drm/i915: add support for checking RPM atomic sections

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)
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1450203038-5150-10-git-send-email-imre.deak@intel.com

4 files changed, 21 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 74f1d78cbe2e..1943b8f0e684 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1606,6 +1606,7 @@ 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 eff7d2e7d71b..d523ebb2f89d 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 3232305301ca..8d0d6f59a72b 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -7247,4 +7247,5 @@ 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 4c80d2adac70..a0b9eaf77fe9 100644
--- a/drivers/gpu/drm/i915/intel_runtime_pm.c
+++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
@@ -2287,7 +2287,8 @@ 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);