Patch "drm/i915: Avoid GPU hang when coming out of s3 or s4" has been added to the 4.0-stable tree

This is a note to let you know that I've just added the patch titled

drm/i915: Avoid GPU hang when coming out of s3 or s4

to the 4.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     drm-i915-avoid-gpu-hang-when-coming-out-of-s3-or-s4.patch

and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Peter Antoine <[email protected]>
Date: Mon, 11 May 2015 08:50:45 +0100
Subject: drm/i915: Avoid GPU hang when coming out of s3 or s4

From: Peter Antoine <[email protected]>

commit 364aece01a2dd748fc36a1e8bf52ef639b0857bd upstream.

This patch fixes a timing issue that causes a GPU hang when 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 <[email protected]> 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

---
 drivers/gpu/drm/i915/i915_drv.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

@@ -693,6 +693,16 @@ static int i915_drm_resume(struct drm_de
 		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. i915_gem_init_hw() will initiate
+		 * batches to update/restore the context.
+		 *
+		 * Modeset enabling in intel_modeset_init_hw() also needs
+		 * working interrupts.
+		 */
+		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");

@@ -700,9 +710,6 @@ static int i915_drm_resume(struct drm_de
 		}
 		mutex_unlock(&dev->struct_mutex);
 
-		/* We need working interrupts for modeset enabling ... */
-		intel_runtime_pm_enable_interrupts(dev_priv);
-
 		intel_modeset_init_hw(dev);
 
 		spin_lock_irq(&dev_priv->irq_lock);

Patches currently in stable-queue which might be from [email protected] are

queue-4.0/drm-i915-avoid-gpu-hang-when-coming-out-of-s3-or-s4.patch