[PATCH 09/10] drm/i915: add support for checking RPM atomic sections

[Imre Deak <imre.deak@intel.com>]

In some cases we want to check whether we hold an RPM wakelock reference
for the whole duration of a sequence. To achieve this add a new RPM atomic sequence
counter that we increment any time the wakelock refcount drops to zero.
Check whether the sequence number stays the same during the atomic
section and that we hold the wakelock at the beginning of the section.

Motivated by Chris.

v2-v3:
- unchanged
v4:
- swap the order of atomic_read() and assert_rpm_wakelock_held() in
  assert_rpm_atomic_begin() to avoid race

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> (v3)
---
 drivers/gpu/drm/i915/i915_drv.h         |  1 +
 drivers/gpu/drm/i915/intel_drv.h        | 17 +++++++++++++++++
 drivers/gpu/drm/i915/intel_pm.c         |  1 +
 drivers/gpu/drm/i915/intel_runtime_pm.c |  3 ++-
 4 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 2894716..00ce627 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1603,6 +1603,7 @@ struct skl_wm_level {
  */
 struct i915_runtime_pm {
 	atomic_t wakeref_count;
+	atomic_t atomic_seq;
 	bool suspended;
 	bool irqs_enabled;
 };
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index d8e4aca..88d37eb 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -1446,6 +1446,23 @@ assert_rpm_wakelock_held(struct drm_i915_private *dev_priv)
 		  "RPM wakelock ref not held during HW access");
 }
 
+static inline int
+assert_rpm_atomic_begin(struct drm_i915_private *dev_priv)
+{
+	int seq = atomic_read(&dev_priv->pm.atomic_seq);
+
+	assert_rpm_wakelock_held(dev_priv);
+
+	return seq;
+}
+
+static inline void
+assert_rpm_atomic_end(struct drm_i915_private *dev_priv, int begin_seq)
+{
+	WARN_ONCE(atomic_read(&dev_priv->pm.atomic_seq) != begin_seq,
+		 "HW access outside of RPM atomic section\n");
+}
+
 /**
  * disable_rpm_wakeref_asserts - disable the RPM assert checks
  * @dev_priv: i915 device instance
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 6c08537..6eb9606 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -7248,4 +7248,5 @@ void intel_pm_setup(struct drm_device *dev)
 
 	dev_priv->pm.suspended = false;
 	atomic_set(&dev_priv->pm.wakeref_count, 0);
+	atomic_set(&dev_priv->pm.atomic_seq, 0);
 }
diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.c b/drivers/gpu/drm/i915/intel_runtime_pm.c
index 82c55a9..cee54ea 100644
--- a/drivers/gpu/drm/i915/intel_runtime_pm.c
+++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
@@ -2283,7 +2283,8 @@ void intel_runtime_pm_put(struct drm_i915_private *dev_priv)
 	struct device *device = &dev->pdev->dev;
 
 	assert_rpm_wakelock_held(dev_priv);
-	atomic_dec(&dev_priv->pm.wakeref_count);
+	if (atomic_dec_and_test(&dev_priv->pm.wakeref_count))
+		atomic_inc(&dev_priv->pm.atomic_seq);
 
 	pm_runtime_mark_last_busy(device);
 	pm_runtime_put_autosuspend(device);
-- 
2.5.0

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