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

commit 0b80c14f upstream.

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: c1be5232 ('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>
[bwh: Backported to 3.16:
 - s/bfreg/uuar/g
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/infiniband/hw/mlx5/qp.c

@@ -367,12 +367,21 @@ static int next_uuar(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_uuar(struct mlx5_uuar_info *uuari)
 {
 	int n;
 
 	n = uuari->num_uars * MLX5_NON_FP_BF_REGS_PER_PAGE -
-		uuari->num_low_latency_uuars - 1;
+		uuari->num_low_latency_uuars - NUM_NON_BLUE_FLAME_BFREGS;
 
 	return n >= 0 ? n : 0;
 }
@@ -385,17 +394,9 @@ static int max_uuari(struct mlx5_uuar_info *uuari)
 static int first_hi_uuar(struct mlx5_uuar_info *uuari)
 {
 	int med;
-	int i;
-	int t;
 
 	med = num_med_uuar(uuari);
-	for (t = 0, i = first_med_uuar();; i = next_uuar(i)) {
-		t++;
-		if (t == med)
-			return next_uuar(i);
-	}
-
-	return 0;
+	return next_uuar(med);
 }
 
 static int alloc_high_class_uuar(struct mlx5_uuar_info *uuari)
@@ -421,6 +422,8 @@ static int alloc_med_class_uuar(struct mlx5_uuar_info *uuari)
 	for (i = first_med_uuar(); i < first_hi_uuar(uuari); i = next_uuar(i)) {
 		if (uuari->count[i] < uuari->count[minidx])
 			minidx = i;
+		if (!uuari->count[minidx])
+			break;
 	}
 
 	uuari->count[minidx]++;
@@ -435,6 +438,7 @@ static int alloc_uuar(struct mlx5_uuar_info *uuari,
 	mutex_lock(&uuari->lock);
 	switch (lat) {
 	case MLX5_IB_LATENCY_CLASS_LOW:
+		BUILD_BUG_ON(NUM_NON_BLUE_FLAME_BFREGS != 1);
 		uuarn = 0;
 		uuari->count[uuarn]++;
 		break;