drm/i915: add support for checking if we hold an RPM reference

Atm, we assert that the device is not suspended until the point when the
device is truly put to a suspended state. This is fine, but we can catch
more problems if we check that RPM refcount is non-zero. After that one
drops to zero we shouldn't access the device any more, even if the actual
device suspend may be delayed. Change assert_rpm_wakelock_held()
accordingly to check for a non-zero RPM refcount in addition to the
current device-not-suspended check.

For the new asserts to work we need to annotate every place explicitly in
the code where we expect that the device is powered. The places where we
only assume this, but may not hold an RPM reference:
- driver load
  We assume the device to be powered until we enable RPM. Make this
  explicit by taking an RPM reference around the load function.
- system and runtime sudpend/resume handlers
  These handlers are called when the RPM reference becomes 0 and know the
  exact point after which the device can get powered off. Disable the
  RPM-reference-held check for their duration.
- the IRQ, hangcheck and RPS work handlers
  These handlers are flushed in the system/runtime suspend handler
  before the device is powered off, so it's guaranteed that they won't
  run while the device is powered off even though they don't hold any
  RPM reference. Disable the RPM-reference-held check for their duration.

In all these cases we still check that the device is not suspended.
These explicit annotations also have the positive side effect of
documenting our assumptions better.

This caught additional WARNs from the atomic modeset path, those should
be fixed separately.

v2:
- remove the redundant HAS_RUNTIME_PM check (moved to patch 1) (Ville)
v3:
- use a new dedicated RPM wakelock refcount to also catch cases where
  our own RPM get/put functions were not called (Chris)
- assert also that the new RPM wakelock refcount is 0 in the RPM
  suspend handler (Chris)
- change the assert error message to be more meaningful (Chris)
- prevent false assert errors and check that the RPM wakelock is 0 in
  the RPM resume handler too
- prevent false assert errors in the hangcheck work too
- add a device not suspended assert check to the hangcheck work
v4:
- rename disable/enable_rpm_asserts to disable/enable_rpm_wakeref_asserts
  and wakelock_count to wakeref_count
- disable the wakeref asserts in the IRQ handlers and RPS work too
- update/clarify commit message
v5:
- mark places we plan to change to use proper RPM refcounting with
  separate DISABLE/ENABLE_RPM_WAKEREF_ASSERTS aliases (Chris)
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1450227139-13471-1-git-send-email-imre.deak@intel.com

drivers/gpu/drm/i915/i915_dma.c

@@ -896,6 +896,8 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 
 	intel_pm_setup(dev);
 
+	intel_runtime_pm_get(dev_priv);
+
 	intel_display_crc_init(dev);
 
 	i915_dump_device_info(dev_priv);
@@ -1085,6 +1087,8 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 
 	i915_audio_component_init(dev_priv);
 
+	intel_runtime_pm_put(dev_priv);
+
 	return 0;
 
 out_power_well:
@@ -1120,6 +1124,9 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 	kmem_cache_destroy(dev_priv->requests);
 	kmem_cache_destroy(dev_priv->vmas);
 	kmem_cache_destroy(dev_priv->objects);
+
+	intel_runtime_pm_put(dev_priv);
+
 	kfree(dev_priv);
 	return ret;
 }

drivers/gpu/drm/i915/i915_drv.c

@@ -577,6 +577,8 @@ static int i915_drm_suspend(struct drm_device *dev)
 	dev_priv->modeset_restore = MODESET_SUSPENDED;
 	mutex_unlock(&dev_priv->modeset_restore_lock);
 
+	disable_rpm_wakeref_asserts(dev_priv);
+
 	/* We do a lot of poking in a lot of registers, make sure they work
 	 * properly. */
 	intel_display_set_init_power(dev_priv, true);
@@ -589,7 +591,7 @@ static int i915_drm_suspend(struct drm_device *dev)
 	if (error) {
 		dev_err(&dev->pdev->dev,
 			"GEM idle failed, resume might fail\n");
-		return error;
+		goto out;
 	}
 
 	intel_guc_suspend(dev);
@@ -632,7 +634,10 @@ static int i915_drm_suspend(struct drm_device *dev)
 	if (HAS_CSR(dev_priv))
 		flush_work(&dev_priv->csr.work);
 
-	return 0;
+out:
+	enable_rpm_wakeref_asserts(dev_priv);
+
+	return error;
 }
 
 static int i915_drm_suspend_late(struct drm_device *drm_dev, bool hibernation)
@@ -641,6 +646,8 @@ static int i915_drm_suspend_late(struct drm_device *drm_dev, bool hibernation)
 	bool fw_csr;
 	int ret;
 
