net: dsa: microchip: add support for credit based shaper

KSZ9477, KSZ9567, KSZ9563, KSZ8563 and LAN937x supports Credit based
shaper. To differentiate the chip supporting cbs, tc_cbs_supported
flag is introduced in ksz_chip_data.
And KSZ series has 16bit Credit increment registers whereas LAN937x has
24bit register. The value to be programmed in the credit increment is
determined using the successive multiplication method to convert decimal
fraction to hexadecimal fraction.
For example: if idleslope is 10000 and sendslope is -90000, then
bandwidth is 10000 - (-90000) = 100000.
The 10% bandwidth of 100Mbps means 10/100 = 0.1(decimal). This value has
to be converted to hexa.
1) 0.1 * 16 = 1.6  --> fraction 0.6 Carry = 1 (MSB)
2) 0.6 * 16 = 9.6  --> fraction 0.6 Carry = 9
3) 0.6 * 16 = 9.6  --> fraction 0.6 Carry = 9
4) 0.6 * 16 = 9.6  --> fraction 0.6 Carry = 9
5) 0.6 * 16 = 9.6  --> fraction 0.6 Carry = 9
6) 0.6 * 16 = 9.6  --> fraction 0.6 Carry = 9 (LSB)
Now 0.1(decimal) becomes 0.199999(Hex).
If it is LAN937x, 24 bit value will be programmed to Credit Inc
register, 0x199999. For others 16 bit value will be prgrammed, 0x1999.

Signed-off-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/net/dsa/microchip/lan937x_main.c b/drivers/net/dsa/microchip/lan937x_main.c
index 923388f87996..399a3905e6ca 100644
--- a/drivers/net/dsa/microchip/lan937x_main.c
+++ b/drivers/net/dsa/microchip/lan937x_main.c
@@ -340,6 +340,11 @@ void lan937x_setup_rgmii_delay(struct ksz_device *dev, int port)
 	}
 }
 
+int lan937x_tc_cbs_set_cinc(struct ksz_device *dev, int port, u32 val)
+{
+	return ksz_pwrite32(dev, port, REG_PORT_MTI_CREDIT_INCREMENT, val);
+}
+
 int lan937x_switch_init(struct ksz_device *dev)
 {
 	dev->port_mask = (1 << dev->info->port_cnt) - 1;