[Intel-gfx] [PATCH] drm/i915: fix hard-hangs while resetting the gpu on some ilks

[Daniel Vetter]

I admit up-front that this is ugly. This patch fixes fully reliable
hard-hang on my ilk when exercising the reset paths with the hangman
i-g-t tests. Both Chris Wilson and our QA couldn't reproduce this.
This regression has been introduced in

commit 1833b134454d5300d8a9d07b78876a20395f01a9
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Wed May 9 11:56:28 2012 +0100

    drm/i915: gen6_enable_rps() wants to be called after ring initialisation

specifically calling intel_modeset_init_hw instead of open-coding half
of it. After some trial and error (and figuring out the hard way that
the problem only manifests after a full reboot) I've tracked it down
to calling ironlake_enable_drps.

Now I still think that having unified hw frobbing paths between driver
load, resume and gpu reset is highly desirable, so I've opted to just
add a reset argument to disable the offending code for gpu resets. I
have no idea why it actually blows up.

Signed-Off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/i915/i915_drv.c      |    4 ++--
 drivers/gpu/drm/i915/i915_drv.h      |    2 +-
 drivers/gpu/drm/i915/intel_display.c |    9 ++++++---
 3 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 238a521..d05fe30 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -640,7 +640,7 @@ static int i915_drm_thaw(struct drm_device *dev)
 		error = i915_gem_init_hw(dev);
 		mutex_unlock(&dev->struct_mutex);
 
-		intel_modeset_init_hw(dev);
+		intel_modeset_init_hw(dev, false);
 		drm_mode_config_reset(dev);
 		drm_irq_install(dev);
 
@@ -908,7 +908,7 @@ int i915_reset(struct drm_device *dev)
 		mutex_unlock(&dev->struct_mutex);
 
 		if (drm_core_check_feature(dev, DRIVER_MODESET))
-			intel_modeset_init_hw(dev);
+			intel_modeset_init_hw(dev, true);
 
 		drm_irq_uninstall(dev);
 		drm_irq_install(dev);
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index ae4129b..04ad9c0 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1471,7 +1471,7 @@ static inline void intel_unregister_dsm_handler(void) { return; }
 #endif /* CONFIG_ACPI */
 
 /* modesetting */
-extern void intel_modeset_init_hw(struct drm_device *dev);
+extern void intel_modeset_init_hw(struct drm_device *dev, bool reset);
 extern void intel_modeset_init(struct drm_device *dev);
 extern void intel_modeset_gem_init(struct drm_device *dev);
 extern void intel_modeset_cleanup(struct drm_device *dev);
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 308e1a2..e76d12c 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -6900,14 +6900,17 @@ static void ivb_pch_pwm_override(struct drm_device *dev)
 	I915_WRITE(BLC_PWM_PCH_CTL1, BLM_PCH_PWM_ENABLE | BLM_PCH_OVERRIDE_ENABLE);
 }
 
-void intel_modeset_init_hw(struct drm_device *dev)
+void intel_modeset_init_hw(struct drm_device *dev, bool reset)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
 	intel_init_clock_gating(dev);
 
 	if (IS_IRONLAKE_M(dev)) {
-		ironlake_enable_drps(dev);
+		/* Re-enabling drps on gpu reset hard-hangs some ilks for no
+		 * apparent reason. Hence avoid it. */
+		if (!reset)
+			ironlake_enable_drps(dev);
 		ironlake_enable_rc6(dev);
 		intel_init_emon(dev);
 	}
@@ -6979,7 +6982,7 @@ void intel_modeset_init(struct drm_device *dev)
 
 void intel_modeset_gem_init(struct drm_device *dev)
 {
-	intel_modeset_init_hw(dev);
+	intel_modeset_init_hw(dev, false);
 
 	intel_setup_overlay(dev);
 }
-- 
1.7.7.6