+	disable_rpm_wakeref_asserts(dev_priv);
+
 	fw_csr = suspend_to_idle(dev_priv) && dev_priv->csr.dmc_payload;
 	/*
 	 * In case of firmware assisted context save/restore don't manually
@@ -659,7 +666,7 @@ static int i915_drm_suspend_late(struct drm_device *drm_dev, bool hibernation)
 		if (!fw_csr)
 			intel_power_domains_init_hw(dev_priv, true);
 
-		return ret;
+		goto out;
 	}
 
 	pci_disable_device(drm_dev->pdev);
@@ -680,7 +687,10 @@ static int i915_drm_suspend_late(struct drm_device *drm_dev, bool hibernation)
 
 	dev_priv->suspended_to_idle = suspend_to_idle(dev_priv);
 
-	return 0;
+out:
+	enable_rpm_wakeref_asserts(dev_priv);
+
+	return ret;
 }
 
 int i915_suspend_switcheroo(struct drm_device *dev, pm_message_t state)
@@ -711,6 +721,8 @@ static int i915_drm_resume(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
+	disable_rpm_wakeref_asserts(dev_priv);
+
 	mutex_lock(&dev->struct_mutex);
 	i915_gem_restore_gtt_mappings(dev);
 	mutex_unlock(&dev->struct_mutex);
@@ -775,6 +787,8 @@ static int i915_drm_resume(struct drm_device *dev)
 
 	drm_kms_helper_poll_enable(dev);
 
+	enable_rpm_wakeref_asserts(dev_priv);
+
 	return 0;
 }
 
@@ -799,6 +813,8 @@ static int i915_drm_resume_early(struct drm_device *dev)
 
 	pci_set_master(dev->pdev);
 
+	disable_rpm_wakeref_asserts(dev_priv);
+
 	if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
 		ret = vlv_resume_prepare(dev_priv, false);
 	if (ret)
@@ -820,6 +836,8 @@ static int i915_drm_resume_early(struct drm_device *dev)
 out:
 	dev_priv->suspended_to_idle = false;
 
+	enable_rpm_wakeref_asserts(dev_priv);
+
 	return ret;
 }
 
@@ -1452,6 +1470,9 @@ static int intel_runtime_suspend(struct device *device)
 
 		return -EAGAIN;
 	}
+
+	disable_rpm_wakeref_asserts(dev_priv);
+
 	/*
 	 * We are safe here against re-faults, since the fault handler takes
 	 * an RPM reference.
@@ -1471,10 +1492,15 @@ static int intel_runtime_suspend(struct device *device)
 		DRM_ERROR("Runtime suspend failed, disabling it (%d)\n", ret);
 		intel_runtime_pm_enable_interrupts(dev_priv);
 
+		enable_rpm_wakeref_asserts(dev_priv);
+
 		return ret;
 	}
 
 	intel_uncore_forcewake_reset(dev, false);
+
+	enable_rpm_wakeref_asserts(dev_priv);
+	WARN_ON_ONCE(atomic_read(&dev_priv->pm.wakeref_count));
 	dev_priv->pm.suspended = true;
 
 	/*
@@ -1518,6 +1544,9 @@ static int intel_runtime_resume(struct device *device)
 
 	DRM_DEBUG_KMS("Resuming device\n");
 
+	WARN_ON_ONCE(atomic_read(&dev_priv->pm.wakeref_count));
+	disable_rpm_wakeref_asserts(dev_priv);
+
 	intel_opregion_notify_adapter(dev, PCI_D0);
 	dev_priv->pm.suspended = false;
 
@@ -1552,6 +1581,8 @@ static int intel_runtime_resume(struct device *device)
 
 	intel_enable_gt_powersave(dev);
 
