From a97b786bfac6929223cc9a01683effe84146e394 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Wed, 25 Mar 2020 13:00:59 +0000
Subject: drm/i915/gt: Stage the transfer of the virtual breadcrumb
Git-commit: a97b786bfac6929223cc9a01683effe84146e394
Patch-mainline: v5.7-rc1
References: bsc#1152489

We move the virtual breadcrumb from one physical engine to the next, if
the next virtual request is scheduled on a new physical engine. Since
the virtual context can only be in one signal queue, we need it to track
the current physical engine for the new breadcrumbs. However, to move
the list we need both breadcrumb locks -- and since we cannot take both
at the same time (unless we are careful and always ensure consistent
ordering) stage the movement of the signaler via the current virtual
request.

Closes: https://gitlab.freedesktop.org/drm/intel/issues/1510
Fixes: 6d06779e8672 ("drm/i915: Load balancing across a virtual engine")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200325130059.30600-1-chris@chris-wilson.co.uk
(cherry picked from commit 6c81e21a4742385c00713137c6fdcade0412e93c)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/gpu/drm/i915/gt/intel_lrc.c |   20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -907,7 +907,7 @@ static bool virtual_matches(const struct
 }
 
 static void virtual_xfer_breadcrumbs(struct virtual_engine *ve,
-				     struct intel_engine_cs *engine)
+				     struct i915_request *rq)
 {
 	struct intel_engine_cs *old = ve->siblings[0];
 
@@ -915,9 +915,19 @@ static void virtual_xfer_breadcrumbs(str
 
 	spin_lock(&old->breadcrumbs.irq_lock);
 	if (!list_empty(&ve->context.signal_link)) {
-		list_move_tail(&ve->context.signal_link,
-			       &engine->breadcrumbs.signalers);
-		intel_engine_queue_breadcrumbs(engine);
+		list_del_init(&ve->context.signal_link);
+
+		/*
+		 * We cannot acquire the new engine->breadcrumbs.irq_lock
+		 * (as we are holding a breadcrumbs.irq_lock already),
+		 * so attach this request to the signaler on submission.
+		 * The queued irq_work will occur when we finally drop
+		 * the engine->active.lock after dequeue.
+		 */
+		set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &rq->fence.flags);
+
+		/* Also transfer the pending irq_work for the old breadcrumb. */
+		intel_engine_signal_breadcrumbs(rq->engine);
 	}
 	spin_unlock(&old->breadcrumbs.irq_lock);
 }
@@ -1221,7 +1231,7 @@ static void execlists_dequeue(struct int
 				virtual_update_register_offsets(regs, engine);
 
 				if (!list_empty(&ve->context.signals))
-					virtual_xfer_breadcrumbs(ve, engine);
+					virtual_xfer_breadcrumbs(ve, rq);
 
 				/*
 				 * Move the bound engine to the top of the list