drm/i915: kill waiting_seqno

The waiting_seqno is not terribly useful, and as such we can remove it
so that we'll be able to extract lockless code.

v2: Keep the information for error_state (Chris)
Check if ring is initialized in hangcheck (Chris)
Capture the waiting ring (Chris)
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
[danvet: add some bikeshed to clarify a comment.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -414,8 +414,6 @@ static void i915_ring_seqno_info(struct seq_file *m,
 	if (ring->get_seqno) {
 		seq_printf(m, "Current sequence (%s): %d\n",
 			   ring->name, ring->get_seqno(ring));
-		seq_printf(m, "Waiter sequence (%s):  %d\n",
-			   ring->name, ring->waiting_seqno);
 		seq_printf(m, "IRQ sequence (%s):     %d\n",
 			   ring->name, ring->irq_seqno);
 	}
@@ -687,6 +685,7 @@ static void i915_ring_error_state(struct seq_file *m,
 			   error->semaphore_mboxes[ring][1]);
 	}
 	seq_printf(m, "  seqno: 0x%08x\n", error->seqno[ring]);
+	seq_printf(m, "  waiting: %s\n", yesno(error->waiting[ring]));
 	seq_printf(m, "  ring->head: 0x%08x\n", error->cpu_ring_head[ring]);
 	seq_printf(m, "  ring->tail: 0x%08x\n", error->cpu_ring_tail[ring]);
 }

drivers/gpu/drm/i915/i915_drv.h

@@ -174,6 +174,7 @@ struct drm_i915_error_state {
 	u32 eir;
 	u32 pgtbl_er;
 	u32 ier;
+	bool waiting[I915_NUM_RINGS];
 	u32 pipestat[I915_MAX_PIPES];
 	u32 tail[I915_NUM_RINGS];
 	u32 head[I915_NUM_RINGS];

drivers/gpu/drm/i915/i915_gem.c

@@ -1864,7 +1864,6 @@ i915_wait_request(struct intel_ring_buffer *ring,
 	if (!i915_seqno_passed(ring->get_seqno(ring), seqno)) {
 		trace_i915_gem_request_wait_begin(ring, seqno);
 
-		ring->waiting_seqno = seqno;
 		if (ring->irq_get(ring)) {
 			if (dev_priv->mm.interruptible)
 				ret = wait_event_interruptible(ring->irq_queue,
@@ -1880,7 +1879,6 @@ i915_wait_request(struct intel_ring_buffer *ring,
 							     seqno) ||
 					   atomic_read(&dev_priv->mm.wedged), 3000))
 			ret = -EBUSY;
-		ring->waiting_seqno = 0;
 
 		trace_i915_gem_request_wait_end(ring, seqno);
 	}

drivers/gpu/drm/i915/i915_irq.c

@@ -1031,6 +1031,7 @@ static void i915_record_ring_state(struct drm_device *dev,
 		error->instdone[ring->id] = I915_READ(INSTDONE);
 	}
 
+	error->waiting[ring->id] = waitqueue_active(&ring->irq_queue);
 	error->instpm[ring->id] = I915_READ(RING_INSTPM(ring->mmio_base));
 	error->seqno[ring->id] = ring->get_seqno(ring);
 	error->acthd[ring->id] = intel_ring_get_active_head(ring);
@@ -1708,14 +1709,17 @@ ring_last_seqno(struct intel_ring_buffer *ring)
 
 static bool i915_hangcheck_ring_idle(struct intel_ring_buffer *ring, bool *err)
 {
+	/* We don't check whether the ring even exists before calling this
+	 * function. Hence check whether it's initialized. */
+	if (ring->obj == NULL)
+		return true;
+
 	if (list_empty(&ring->request_list) ||
 	    i915_seqno_passed(ring->get_seqno(ring), ring_last_seqno(ring))) {
 		/* Issue a wake-up to catch stuck h/w. */
-		if (ring->waiting_seqno && waitqueue_active(&ring->irq_queue)) {
-			DRM_ERROR("Hangcheck timer elapsed... %s idle [waiting on %d, at %d], missed IRQ?\n",
-				  ring->name,
-				  ring->waiting_seqno,
-				  ring->get_seqno(ring));
+		if (waitqueue_active(&ring->irq_queue)) {
+			DRM_ERROR("Hangcheck timer elapsed... %s idle\n",
+				  ring->name);
 			wake_up_all(&ring->irq_queue);
 			*err = true;
 		}

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -60,7 +60,6 @@ struct  intel_ring_buffer {
 	u32		irq_enable_mask;	/* bitmask to enable ring interrupt */
 	u32		irq_seqno;		/* last seq seem at irq time */
 	u32		trace_irq_seqno;
-	u32		waiting_seqno;
 	u32		sync_seqno[I915_NUM_RINGS-1];
 	bool __must_check (*irq_get)(struct intel_ring_buffer *ring);
 	void		(*irq_put)(struct intel_ring_buffer *ring);