+	enable_rpm_wakeref_asserts(dev_priv);
+
 	if (ret)
 		DRM_ERROR("Runtime resume failed, disabling it (%d)\n", ret);
 	else

drivers/gpu/drm/i915/i915_drv.h

@@ -1605,6 +1605,7 @@ struct skl_wm_level {
  * For more, read the Documentation/power/runtime_pm.txt.
  */
 struct i915_runtime_pm {
+	atomic_t wakeref_count;
 	bool suspended;
 	bool irqs_enabled;
 };

drivers/gpu/drm/i915/i915_irq.c

@@ -1103,6 +1103,14 @@ static void gen6_pm_rps_work(struct work_struct *work)
 		spin_unlock_irq(&dev_priv->irq_lock);
 		return;
 	}
+
+	/*
+	 * The RPS work is synced during runtime suspend, we don't require a
+	 * wakeref. TODO: instead of disabling the asserts make sure that we
+	 * always hold an RPM reference while the work is running.
+	 */
+	DISABLE_RPM_WAKEREF_ASSERTS(dev_priv);
+
 	pm_iir = dev_priv->rps.pm_iir;
 	dev_priv->rps.pm_iir = 0;
 	/* Make sure not to corrupt PMIMR state used by ringbuffer on GEN6 */
@@ -1115,7 +1123,7 @@ static void gen6_pm_rps_work(struct work_struct *work)
 	WARN_ON(pm_iir & ~dev_priv->pm_rps_events);
 
 	if ((pm_iir & dev_priv->pm_rps_events) == 0 && !client_boost)
-		return;
+		goto out;
 
 	mutex_lock(&dev_priv->rps.hw_lock);
 
@@ -1170,6 +1178,8 @@ static void gen6_pm_rps_work(struct work_struct *work)
 	intel_set_rps(dev_priv->dev, new_delay);
 
 	mutex_unlock(&dev_priv->rps.hw_lock);
+out:
+	ENABLE_RPM_WAKEREF_ASSERTS(dev_priv);
 }
 
 
@@ -1758,6 +1768,9 @@ static irqreturn_t valleyview_irq_handler(int irq, void *arg)
 	if (!intel_irqs_enabled(dev_priv))
 		return IRQ_NONE;
 
+	/* IRQs are synced during runtime_suspend, we don't require a wakeref */
+	disable_rpm_wakeref_asserts(dev_priv);
+
 	while (true) {
 		/* Find, clear, then process each source of interrupt */
 
@@ -1792,6 +1805,8 @@ static irqreturn_t valleyview_irq_handler(int irq, void *arg)
 	}
 
 out:
+	enable_rpm_wakeref_asserts(dev_priv);
+
 	return ret;
 }
 
@@ -1805,6 +1820,9 @@ static irqreturn_t cherryview_irq_handler(int irq, void *arg)
 	if (!intel_irqs_enabled(dev_priv))
 		return IRQ_NONE;
 
+	/* IRQs are synced during runtime_suspend, we don't require a wakeref */
+	disable_rpm_wakeref_asserts(dev_priv);
+
 	for (;;) {
 		master_ctl = I915_READ(GEN8_MASTER_IRQ) & ~GEN8_MASTER_IRQ_CONTROL;
 		iir = I915_READ(VLV_IIR);
@@ -1835,6 +1853,8 @@ static irqreturn_t cherryview_irq_handler(int irq, void *arg)
 		POSTING_READ(GEN8_MASTER_IRQ);
 	}
 
+	enable_rpm_wakeref_asserts(dev_priv);
+
 	return ret;
 }
 
@@ -2165,6 +2185,9 @@ static irqreturn_t ironlake_irq_handler(int irq, void *arg)
 	if (!intel_irqs_enabled(dev_priv))
 		return IRQ_NONE;
 
+	/* IRQs are synced during runtime_suspend, we don't require a wakeref */
+	disable_rpm_wakeref_asserts(dev_priv);
+
 	/* We get interrupts on unclaimed registers, so check for this before we
 	 * do any I915_{READ,WRITE}. */
 	intel_uncore_check_errors(dev);
@@ -2223,6 +2246,9 @@ static irqreturn_t ironlake_irq_handler(int irq, void *arg)
 		POSTING_READ(SDEIER);
 	}
 
+	/* IRQs are synced during runtime_suspend, we don't require a wakeref */
+	enable_rpm_wakeref_asserts(dev_priv);
+
 	return ret;
 }
 
@@ -2255,6 +2281,9 @@ static irqreturn_t gen8_irq_handler(int irq, void *arg)
 	if (!intel_irqs_enabled(dev_priv))
 		return IRQ_NONE;
 
