[Intel-gfx] [PATCH 1/2] Revert "drm/i915: Avoid waking the engines just to check if they are idle"

[Chris Wilson]

This reverts commit 0b702dca26580e3bbfbbaf22dfc29280b6263414.

CI reports that this is not as reliable as it first appears, with
failures starting to sporadically occur in selftests.

Fixes: 0b702dca2658 ("drm/i915: Avoid waking the engines just to check if they are idle")
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at intel.com>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_engine_cs.c | 17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index 4f244019560d..b7b626195eda 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -968,7 +968,6 @@ static bool ring_is_idle(struct intel_engine_cs *engine)
 {
 	struct drm_i915_private *dev_priv = engine->i915;
 	intel_wakeref_t wakeref;
-	unsigned long flags;
 	bool idle = true;
 
 	if (I915_SELFTEST_ONLY(!engine->mmio_base))
@@ -979,19 +978,15 @@ static bool ring_is_idle(struct intel_engine_cs *engine)
 	if (!wakeref)
 		return true;
 
-	spin_lock_irqsave(&dev_priv->uncore.lock, flags);
+	/* First check that no commands are left in the ring */
+	if ((I915_READ_HEAD(engine) & HEAD_ADDR) !=
+	    (I915_READ_TAIL(engine) & TAIL_ADDR))
+		idle = false;
 
-	/*
-	 * Check that no commands are left in the ring.
-	 *
-	 * If the engine is not awake, both reads return 0 as we do so without
-	 * forcewake.
-	 */
-	if ((I915_READ_FW(RING_HEAD(engine->mmio_base)) & HEAD_ADDR) !=
-	    (I915_READ_FW(RING_TAIL(engine->mmio_base)) & TAIL_ADDR))
+	/* No bit for gen2, so assume the CS parser is idle */
+	if (INTEL_GEN(dev_priv) > 2 && !(I915_READ_MODE(engine) & MODE_IDLE))
 		idle = false;
 
-	spin_unlock_irqrestore(&dev_priv->uncore.lock, flags);
 	intel_runtime_pm_put(dev_priv, wakeref);
 
 	return idle;
-- 
2.20.1