[PATCH 04/25] drm/i915: Check caller held wakerefs in assert_forcewakes_active

[Chris Wilson]

The intent of the assert is to document that the caller took the
appropriate wakerefs for the function. However, as Tvrtko pointed out,
we simply check whether the fw_domains are active and may be confused by
the auto wakeref which may be dropped between the check and use. Let's
be more careful in the assert and check that each fw_domain has an
explicit caller wakeref above and beyond the automatic wakeref.

Reported-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_uncore.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index 68d54e126d79..bc25a6e51463 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -738,6 +738,12 @@ void assert_forcewakes_inactive(struct intel_uncore *uncore)
 void assert_forcewakes_active(struct intel_uncore *uncore,
 			      enum forcewake_domains fw_domains)
 {
+	struct intel_uncore_forcewake_domain *domain;
+	unsigned int tmp;
+
+	if (!IS_ENABLED(CONFIG_DRM_i915_RUNTIME_PM))
+		return;
+
 	if (!uncore->funcs.force_wake_get)
 		return;
 
@@ -747,6 +753,24 @@ void assert_forcewakes_active(struct intel_uncore *uncore,
 	WARN(fw_domains & ~uncore->fw_domains_active,
 	     "Expected %08x fw_domains to be active, but %08x are off\n",
 	     fw_domains, fw_domains & ~uncore->fw_domains_active);
+
+	/*
+	 * Check that the caller has an explicit wakeref and we don't mistake
+	 * it for the auto wakeref.
+	 */
+	local_irq_disable();
+	for_each_fw_domain_masked(domain, fw_domains, uncore, tmp) {
+		unsigned int expect = 1;
+
+		if (hrtimer_active(&domain->timer))
+			expect++;
+
+		if (WARN(domain->wake_count < expect,
+			 "Expected domain %d to be held awake by caller\n",
+			 domain->id))
+			break;
+	}
+	local_irq_enable();
 }
 
 /* We give fast paths for the really cool registers */
-- 
2.20.1