[PATCH 15/71] drm/i915: Stop parking the signaler around reset

[Chris Wilson <chris@chris-wilson.co.uk>]

We cannot call kthread_park() from softirq context, so let's avoid it
entirely during the reset. We wanted to suspend the signaler so that it
would not mark a request as complete at the same time as we marked it as
being in error. Instead of parking the signaling, stop the engine from
advancing so that the GPU doesn't emit the breadcrumb for our chosen
"guilty" request.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Michał Winiarski <michal.winiarski@intel.com>
CC: Michel Thierry <michel.thierry@intel.com>
Cc: Jeff McGee <jeff.mcgee@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
---
 drivers/gpu/drm/i915/i915_gem.c         | 14 --------------
 drivers/gpu/drm/i915/intel_lrc.c        | 21 +++++++++++++++++++++
 drivers/gpu/drm/i915/intel_ringbuffer.c | 18 ++++++++++++++++++
 3 files changed, 39 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 694471fba777..022a84ac0c74 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3013,18 +3013,6 @@ i915_gem_reset_prepare_engine(struct intel_engine_cs *engine)
 	 */
 	intel_uncore_forcewake_get(engine->i915, FORCEWAKE_ALL);
 
-	/*
-	 * Prevent the signaler thread from updating the request
-	 * state (by calling dma_fence_signal) as we are processing
-	 * the reset. The write from the GPU of the seqno is
-	 * asynchronous and the signaler thread may see a different
-	 * value to us and declare the request complete, even though
-	 * the reset routine have picked that request as the active
-	 * (incomplete) request. This conflict is not handled
-	 * gracefully!
-	 */
-	kthread_park(engine->breadcrumbs.signaler);
-
 	request = engine->reset.prepare(engine);
 	if (request && request->fence.error == -EIO)
 		request = ERR_PTR(-EIO); /* Previous reset failed! */
@@ -3227,8 +3215,6 @@ void i915_gem_reset_finish_engine(struct intel_engine_cs *engine)
 {
 	engine->reset.finish(engine);
 
-	kthread_unpark(engine->breadcrumbs.signaler);
-
 	intel_uncore_forcewake_put(engine->i915, FORCEWAKE_ALL);
 }
 
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index a60c3afd0adb..bcebcd6f2848 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1852,6 +1852,21 @@ static void tasklet_kill_and_disable(struct tasklet_struct *t)
 	smp_mb();
 }
 
+static void set_stop_engine(struct intel_engine_cs *engine)
+{
+	struct drm_i915_private *dev_priv = engine->i915;
+	const u32 base = engine->mmio_base;
+	const i915_reg_t mode = RING_MI_MODE(base);
+
+	GEM_TRACE("%s\n", engine->name);
+	I915_WRITE_FW(mode, _MASKED_BIT_ENABLE(STOP_RING));
+	if (__intel_wait_for_register_fw(dev_priv,
+					 mode, MODE_IDLE, MODE_IDLE,
+					 1000, 0,
+					 NULL))
+		GEM_TRACE("%s: timed out on STOP_RING -> IDLE\n", engine->name);
+}
+
 static struct i915_request *
 execlists_reset_prepare(struct intel_engine_cs *engine)
 {
@@ -1898,6 +1913,12 @@ execlists_reset_prepare(struct intel_engine_cs *engine)
 	if (request) {
 		unsigned long flags;
 
+		/*
+		 * Prevent the breadcrumb from advancing before we decide
+		 * which request is currently active.
+		 */
+		set_stop_engine(engine);
+
 		spin_lock_irqsave(&engine->timeline.lock, flags);
 		list_for_each_entry_from_reverse(request,
 						 &engine->timeline.requests,
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 1e37e1be16c2..166901cbfa88 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -531,8 +531,26 @@ static int init_ring_common(struct intel_engine_cs *engine)
 	return ret;
 }
 
+static void set_stop_engine(struct intel_engine_cs *engine)
+{
+	struct drm_i915_private *dev_priv = engine->i915;
+	const u32 base = engine->mmio_base;
+	const i915_reg_t mode = RING_MI_MODE(base);
+
+	I915_WRITE_FW(mode, _MASKED_BIT_ENABLE(STOP_RING));
+	if (__intel_wait_for_register_fw(dev_priv,
+					 mode, MODE_IDLE, MODE_IDLE,
+					 1000, 0,
+					 NULL))
+		DRM_DEBUG_DRIVER("%s: timed out on STOP_RING\n",
+				 engine->name);
+}
+
 static struct i915_request *reset_prepare(struct intel_engine_cs *engine)
 {
+	if (INTEL_GEN(engine->i915) >= 3)
+		set_stop_engine(engine);
+
 	if (engine->irq_seqno_barrier)
 		engine->irq_seqno_barrier(engine);
 
-- 
2.17.0

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