[PATCH 4/4] drm/i915: get/put PC8 when we get/put a CRTC

[Paulo Zanoni <przanoni@gmail.com>]

From: Paulo Zanoni <paulo.r.zanoni@intel.com>

Currently, PC8 is enabled at modeset_global_resources, which is called
after intel_modeset_update_state. Due to this, there's a small race
condition on the case where we start enabling PC8, then do a modeset
while PC8 is still being enabled. The racing condition triggers a WARN
because intel_modeset_update_state will mark the CRTC as enabled, then
the thread that's still enabling PC8 might look at the data structure
and think that PC8 is being enabled while a pipe is enabled. Despite
the WARN, this is not really a bug since we'll wait for the
PC8-enabling thread to finish when we call modeset_global_resources.

So this patch makes sure we get/put PC8 before we update
drm_crtc->enabled, because this will grab the PC8 lock, which will
wait for the PC8-enable task to finish.

The side-effect benefit of this patch is that we have a nice place to
track enabled/disabled CRTCs, so we may want to move some code from
modeset_global_resources to intel_crtc_set_state in the future.

The problem fixed by this patch can be reproduced by the
modeset-lpsp-stress-no-wait subtest from the pc8 test of
intel-gpu-tools.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
---
 drivers/gpu/drm/i915/intel_display.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index c226f4d..e841cd7 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -6409,6 +6409,7 @@ void hsw_enable_pc8_work(struct work_struct *__work)
 
 	DRM_DEBUG_KMS("Enabling package C8+\n");
 
+	mutex_lock(&dev_priv->pc8.lock);
 	dev_priv->pc8.enabled = true;
 
 	if (dev_priv->pch_id == INTEL_PCH_LPT_LP_DEVICE_ID_TYPE) {
@@ -6420,6 +6421,7 @@ void hsw_enable_pc8_work(struct work_struct *__work)
 	lpt_disable_clkout_dp(dev);
 	hsw_pc8_disable_interrupts(dev);
 	hsw_disable_lcpll(dev_priv, true, true);
+	mutex_unlock(&dev_priv->pc8.lock);
 }
 
 static void __hsw_enable_package_c8(struct drm_i915_private *dev_priv)
@@ -8880,6 +8882,24 @@ static bool intel_crtc_in_use(struct drm_crtc *crtc)
 	return false;
 }
 
+/* Sets crtc->base.enabled and gets/puts whatever resources are needed by the
+ * CRTC. */
+static void intel_crtc_set_state(struct intel_crtc *crtc, bool enabled)
+{
+	struct drm_device *dev = crtc->base.dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+
+	if (enabled == crtc->base.enabled)
+		return;
+
+	if (enabled)
+		hsw_disable_package_c8(dev_priv);
+	else
+		hsw_enable_package_c8(dev_priv);
+
+	crtc->base.enabled = enabled;
+}
+
 static void
 intel_modeset_update_state(struct drm_device *dev, unsigned prepare_pipes)
 {
@@ -8903,7 +8923,8 @@ intel_modeset_update_state(struct drm_device *dev, unsigned prepare_pipes)
 	/* Update computed state. */
 	list_for_each_entry(intel_crtc, &dev->mode_config.crtc_list,
 			    base.head) {
-		intel_crtc->base.enabled = intel_crtc_in_use(&intel_crtc->base);
+		intel_crtc_set_state(intel_crtc,
+				     intel_crtc_in_use(&intel_crtc->base));
 	}
 
 	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
@@ -10695,7 +10716,7 @@ static void intel_sanitize_crtc(struct intel_crtc *crtc)
 		}
 
 		WARN_ON(crtc->active);
-		crtc->base.enabled = false;
+		intel_crtc_set_state(crtc, false);
 	}
 
 	if (dev_priv->quirks & QUIRK_PIPEA_FORCE &&
@@ -10722,7 +10743,7 @@ static void intel_sanitize_crtc(struct intel_crtc *crtc)
 			      crtc->base.enabled ? "enabled" : "disabled",
 			      crtc->active ? "enabled" : "disabled");
 
-		crtc->base.enabled = crtc->active;
+		intel_crtc_set_state(crtc, crtc->active);
 
 		/* Because we only establish the connector -> encoder ->
 		 * crtc links if something is active, this means the
@@ -10819,7 +10840,7 @@ static void intel_modeset_readout_hw_state(struct drm_device *dev)
 		crtc->active = dev_priv->display.get_pipe_config(crtc,
 								 &crtc->config);
 
-		crtc->base.enabled = crtc->active;
+		intel_crtc_set_state(crtc, crtc->active);
 		crtc->primary_enabled = crtc->active;
 
 		DRM_DEBUG_KMS("[CRTC:%d] hw state readout: %s\n",
-- 
1.8.3.1