[PATCH 2/5] drm/i915: Report both waiters and success from intel_engine_wakeup()

[Chris Wilson]

The two users of the return value from intel_engine_wakeup() are
expecting different results. In the breadcrumbs hangcheck, we are using
it to determine whether wake_up_process() detected the waiter was
currently running (and if so we presume that it hasn't yet missed the
interrupt). However, in the fake_irq path, we are using the return value
as a check as to whether there are any waiters, and so we may
incorrectly stop the fake-irq if that waiter was currently running.

To handle the two different needs, return both bits of information!

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_breadcrumbs.c | 28 +++++++++++++++++++++++++++-
 drivers/gpu/drm/i915/intel_ringbuffer.h  | 26 +++-----------------------
 2 files changed, 30 insertions(+), 24 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index 027c93e34c97..a36f6bfccdb1 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -26,6 +26,32 @@
 
 #include "i915_drv.h"
 
+unsigned int intel_engine_wakeup(const struct intel_engine_cs *engine)
+{
+	unsigned int ret = 0;
+
+	/* Note that for this not to dangerously chase a dangling pointer,
+	 * we must hold the rcu_read_lock here.
+	 *
+	 * Also note that tsk is likely to be in !TASK_RUNNING state so an
+	 * early test for tsk->state != TASK_RUNNING before wake_up_process()
+	 * is unlikely to be beneficial.
+	 */
+	if (intel_engine_has_waiter(engine)) {
+		struct task_struct *tsk;
+
+		ret = ENGINE_WAKEUP_WAITER;
+
+		rcu_read_lock();
+		tsk = rcu_dereference(engine->breadcrumbs.irq_seqno_bh);
+		if (tsk && !wake_up_process(tsk))
+			ret |= ENGINE_WAKEUP_ACTIVE;
+		rcu_read_unlock();
+	}
+
+	return ret;
+}
+
 static unsigned long wait_timeout(void)
 {
 	return round_jiffies_up(jiffies + DRM_I915_HANGCHECK_JIFFIES);
@@ -49,7 +75,7 @@ static void intel_breadcrumbs_hangcheck(unsigned long data)
 	 * to process the pending interrupt (e.g, low priority task on a loaded
 	 * system) and wait until it sleeps before declaring a missed interrupt.
 	 */
-	if (!intel_engine_wakeup(engine)) {
+	if (intel_engine_wakeup(engine) & ENGINE_WAKEUP_ACTIVE) {
 		mod_timer(&b->hangcheck, wait_timeout());
 		return;
 	}
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 0f29e07a9581..78669d9708e4 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -642,29 +642,9 @@ static inline bool intel_engine_has_waiter(const struct intel_engine_cs *engine)
 	return rcu_access_pointer(engine->breadcrumbs.irq_seqno_bh);
 }
 
-static inline bool intel_engine_wakeup(const struct intel_engine_cs *engine)
-{
-	bool wakeup = false;
-
-	/* Note that for this not to dangerously chase a dangling pointer,
-	 * we must hold the rcu_read_lock here.
-	 *
-	 * Also note that tsk is likely to be in !TASK_RUNNING state so an
-	 * early test for tsk->state != TASK_RUNNING before wake_up_process()
-	 * is unlikely to be beneficial.
-	 */
-	if (intel_engine_has_waiter(engine)) {
-		struct task_struct *tsk;
-
-		rcu_read_lock();
-		tsk = rcu_dereference(engine->breadcrumbs.irq_seqno_bh);
-		if (tsk)
-			wakeup = wake_up_process(tsk);
-		rcu_read_unlock();
-	}
-
-	return wakeup;
-}
+unsigned int intel_engine_wakeup(const struct intel_engine_cs *engine);
+#define ENGINE_WAKEUP_WAITER BIT(0)
+#define ENGINE_WAKEUP_ACTIVE BIT(1)
 
 void intel_engine_reset_breadcrumbs(struct intel_engine_cs *engine);
 void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine);
-- 
2.11.0