[Intel-gfx] [PATCH 01/12] drm/i915: add helper to get a display power ref if it was already enabled

[Imre Deak]

We have many places in the code where we check if a given display power
domain is enabled and if so access registers backed by this power
domain. We assumed that some modeset lock will prevent the power
reference from vanishing in the middle of the HW access, but this
assumption doesn't always hold. In such cases we get either the wakeref
not held, or an unclaimed register access error message. To fix this in
a future-proof way that's independent of other locks wrap any such
access with a get_ref_if_enabled()/put_ref() pair.

Kudos to Ville and Joonas for the ideas of this new interface.

CC: Mika Kuoppala <mika.kuoppala at intel.com>
CC: Chris Wilson <chris at chris-wilson.co.uk>
CC: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
CC: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/i915/intel_drv.h        |   3 +
 drivers/gpu/drm/i915/intel_runtime_pm.c | 111 ++++++++++++++++++++++++++------
 2 files changed, 96 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 878172a..9380ffe 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -1436,6 +1436,8 @@ bool __intel_display_power_is_enabled(struct drm_i915_private *dev_priv,
 				      enum intel_display_power_domain domain);
 void intel_display_power_get(struct drm_i915_private *dev_priv,
 			     enum intel_display_power_domain domain);
+bool intel_display_power_get_if_enabled(struct drm_i915_private *dev_priv,
+					enum intel_display_power_domain domain);
 void intel_display_power_put(struct drm_i915_private *dev_priv,
 			     enum intel_display_power_domain domain);
 
@@ -1522,6 +1524,7 @@ enable_rpm_wakeref_asserts(struct drm_i915_private *dev_priv)
 	enable_rpm_wakeref_asserts(dev_priv)
 
 void intel_runtime_pm_get(struct drm_i915_private *dev_priv);
+bool intel_runtime_pm_get_if_in_use(struct drm_i915_private *dev_priv);
 void intel_runtime_pm_get_noresume(struct drm_i915_private *dev_priv);
 void intel_runtime_pm_put(struct drm_i915_private *dev_priv);
 
diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.c b/drivers/gpu/drm/i915/intel_runtime_pm.c
index bbca527..a81f965 100644
--- a/drivers/gpu/drm/i915/intel_runtime_pm.c
+++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
@@ -1435,39 +1435,90 @@ static void chv_pipe_power_well_disable(struct drm_i915_private *dev_priv,
 	chv_set_pipe_power_well(dev_priv, power_well, false);
 }
 
-/**
- * intel_display_power_get - grab a power domain reference
- * @dev_priv: i915 device instance
- * @domain: power domain to reference
- *
- * This function grabs a power domain reference for @domain and ensures that the
- * power domain and all its parents are powered up. Therefore users should only
- * grab a reference to the innermost power domain they need.
- *
- * Any power domain reference obtained by this function must have a symmetric
- * call to intel_display_power_put() to release the reference again.
- */
-void intel_display_power_get(struct drm_i915_private *dev_priv,
-			     enum intel_display_power_domain domain)
+static void
+__intel_display_power_get_domain(struct drm_i915_private *dev_priv,
+				 enum intel_display_power_domain domain)
 {
 	struct i915_power_domains *power_domains;
 	struct i915_power_well *power_well;
 	int i;
 
-	intel_runtime_pm_get(dev_priv);
-
 	power_domains = &dev_priv->power_domains;
 
-	mutex_lock(&power_domains->lock);
-
 	for_each_power_well(i, power_well, BIT(domain), power_domains) {
 		if (!power_well->count++)
 			intel_power_well_enable(dev_priv, power_well);
 	}
 
 	power_domains->domain_use_count[domain]++;
+}
+
+/**
+ * intel_display_power_get - grab a power domain reference
+ * @dev_priv: i915 device instance
+ * @domain: power domain to reference
+ *
+ * This function grabs a power domain reference for @domain and ensures that the
+ * power domain and all its parents are powered up. Therefore users should only
+ * grab a reference to the innermost power domain they need.
+ *
+ * Any power domain reference obtained by this function must have a symmetric
+ * call to intel_display_power_put() to release the reference again.
+ */
+void intel_display_power_get(struct drm_i915_private *dev_priv,
+			     enum intel_display_power_domain domain)
+{
+	struct i915_power_domains *power_domains;
+
+	intel_runtime_pm_get(dev_priv);
+
+	power_domains = &dev_priv->power_domains;
+
+	mutex_lock(&power_domains->lock);
+
+	__intel_display_power_get_domain(dev_priv, domain);
+
+	mutex_unlock(&power_domains->lock);
+}
+
+/**
+ * intel_display_power_get_if_enabled - grab a reference for an enabled display power domain
+ * @dev_priv: i915 device instance
+ * @domain: power domain to reference
+ *
+ * This function grabs a power domain reference for @domain and ensures that the
+ * power domain and all its parents are powered up. Therefore users should only
+ * grab a reference to the innermost power domain they need.
+ *
+ * Any power domain reference obtained by this function must have a symmetric
+ * call to intel_display_power_put() to release the reference again.
+ */
+bool intel_display_power_get_if_enabled(struct drm_i915_private *dev_priv,
+					enum intel_display_power_domain domain)
+{
+	struct i915_power_domains *power_domains;
+	bool is_enabled;
+
+	if (!intel_runtime_pm_get_if_in_use(dev_priv))
+		return false;
+
+	power_domains = &dev_priv->power_domains;
+
+	mutex_lock(&power_domains->lock);
+
+	if (__intel_display_power_is_enabled(dev_priv, domain)) {
+		__intel_display_power_get_domain(dev_priv, domain);
+		is_enabled = true;
+	} else {
+		is_enabled = false;
+	}
 
 	mutex_unlock(&power_domains->lock);
+
+	if (!is_enabled)
+		intel_runtime_pm_put(dev_priv);
+
+	return is_enabled;
 }
 
 /**
@@ -2239,6 +2290,30 @@ void intel_runtime_pm_get(struct drm_i915_private *dev_priv)
 }
 
 /**
+ * intel_runtime_pm_get_if_in_use - grab a runtime pm reference if device in use
+ * @dev_priv: i915 device instance
+ *
+ * This function grabs a device-level runtime pm reference if the device is
+ * already in use and ensures that it is powered up.
+ *
+ * Any runtime pm reference obtained by this function must have a symmetric
+ * call to intel_runtime_pm_put() to release the reference again.
+ */
+bool intel_runtime_pm_get_if_in_use(struct drm_i915_private *dev_priv)
+{
+	struct drm_device *dev = dev_priv->dev;
+	struct device *device = &dev->pdev->dev;
+
+	if (IS_ENABLED(CONFIG_PM) && !pm_runtime_get_if_in_use(device))
+		return false;
+
+	atomic_inc(&dev_priv->pm.wakeref_count);
+	assert_rpm_wakelock_held(dev_priv);
+
+	return true;
+}
+
+/**
  * intel_runtime_pm_get_noresume - grab a runtime pm reference
  * @dev_priv: i915 device instance
  *
-- 
2.5.0