[PATCH v5] drm/i915: Avoid GPU Hang when comming out of s3 or s4

[Peter Antoine <peter.antoine@intel.com>]

This patch fixed a timing issue that causes a GPU hang when a the system
comes out of power saving.

During pm_resume, We are submitting batchbuffers before enabling
Interrupts this is causing us to miss the context switch interrupt,
and in consequence intel_execlists_handle_ctx_events is not triggered.

This patch is based on a patch from Deepak S <deepak.s@intel.com>
from another platform.

The patch fixes an issue introduced by:
  commit e7778be1eab918274f79603d7c17b3ec8be77386
  drm/i915: Fix startup failure in LRC mode after recent init changes

The above patch added a call to init_context() to fix an issue introduced
by a previous patch. But, it then opened up a small timing window for the
batches being added by the init_context (basically setting up the context)
to complete before the interrupts have been turned on, thus hanging the
GPU.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89600
Cc: stable@vger.kernel.org
Signed-off-by: Peter Antoine <peter.antoine@intel.com>
---
 drivers/gpu/drm/i915/i915_drv.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 6bb6c47..748ab13 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -734,6 +734,13 @@ static int i915_drm_resume(struct drm_device *dev)
 	intel_init_pch_refclk(dev);
 	drm_mode_config_reset(dev);
 
+	/* 
+	 * Interrupts have to be enabled before any batches are run. If not the
+	 * GPU will hang. The init_hw will initiate batches to update/restore
+	 * the context.
+	 */
+	intel_runtime_pm_enable_interrupts(dev_priv);
+
 	mutex_lock(&dev->struct_mutex);
 	if (i915_gem_init_hw(dev)) {
 		DRM_ERROR("failed to re-initialize GPU, declaring wedged!\n");
@@ -741,9 +748,7 @@ static int i915_drm_resume(struct drm_device *dev)
 	}
 	mutex_unlock(&dev->struct_mutex);
 
-	/* We need working interrupts for modeset enabling ... */
-	intel_runtime_pm_enable_interrupts(dev_priv);
-
+	/* This must follow the pm enable interrupts */
 	intel_modeset_init_hw(dev);
 
 	spin_lock_irq(&dev_priv->irq_lock);
-- 
1.9.1