Prepare to allow the execlists submission to be run from underneath a
hardirq timer context (and not just the current softirq context) as is
required for fast preemption resets and context switches.

Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_lrc.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index f9f4064dec0e..56d60e830d11 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -554,7 +554,7 @@ static void inject_preempt_context(struct intel_engine_cs 
*engine)
        execlists_set_active(&engine->execlists, EXECLISTS_ACTIVE_PREEMPT);
 }
 
-static void execlists_dequeue(struct intel_engine_cs *engine)
+static bool __execlists_dequeue(struct intel_engine_cs *engine)
 {
        struct intel_engine_execlists * const execlists = &engine->execlists;
        struct execlist_port *port = execlists->port;
@@ -564,6 +564,8 @@ static void execlists_dequeue(struct intel_engine_cs 
*engine)
        struct rb_node *rb;
        bool submit = false;
 
+       lockdep_assert_held(&engine->timeline.lock);
+
        /* Hardware submission is through 2 ports. Conceptually each port
         * has a (RING_START, RING_HEAD, RING_TAIL) tuple. RING_START is
         * static for a context, and unique to each, so we only execute
@@ -585,7 +587,6 @@ static void execlists_dequeue(struct intel_engine_cs 
*engine)
         * and context switches) submission.
         */
 
-       spin_lock_irq(&engine->timeline.lock);
        rb = execlists->first;
        GEM_BUG_ON(rb_first(&execlists->queue) != rb);
 
@@ -745,12 +746,24 @@ static void execlists_dequeue(struct intel_engine_cs 
*engine)
        GEM_BUG_ON(execlists->first && !port_isset(execlists->port));
 
 unlock:
-       spin_unlock_irq(&engine->timeline.lock);
-
-       if (submit) {
+       if (last)
                execlists_user_begin(execlists, execlists->port);
+
+       return submit;
+}
+
+static void execlists_dequeue(struct intel_engine_cs *engine)
+{
+       struct intel_engine_execlists * const execlists = &engine->execlists;
+       unsigned long flags;
+       bool submit;
+
+       spin_lock_irqsave(&engine->timeline.lock, flags);
+       submit = __execlists_dequeue(engine);
+       spin_unlock_irqrestore(&engine->timeline.lock, flags);
+
+       if (submit)
                execlists_submit_ports(engine);
-       }
 
        GEM_BUG_ON(port_isset(execlists->port) &&
                   !execlists_is_active(execlists, EXECLISTS_ACTIVE_USER));
-- 
2.17.0

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