NVMe: add blk polling support

Add nvme_poll(), which will check a specific completion queue for
command completions. Wire that up to the new block layer poll
mechanism.
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Keith Busch <keith.busch@intel.com>

drivers/nvme/host/pci.c

@@ -90,7 +90,7 @@ static struct class *nvme_class;
 
 static int __nvme_reset(struct nvme_dev *dev);
 static int nvme_reset(struct nvme_dev *dev);
-static int nvme_process_cq(struct nvme_queue *nvmeq);
+static void nvme_process_cq(struct nvme_queue *nvmeq);
 static void nvme_dead_ctrl(struct nvme_dev *dev);
 
 struct async_cmd_info {
@@ -935,7 +935,7 @@ static int nvme_queue_rq(struct blk_mq_hw_ctx *hctx,
 	return BLK_MQ_RQ_QUEUE_BUSY;
 }
 
-static int nvme_process_cq(struct nvme_queue *nvmeq)
+static void __nvme_process_cq(struct nvme_queue *nvmeq, unsigned int *tag)
 {
 	u16 head, phase;
 
@@ -953,6 +953,8 @@ static int nvme_process_cq(struct nvme_queue *nvmeq)
 			head = 0;
 			phase = !phase;
 		}
+		if (tag && *tag == cqe.command_id)
+			*tag = -1;
 		ctx = nvme_finish_cmd(nvmeq, cqe.command_id, &fn);
 		fn(nvmeq, ctx, &cqe);
 	}
@@ -964,14 +966,18 @@ static int nvme_process_cq(struct nvme_queue *nvmeq)
 	 * a big problem.
 	 */
 	if (head == nvmeq->cq_head && phase == nvmeq->cq_phase)
-		return 0;
+		return;
 
 	writel(head, nvmeq->q_db + nvmeq->dev->db_stride);
 	nvmeq->cq_head = head;
 	nvmeq->cq_phase = phase;
 
 	nvmeq->cqe_seen = 1;
-	return 1;
+}
+
+static void nvme_process_cq(struct nvme_queue *nvmeq)
+{
+	__nvme_process_cq(nvmeq, NULL);
 }
 
 static irqreturn_t nvme_irq(int irq, void *data)
@@ -995,6 +1001,23 @@ static irqreturn_t nvme_irq_check(int irq, void *data)
 	return IRQ_WAKE_THREAD;
 }
 
+static int nvme_poll(struct blk_mq_hw_ctx *hctx, unsigned int tag)
+{
+	struct nvme_queue *nvmeq = hctx->driver_data;
+
+	if ((le16_to_cpu(nvmeq->cqes[nvmeq->cq_head].status) & 1) ==
+	    nvmeq->cq_phase) {
+		spin_lock_irq(&nvmeq->q_lock);
+		__nvme_process_cq(nvmeq, &tag);
+		spin_unlock_irq(&nvmeq->q_lock);
+
+		if (tag == -1)
+			return 1;
+	}
+
+	return 0;
+}
+
 /*
  * Returns 0 on success.  If the result is negative, it's a Linux error code;
  * if the result is positive, it's an NVM Express status code
@@ -1654,6 +1677,7 @@ static struct blk_mq_ops nvme_mq_ops = {
 	.init_hctx	= nvme_init_hctx,
 	.init_request	= nvme_init_request,
 	.timeout	= nvme_timeout,
+	.poll		= nvme_poll,
 };
 
 static void nvme_dev_remove_admin(struct nvme_dev *dev)