[PATCH] drm/i915: Skip modeset locking when atomic pageflips are used.

[Maarten Lankhorst]

With the atomic helper for pageflips there are no CS flips when
that require resetting, so on most platforms we can completely
skip the locking.

Because we may end up reverting the page_flip patch add an explicit
function pointer check so that if someone reverts the page flip patch
there will not be any issues if this is forgotten.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Testcase: kms_busy.extended-modeset-hang-oldfb-*
---
This is a standalone patch to fix modeset hangs on g4x+.

The path for gen4 and lower is simulated in kms_busy.extended-modeset-hang-oldfb-with-reset
and still fails.

 drivers/gpu/drm/i915/intel_display.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index d8db1caec1b8..1dd480a6752a 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3529,6 +3529,8 @@ static bool gpu_reset_clobbers_display(struct drm_i915_private *dev_priv)
 		INTEL_GEN(dev_priv) < 5 && !IS_G4X(dev_priv);
 }
 
+static const struct drm_crtc_funcs intel_crtc_funcs;
+
 void intel_prepare_reset(struct drm_i915_private *dev_priv)
 {
 	struct drm_device *dev = &dev_priv->drm;
@@ -3536,6 +3538,11 @@ void intel_prepare_reset(struct drm_i915_private *dev_priv)
 	struct drm_atomic_state *state;
 	int ret;
 
+	if (intel_crtc_funcs.page_flip == drm_atomic_helper_page_flip &&
+	    !i915.force_reset_modeset_test &&
+	    !gpu_reset_clobbers_display(dev_priv))
+		return;
+
 	/*
 	 * Need mode_config.mutex so that we don't
 	 * trample ongoing ->detect() and whatnot.
@@ -3584,6 +3591,11 @@ void intel_finish_reset(struct drm_i915_private *dev_priv)
 	struct drm_atomic_state *state = dev_priv->modeset_restore_state;
 	int ret;
 
+	if (intel_crtc_funcs.page_flip == drm_atomic_helper_page_flip &&
+	    !i915.force_reset_modeset_test &&
+	    !gpu_reset_clobbers_display(dev_priv))
+		return;
+
 	/*
 	 * Flips in the rings will be nuked by the reset,
 	 * so complete all pending flips so that user space
-- 
2.7.4