RDMA/mlx5: Don't assume that medium blueFlame register exists

User can leave system without medium BlueFlames registers,
however the code assumed that at least one such register exists.

This patch fixes that assumption.

Fixes: c1be5232d21d ("IB/mlx5: Fix micro UAR allocator")
Reported-by: Rohit Zambre <rzambre@uci.edu>
Signed-off-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/mlx5/qp.c

@@ -484,11 +484,6 @@ static int qp_has_rq(struct ib_qp_init_attr *attr)
 	return 1;
 }
 
-static int first_med_bfreg(void)
-{
-	return 1;
-}
-
 enum {
 	/* this is the first blue flame register in the array of bfregs assigned
 	 * to a processes. Since we do not use it for blue flame but rather
@@ -514,6 +509,12 @@ static int num_med_bfreg(struct mlx5_ib_dev *dev,
 	return n >= 0 ? n : 0;
 }
 
+static int first_med_bfreg(struct mlx5_ib_dev *dev,
+			   struct mlx5_bfreg_info *bfregi)
+{
+	return num_med_bfreg(dev, bfregi) ? 1 : -ENOMEM;
+}
+
 static int first_hi_bfreg(struct mlx5_ib_dev *dev,
 			  struct mlx5_bfreg_info *bfregi)
 {
@@ -541,10 +542,13 @@ static int alloc_high_class_bfreg(struct mlx5_ib_dev *dev,
 static int alloc_med_class_bfreg(struct mlx5_ib_dev *dev,
 				 struct mlx5_bfreg_info *bfregi)
 {
-	int minidx = first_med_bfreg();
+	int minidx = first_med_bfreg(dev, bfregi);
 	int i;
 
-	for (i = first_med_bfreg(); i < first_hi_bfreg(dev, bfregi); i++) {
+	if (minidx < 0)
+		return minidx;
+
+	for (i = minidx; i < first_hi_bfreg(dev, bfregi); i++) {
 		if (bfregi->count[i] < bfregi->count[minidx])
 			minidx = i;
 		if (!bfregi->count[minidx])