+	/* IRQs are synced during runtime_suspend, we don't require a wakeref */
+	disable_rpm_wakeref_asserts(dev_priv);
+
 	if (INTEL_INFO(dev_priv)->gen >= 9)
 		aux_mask |=  GEN9_AUX_CHANNEL_B | GEN9_AUX_CHANNEL_C |
 			GEN9_AUX_CHANNEL_D;
@@ -2262,7 +2291,7 @@ static irqreturn_t gen8_irq_handler(int irq, void *arg)
 	master_ctl = I915_READ_FW(GEN8_MASTER_IRQ);
 	master_ctl &= ~GEN8_MASTER_IRQ_CONTROL;
 	if (!master_ctl)
-		return IRQ_NONE;
+		goto out;
 
 	I915_WRITE_FW(GEN8_MASTER_IRQ, 0);
 
@@ -2393,6 +2422,9 @@ static irqreturn_t gen8_irq_handler(int irq, void *arg)
 	I915_WRITE_FW(GEN8_MASTER_IRQ, GEN8_MASTER_IRQ_CONTROL);
 	POSTING_READ_FW(GEN8_MASTER_IRQ);
 
+out:
+	enable_rpm_wakeref_asserts(dev_priv);
+
 	return ret;
 }
 
@@ -2989,6 +3021,13 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 	if (!i915.enable_hangcheck)
 		return;
 
+	/*
+	 * The hangcheck work is synced during runtime suspend, we don't
+	 * require a wakeref. TODO: instead of disabling the asserts make
+	 * sure that we hold a reference when this work is running.
+	 */
+	DISABLE_RPM_WAKEREF_ASSERTS(dev_priv);
+
 	for_each_ring(ring, dev_priv, i) {
 		u64 acthd;
 		u32 seqno;
@@ -3080,13 +3119,18 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 		}
 	}
 
-	if (rings_hung)
-		return i915_handle_error(dev, true, "Ring hung");
+	if (rings_hung) {
+		i915_handle_error(dev, true, "Ring hung");
+		goto out;
+	}
 
 	if (busy_count)
 		/* Reset timer case chip hangs without another request
 		 * being added */
 		i915_queue_hangcheck(dev);
+
+out:
+	ENABLE_RPM_WAKEREF_ASSERTS(dev_priv);
 }
 
 void i915_queue_hangcheck(struct drm_device *dev)
@@ -3878,13 +3922,18 @@ static irqreturn_t i8xx_irq_handler(int irq, void *arg)
 	u16 flip_mask =
 		I915_DISPLAY_PLANE_A_FLIP_PENDING_INTERRUPT |
 		I915_DISPLAY_PLANE_B_FLIP_PENDING_INTERRUPT;
+	irqreturn_t ret;
 
 	if (!intel_irqs_enabled(dev_priv))
 		return IRQ_NONE;
 
+	/* IRQs are synced during runtime_suspend, we don't require a wakeref */
+	disable_rpm_wakeref_asserts(dev_priv);
+
+	ret = IRQ_NONE;
 	iir = I915_READ16(IIR);
 	if (iir == 0)
-		return IRQ_NONE;
+		goto out;
 
 	while (iir & ~flip_mask) {
 		/* Can't rely on pipestat interrupt bit in iir as it might
@@ -3933,8 +3982,12 @@ static irqreturn_t i8xx_irq_handler(int irq, void *arg)
 
 		iir = new_iir;
 	}
+	ret = IRQ_HANDLED;
+
+out:
+	enable_rpm_wakeref_asserts(dev_priv);
 
-	return IRQ_HANDLED;
+	return ret;
 }
 
 static void i8xx_irq_uninstall(struct drm_device * dev)
@@ -4063,6 +4116,9 @@ static irqreturn_t i915_irq_handler(int irq, void *arg)
 	if (!intel_irqs_enabled(dev_priv))
 		return IRQ_NONE;
 
+	/* IRQs are synced during runtime_suspend, we don't require a wakeref */
+	disable_rpm_wakeref_asserts(dev_priv);
+
 	iir = I915_READ(IIR);
 	do {
 		bool irq_received = (iir & ~flip_mask) != 0;
@@ -4145,6 +4201,8 @@ static irqreturn_t i915_irq_handler(int irq, void *arg)
 		iir = new_iir;
 	} while (iir & ~flip_mask);
 
+	enable_rpm_wakeref_asserts(dev_priv);
+
 	return ret;
 }
 
@@ -4284,6 +4342,9 @@ static irqreturn_t i965_irq_handler(int irq, void *arg)
 	if (!intel_irqs_enabled(dev_priv))
 		return IRQ_NONE;
 
