IB/mlx5: Fix retrieval of index to first hi class bfreg

First the function retrieving the index of the first hi latency class
blue flame register. High latency class bfregs are located right above
medium latency class bfregs.

Fixes: c1be523 ('IB/mlx5: Fix micro UAR allocator')
Signed-off-by: Eli Cohen <eli@mellanox.com>
Reviewed-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

drivers/infiniband/hw/mlx5/qp.c

@@ -490,12 +490,21 @@ static int next_bfreg(int n)
 	return n;
 }
 
+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
+	 * regular 64 bit doorbells, we do not need a lock for maintaiing
+	 * "odd/even" order
+	 */
+	NUM_NON_BLUE_FLAME_BFREGS = 1,
+};
+
 static int num_med_bfreg(struct mlx5_bfreg_info *bfregi)
 {
 	int n;
 
 	n = bfregi->num_uars * MLX5_NON_FP_BFREGS_PER_UAR -
-		bfregi->num_low_latency_bfregs - 1;
+		bfregi->num_low_latency_bfregs - NUM_NON_BLUE_FLAME_BFREGS;
 
 	return n >= 0 ? n : 0;
 }
@@ -508,17 +517,9 @@ static int max_bfregi(struct mlx5_bfreg_info *bfregi)
 static int first_hi_bfreg(struct mlx5_bfreg_info *bfregi)
 {
 	int med;
-	int i;
-	int t;
 
 	med = num_med_bfreg(bfregi);
-	for (t = 0, i = first_med_bfreg();; i = next_bfreg(i)) {
-		t++;
-		if (t == med)
-			return next_bfreg(i);
-	}
-
-	return 0;
+	return next_bfreg(med);
 }
 
 static int alloc_high_class_bfreg(struct mlx5_bfreg_info *bfregi)
@@ -544,6 +545,8 @@ static int alloc_med_class_bfreg(struct mlx5_bfreg_info *bfregi)
 	for (i = first_med_bfreg(); i < first_hi_bfreg(bfregi); i = next_bfreg(i)) {
 		if (bfregi->count[i] < bfregi->count[minidx])
 			minidx = i;
+		if (!bfregi->count[minidx])
+			break;
 	}
 
 	bfregi->count[minidx]++;
@@ -558,6 +561,7 @@ static int alloc_bfreg(struct mlx5_bfreg_info *bfregi,
 	mutex_lock(&bfregi->lock);
 	switch (lat) {
 	case MLX5_IB_LATENCY_CLASS_LOW:
+		BUILD_BUG_ON(NUM_NON_BLUE_FLAME_BFREGS != 1);
 		bfregn = 0;
 		bfregi->count[bfregn]++;
 		break;