nvme: refactor set_queue_count

BugLink: http://bugs.launchpad.net/bugs/1531539

Split out a helper that just issues the Set Features and interprets the
result which can go to common code, and document why we are ignoring
non-timeout error returns in the PCIe driver.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
(cherry picked from commit 9a0be7ab)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/nvme/host/core.c

@@ -327,6 +327,22 @@ int nvme_get_log_page(struct nvme_ctrl *dev, struct nvme_smart_log **log)
 	return error;
 }
 
+int nvme_set_queue_count(struct nvme_ctrl *ctrl, int *count)
+{
+	u32 q_count = (*count - 1) | ((*count - 1) << 16);
+	u32 result;
+	int status, nr_io_queues;
+
+	status = nvme_set_features(ctrl, NVME_FEAT_NUM_QUEUES, q_count, 0,
+			&result);
+	if (status)
+		return status;
+
+	nr_io_queues = min(result & 0xffff, result >> 16) + 1;
+	*count = min(*count, nr_io_queues);
+	return 0;
+}
+
 static int nvme_submit_io(struct nvme_ns *ns, struct nvme_user_io __user *uio)
 {
 	struct nvme_user_io io;

drivers/nvme/host/nvme.h

@@ -232,6 +232,7 @@ int nvme_get_features(struct nvme_ctrl *dev, unsigned fid, unsigned nsid,
 			dma_addr_t dma_addr, u32 *result);
 int nvme_set_features(struct nvme_ctrl *dev, unsigned fid, unsigned dword11,
 			dma_addr_t dma_addr, u32 *result);
+int nvme_set_queue_count(struct nvme_ctrl *ctrl, int *count);
 
 extern spinlock_t dev_list_lock;
 

drivers/nvme/host/pci.c

@@ -1559,23 +1559,6 @@ static void nvme_create_io_queues(struct nvme_dev *dev)
 		}
 }
 
-static int set_queue_count(struct nvme_dev *dev, int count)
-{
-	int status;
-	u32 result;
-	u32 q_count = (count - 1) | ((count - 1) << 16);
-
-	status = nvme_set_features(&dev->ctrl, NVME_FEAT_NUM_QUEUES, q_count, 0,
-								&result);
-	if (status < 0)
-		return status;
-	if (status > 0) {
-		dev_err(dev->dev, "Could not set queue count (%d)\n", status);
-		return 0;
-	}
-	return min(result & 0xffff, result >> 16) + 1;
-}
-
 static void __iomem *nvme_map_cmb(struct nvme_dev *dev)
 {
 	u64 szu, size, offset;
@@ -1640,11 +1623,20 @@ static int nvme_setup_io_queues(struct nvme_dev *dev)
 	int result, i, vecs, nr_io_queues, size;
 
 	nr_io_queues = num_possible_cpus();
-	result = set_queue_count(dev, nr_io_queues);
-	if (result <= 0)
+	result = nvme_set_queue_count(&dev->ctrl, &nr_io_queues);
+	if (result < 0)
 		return result;
-	if (result < nr_io_queues)
-		nr_io_queues = result;
+
+	/*
+	 * Degraded controllers might return an error when setting the queue
+	 * count.  We still want to be able to bring them online and offer
+	 * access to the admin queue, as that might be only way to fix them up.
+	 */
+	if (result > 0) {
+		dev_err(dev->dev, "Could not set queue count (%d)\n", result);
+		nr_io_queues = 0;
+		result = 0;
+	}
 
 	if (dev->cmb && NVME_CMB_SQS(dev->cmbsz)) {
 		result = nvme_cmb_qdepth(dev, nr_io_queues,