hack. It suffers two flaws. The first is, if the
driver is loaded, but a batch is not submitted/completed, we'll never
enter rc6. The other is, it expects userspace to submit a batch with 3d
state first. Both of these things are not actual flaws for most users.

Technically, this tactic is required for all platforms, though I am not
certain we've seen real failures.

Cc: David E. Box <david.e.box@intel.com>
Cc: Kristen Carlson Accardi <kristen@linux.intel.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
---
 drivers/gpu/drm/i915/i915_gem.c      | 6 ++++++
 drivers/gpu/drm/i915/intel_display.c | 4 ----
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 08331e1..83847fc 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2482,6 +2482,7 @@ void i915_gem_reset(struct drm_device *dev)
 void
 i915_gem_retire_requests_ring(struct intel_ring_buffer *ring)
 {
+	static bool rc6_enabled = false;
 	uint32_t seqno;
 
 	if (list_empty(&ring->request_list))
@@ -2505,6 +2506,11 @@ i915_gem_retire_requests_ring(struct intel_ring_buffer *ring)
 		if (!i915_seqno_passed(seqno, obj->last_read_seqno))
 			break;
 
+		if (unlikely(!rc6_enabled) && ring->id == RCS) {
+			intel_enable_gt_powersave(ring->dev);
+			rc6_enabled = true;
+		}
+
 		i915_gem_object_move_to_inactive(obj);
 	}
 
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 4d4a0d9..990819a 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -10982,10 +10982,6 @@ void intel_modeset_init_hw(struct drm_device *dev)
 	intel_init_clock_gating(dev);
 
 	intel_reset_dpio(dev);
-
-	mutex_lock(&dev->struct_mutex);
-	intel_enable_gt_powersave(dev);
-	mutex_unlock(&dev->struct_mutex);
 }
 
 void intel_modeset_suspend_hw(struct drm_device *dev)
-- 
1.8.5.3