net: hns3: fix shaper parameter algorithm

Currently when hns3 driver configures the tm shaper to limit
bandwidth below 20Mbit using the parameters calculated by
hclge_shaper_para_calc(), the actual bandwidth limited by tm
hardware module is not accurate enough, for example, 1.28 Mbit
when the user is configuring 1 Mbit.

This patch adjusts the ir_calc to be closer to ir, and
always calculate the ir_b parameter when user is configuring
a small bandwidth. Also, removes an unnecessary parenthesis
when calculating denominator.

Fixes: 84844054 ("net: hns3: Add support of TX Scheduler & Shaper to HNS3 driver")
Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/hisilicon/hns3/hns3pf/hclge_tm.c

@@ -81,16 +81,13 @@ static int hclge_shaper_para_calc(u32 ir, u8 shaper_level,
 		return 0;
 	} else if (ir_calc > ir) {
 		/* Increasing the denominator to select ir_s value */
-		while (ir_calc > ir) {
+		while (ir_calc >= ir && ir) {
 			ir_s_calc++;
 			ir_calc = DIVISOR_IR_B_126 / (tick * (1 << ir_s_calc));
 		}
 
-		if (ir_calc == ir)
-			*ir_b = 126;
-		else
-			*ir_b = (ir * tick * (1 << ir_s_calc) +
-				 (DIVISOR_CLK >> 1)) / DIVISOR_CLK;
+		*ir_b = (ir * tick * (1 << ir_s_calc) + (DIVISOR_CLK >> 1)) /
+			DIVISOR_CLK;
 	} else {
 		/* Increasing the numerator to select ir_u value */
 		u32 numerator;
@@ -104,7 +101,7 @@ static int hclge_shaper_para_calc(u32 ir, u8 shaper_level,
 		if (ir_calc == ir) {
 			*ir_b = 126;
 		} else {
-			u32 denominator = (DIVISOR_CLK * (1 << --ir_u_calc));
+			u32 denominator = DIVISOR_CLK * (1 << --ir_u_calc);
 			*ir_b = (ir * tick + (denominator >> 1)) / denominator;
 		}
 	}