isdn: hisax: fix frame calculation

Difference of unsigned values is also unsigned so it does not make
sense to check its sign.

The problem has been detected using proposed semantic patch
scripts/coccinelle/tests/unsigned_lesser_than_zero.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2038576

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 5 deletions

diff --git a/drivers/isdn/hisax/hfc4s8s_l1.c b/drivers/isdn/hisax/hfc4s8s_l1.c
index 0e5d673871c0..9600cd771f1a 100644
--- a/drivers/isdn/hisax/hfc4s8s_l1.c
+++ b/drivers/isdn/hisax/hfc4s8s_l1.c
@@ -646,14 +646,14 @@ rx_d_frame(struct hfc4s8s_l1 *l1p, int ech)
 
                 f1 = Read_hfc8_stable(l1p->hw, A_F1);
                 f2 = Read_hfc8(l1p->hw, A_F2);
-                df = f1 - f2;
-                if ((f1 - f2) < 0)
-                        df = f1 - f2 + MAX_F_CNT + 1;
 
+                if (f1 < f2)
+                        df = MAX_F_CNT + 1 + f1 - f2;
+                else
+                        df = f1 - f2;
 
-                if (!df) {
+                if (!df)
                         return; /* no complete frame in fifo */
-                }
 
                 z1 = Read_hfc16_stable(l1p->hw, A_Z1);
                 z2 = Read_hfc16(l1p->hw, A_Z2);