[PATCH] drm/i915: Re-enable rc6 w/fix

[Ben Widawsky <ben@bwidawsk.net>]

This fixes a race condition with MI_SET_CONTEXT and setting of the
PWRCTXA register. If PWRCTXA ends up getting set before MI_SET_CONTEXT
completes, it's possible that the system will enter rc6, and try to
return to the default render context, which if unset, could cause a GPU
hang

Resolve https://bugzilla.kernel.org/show_bug.cgi?id=28582

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
---
 drivers/gpu/drm/i915/i915_drv.c      |    2 +-
 drivers/gpu/drm/i915/intel_display.c |   11 +++++++----
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 22ec066..e3c808d 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -49,7 +49,7 @@ module_param_named(powersave, i915_powersave, int, 0600);
 unsigned int i915_semaphores = 0;
 module_param_named(semaphores, i915_semaphores, int, 0600);
 
-unsigned int i915_enable_rc6 = 0;
+unsigned int i915_enable_rc6 = 1;
 module_param_named(i915_enable_rc6, i915_enable_rc6, int, 0600);
 
 unsigned int i915_lvds_downclock = 0;
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 49fb54f..5675610 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -6616,7 +6616,7 @@ void ironlake_enable_rc6(struct drm_device *dev)
 	 * GPU can automatically power down the render unit if given a page
 	 * to save state.
 	 */
-	ret = BEGIN_LP_RING(6);
+	ret = BEGIN_LP_RING(10);
 	if (ret) {
 		ironlake_teardown_rc6(dev);
 		return;
@@ -6630,12 +6630,15 @@ void ironlake_enable_rc6(struct drm_device *dev)
 		 MI_RESTORE_EXT_STATE_EN |
 		 MI_RESTORE_INHIBIT);
 	OUT_RING(MI_SUSPEND_FLUSH);
-	OUT_RING(MI_NOOP);
 	OUT_RING(MI_FLUSH);
+	OUT_RING(MI_LOAD_REGISTER_IMM(2));
+	OUT_RING(PWRCTXA);
+	OUT_RING(dev_priv->pwrctx->gtt_offset | PWRCTX_EN);
+	OUT_RING(RSTDBYCTL);
+	OUT_RING(I915_READ(RSTDBYCTL) & ~RCX_SW_EXIT);
 	ADVANCE_LP_RING();
 
-	I915_WRITE(PWRCTXA, dev_priv->pwrctx->gtt_offset | PWRCTX_EN);
-	I915_WRITE(RSTDBYCTL, I915_READ(RSTDBYCTL) & ~RCX_SW_EXIT);
+	DRM_DEBUG_DRIVER("pwrctx offset: %p", dev_priv->pwrctx->gtt_offset);
 }
 
 
-- 
1.7.3.4