drm/i915/guc: Make wq_lock irq-safe

Following the use of dma_fence_signal() from within our interrupt
handler, we need to make guc->wq_lock also irq-safe. This was done
previously as part of the guc scheduler patch (which also started
mixing our fences with the interrupt handler), but is now required to
fix the current guc submission backend.

v4: Document that __i915_guc_submit is always under an irq disabled
section
v5: Move wq_rsvd adjustment to its own function

Fixes: 67b807a89230 ("drm/i915: Delay disabling the user interrupt for breadcrumbs")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170228112803.11646-2-chris@chris-wilson.co.uk
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

drivers/gpu/drm/i915/i915_guc_submission.c

@@ -348,7 +348,7 @@ int i915_guc_wq_reserve(struct drm_i915_gem_request *request)
 	u32 freespace;
 	int ret;
 
-	spin_lock(&client->wq_lock);
+	spin_lock_irq(&client->wq_lock);
 	freespace = CIRC_SPACE(client->wq_tail, desc->head, client->wq_size);
 	freespace -= client->wq_rsvd;
 	if (likely(freespace >= wqi_size)) {
@@ -358,21 +358,27 @@ int i915_guc_wq_reserve(struct drm_i915_gem_request *request)
 		client->no_wq_space++;
 		ret = -EAGAIN;
 	}
-	spin_unlock(&client->wq_lock);
+	spin_unlock_irq(&client->wq_lock);
 
 	return ret;
 }
 
+static void guc_client_update_wq_rsvd(struct i915_guc_client *client, int size)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&client->wq_lock, flags);
+	client->wq_rsvd += size;
+	spin_unlock_irqrestore(&client->wq_lock, flags);
+}
+
 void i915_guc_wq_unreserve(struct drm_i915_gem_request *request)
 {
-	const size_t wqi_size = sizeof(struct guc_wq_item);
+	const int wqi_size = sizeof(struct guc_wq_item);
 	struct i915_guc_client *client = request->i915->guc.execbuf_client;
 
 	GEM_BUG_ON(READ_ONCE(client->wq_rsvd) < wqi_size);
-
-	spin_lock(&client->wq_lock);
-	client->wq_rsvd -= wqi_size;
-	spin_unlock(&client->wq_lock);
+	guc_client_update_wq_rsvd(client, -wqi_size);
 }
 
 /* Construct a Work Item and append it to the GuC's Work Queue */
@@ -511,6 +517,9 @@ static void __i915_guc_submit(struct drm_i915_gem_request *rq)
 	struct i915_guc_client *client = guc->execbuf_client;
 	int b_ret;
 
+	/* We are always called with irqs disabled */
+	GEM_BUG_ON(!irqs_disabled());
+
 	spin_lock(&client->wq_lock);
 	guc_wq_item_append(client, rq);
 
@@ -945,16 +954,19 @@ int i915_guc_submission_enable(struct drm_i915_private *dev_priv)
 
 	/* Take over from manual control of ELSP (execlists) */
 	for_each_engine(engine, dev_priv, id) {
+		const int wqi_size = sizeof(struct guc_wq_item);
 		struct drm_i915_gem_request *rq;
 
 		engine->submit_request = i915_guc_submit;
 		engine->schedule = NULL;
 
 		/* Replay the current set of previously submitted requests */
+		spin_lock_irq(&engine->timeline->lock);
 		list_for_each_entry(rq, &engine->timeline->requests, link) {
-			client->wq_rsvd += sizeof(struct guc_wq_item);
+			guc_client_update_wq_rsvd(client, wqi_size);
 			__i915_guc_submit(rq);
 		}
+		spin_unlock_irq(&engine->timeline->lock);
 	}
 
 	return 0;