+	/* IRQs are synced during runtime_suspend, we don't require a wakeref */
+	disable_rpm_wakeref_asserts(dev_priv);
+
 	iir = I915_READ(IIR);
 
 	for (;;) {
@@ -4369,6 +4430,8 @@ static irqreturn_t i965_irq_handler(int irq, void *arg)
 		iir = new_iir;
 	}
 
+	enable_rpm_wakeref_asserts(dev_priv);
+
 	return ret;
 }
 

drivers/gpu/drm/i915/intel_drv.h

@@ -1442,8 +1442,58 @@ static inline void
 assert_rpm_wakelock_held(struct drm_i915_private *dev_priv)
 {
 	assert_rpm_device_not_suspended(dev_priv);
+	WARN_ONCE(!atomic_read(&dev_priv->pm.wakeref_count),
+		  "RPM wakelock ref not held during HW access");
 }
 
+/**
+ * disable_rpm_wakeref_asserts - disable the RPM assert checks
+ * @dev_priv: i915 device instance
+ *
+ * This function disable asserts that check if we hold an RPM wakelock
+ * reference, while keeping the device-not-suspended checks still enabled.
+ * It's meant to be used only in special circumstances where our rule about
+ * the wakelock refcount wrt. the device power state doesn't hold. According
+ * to this rule at any point where we access the HW or want to keep the HW in
+ * an active state we must hold an RPM wakelock reference acquired via one of
+ * the intel_runtime_pm_get() helpers. Currently there are a few special spots
+ * where this rule doesn't hold: the IRQ and suspend/resume handlers, the
+ * forcewake release timer, and the GPU RPS and hangcheck works. All other
+ * users should avoid using this function.
+ *
+ * Any calls to this function must have a symmetric call to
+ * enable_rpm_wakeref_asserts().
+ */
+static inline void
+disable_rpm_wakeref_asserts(struct drm_i915_private *dev_priv)
+{
+	atomic_inc(&dev_priv->pm.wakeref_count);
+}
+
+/**
+ * enable_rpm_wakeref_asserts - re-enable the RPM assert checks
+ * @dev_priv: i915 device instance
+ *
+ * This function re-enables the RPM assert checks after disabling them with
+ * disable_rpm_wakeref_asserts. It's meant to be used only in special
+ * circumstances otherwise its use should be avoided.
+ *
+ * Any calls to this function must have a symmetric call to
+ * disable_rpm_wakeref_asserts().
+ */
+static inline void
+enable_rpm_wakeref_asserts(struct drm_i915_private *dev_priv)
+{
+	atomic_dec(&dev_priv->pm.wakeref_count);
+}
+
+/* TODO: convert users of these to rely instead on proper RPM refcounting */
+#define DISABLE_RPM_WAKEREF_ASSERTS(dev_priv)	\
+	disable_rpm_wakeref_asserts(dev_priv)
+
+#define ENABLE_RPM_WAKEREF_ASSERTS(dev_priv)	\
+	enable_rpm_wakeref_asserts(dev_priv)
+
 void intel_runtime_pm_get(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);

drivers/gpu/drm/i915/intel_pm.c

@@ -7246,4 +7246,5 @@ void intel_pm_setup(struct drm_device *dev)
 	INIT_LIST_HEAD(&dev_priv->rps.mmioflips.link);
 
 	dev_priv->pm.suspended = false;
+	atomic_set(&dev_priv->pm.wakeref_count, 0);
 }

drivers/gpu/drm/i915/intel_runtime_pm.c

@@ -2240,6 +2240,8 @@ void intel_runtime_pm_get(struct drm_i915_private *dev_priv)
 	struct device *device = &dev->pdev->dev;
 
 	pm_runtime_get_sync(device);
+
+	atomic_inc(&dev_priv->pm.wakeref_count);
 	assert_rpm_wakelock_held(dev_priv);
 }
 
@@ -2267,6 +2269,8 @@ void intel_runtime_pm_get_noresume(struct drm_i915_private *dev_priv)
 
 	assert_rpm_wakelock_held(dev_priv);
 	pm_runtime_get_noresume(device);
+
+	atomic_inc(&dev_priv->pm.wakeref_count);
 }
 
 /**
@@ -2282,6 +2286,8 @@ void intel_runtime_pm_put(struct drm_i915_private *dev_priv)
 	struct drm_device *dev = dev_priv->dev;
 	struct device *device = &dev->pdev->dev;
 
+	atomic_dec(&dev_priv->pm.wakeref_count);
+
 	pm_runtime_mark_last_busy(device);
 	pm_runtime_put_autosuspend(device);
 }