[RFC 4/8] drm/i915: Split execlists/guc reset prepartions

[jeff.mcgee@xxxxxxxxx]

From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>

In the next patch, we will make the execlists reset prepare callback
take into account preemption by flushing the context-switch handler.
This is not applicable to the GuC submission backend, so split the two
into their own backend callbacks.

Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Michał Winiarski <michal.winiarski@xxxxxxxxx>
CC: Michel Thierry <michel.thierry@xxxxxxxxx>
Cc: Jeff McGee <jeff.mcgee@xxxxxxxxx>
---
 drivers/gpu/drm/i915/intel_guc_submission.c | 39 +++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_lrc.c            | 11 +-------
 2 files changed, 40 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_guc_submission.c b/drivers/gpu/drm/i915/intel_guc_submission.c
index 207cda062626..779c8d3156e5 100644
--- a/drivers/gpu/drm/i915/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/intel_guc_submission.c
@@ -776,6 +776,44 @@ static void guc_submission_tasklet(unsigned long data)
 		guc_dequeue(engine);
 }
 
+static struct i915_request *
+guc_reset_prepare(struct intel_engine_cs *engine)
+{
+	struct intel_engine_execlists * const execlists = &engine->execlists;
+
+	/*
+	 * Prevent request submission to the hardware until we have
+	 * completed the reset in i915_gem_reset_finish(). If a request
+	 * is completed by one engine, it may then queue a request
+	 * to a second via its execlists->tasklet *just* as we are
+	 * calling engine->init_hw() and also writing the ELSP.
+	 * Turning off the execlists->tasklet until the reset is over
+	 * prevents the race.
+	 *
+	 * Note that this needs to be a single atomic operation on the
+	 * tasklet (flush existing tasks, prevent new tasks) to prevent
+	 * a race between reset and set-wedged. It is not, so we do the best
+	 * we can atm and make sure we don't lock the machine up in the more
+	 * common case of recursively being called from set-wedged from inside
+	 * i915_reset.
+	 */
+	if (!atomic_read(&execlists->tasklet.count))
+		tasklet_kill(&execlists->tasklet);
+	tasklet_disable(&execlists->tasklet);
+
+	/*
+	 * We're using worker to queue preemption requests from the tasklet in
+	 * GuC submission mode.
+	 * Even though tasklet was disabled, we may still have a worker queued.
+	 * Let's make sure that all workers scheduled before disabling the
+	 * tasklet are completed before continuing with the reset.
+	 */
+	if (engine->i915->guc.preempt_wq)
+		flush_workqueue(engine->i915->guc.preempt_wq);
+
+	return i915_gem_find_active_request(engine);
+}
+
 /*
  * Everything below here is concerned with setup & teardown, and is
  * therefore not part of the somewhat time-critical batch-submission
@@ -1235,6 +1273,7 @@ int intel_guc_submission_enable(struct intel_guc *guc)
 			&engine->execlists;
 
 		execlists->tasklet.func = guc_submission_tasklet;
+		engine->reset.prepare = guc_reset_prepare;
 		engine->park = guc_submission_park;
 		engine->unpark = guc_submission_unpark;
 
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index f662a9524233..e5a3ffbc273a 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1688,16 +1688,6 @@ execlists_reset_prepare(struct intel_engine_cs *engine)
 		tasklet_kill(&execlists->tasklet);
 	tasklet_disable(&execlists->tasklet);
 
-	/*
-	 * We're using worker to queue preemption requests from the tasklet in
-	 * GuC submission mode.
-	 * Even though tasklet was disabled, we may still have a worker queued.
-	 * Let's make sure that all workers scheduled before disabling the
-	 * tasklet are completed before continuing with the reset.
-	 */
-	if (engine->i915->guc.preempt_wq)
-		flush_workqueue(engine->i915->guc.preempt_wq);
-
 	return i915_gem_find_active_request(engine);
 }
 
@@ -2115,6 +2105,7 @@ static void execlists_set_default_submission(struct intel_engine_cs *engine)
 	engine->cancel_requests = execlists_cancel_requests;
 	engine->schedule = execlists_schedule;
 	engine->execlists.tasklet.func = execlists_submission_tasklet;
+	engine->reset.prepare = execlists_reset_prepare;
 
 	engine->park = NULL;
 	engine->unpark = NULL;
-- 
2.16.2

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