# \[PATCH net-next v8 03/11\] r8152: add rtl8157\_change\_mtu() for RTL8157 and RTL8159

- From: Chih Kai Hsu \<hidden\>
- Date: 2026-11-10 03:25:05 
- List: netdev
- Page: https://ratatoskr.run/netdev/2026/11/17902500
- Thread: https://ratatoskr.run/netdev/2026/11/17902506/t.md

```text
RTL8157 and RTL8159 used rtl8156_change_mtu(), which programs a fixed
MTPS_JUMBO. Per the datasheet they need an MTPS scaled from the
configured MTU instead: max_pkt_size / 64, at least 10K and capped
at 0xff.

Add rtl8157_change_mtu() for them. Since rtl8156_up() is shared with
these chips, have it call tp->rtl_ops.change_mtu() instead of
rtl8156_change_mtu() directly so each chip gets its own helper.

Fixes: fd3c7d080df5 ("r8152: Add support for the RTL8157 hardware")
Fixes: ad2a55b63b41 ("r8152: Add support for the RTL8159 chip")
Signed-off-by: Chih Kai Hsu <redacted>
---
 drivers/net/usb/r8152.c | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/drivers/net/usb/r8152.c b/drivers/net/usb/r8152.c
index bb4106f238a3a..1517753f843ef 100644
--- a/drivers/net/usb/r8152.c
+++ b/drivers/net/usb/r8152.c
@@ -6800,6 +6800,28 @@ static void rtl8156_change_mtu(struct r8152 *tp)
 		       ALIGN(rx_max_size + tp->tx_desc.size, 1024) / 16);
 }
 
+static void rtl8157_change_mtu(struct r8152 *tp)
+{
+	u32 max_pkt_size = mtu_to_size(tp->netdev->mtu);
+	u32 ocp_data;
+
+	ocp_write_word(tp, MCU_TYPE_PLA, PLA_RMS, max_pkt_size);
+
+	/* Use at least 10K for MTPS */
+	ocp_data = max_t(u32, max_pkt_size, 10 * 1024) / 64;
+
+	/* 16 * 1024 / 64 = 0x100, so the max is 0xff for 8 bits data */
+	ocp_data = min_t(u32, ocp_data, 0xff);
+
+	ocp_write_byte(tp, MCU_TYPE_PLA, PLA_MTPS, ocp_data);
+	r8156_fc_parameter(tp);
+
+	/* TX share fifo free credit full threshold */
+	ocp_write_word(tp, MCU_TYPE_PLA, PLA_TXFIFO_CTRL, 512 / 64);
+	ocp_write_word(tp, MCU_TYPE_PLA, PLA_TXFIFO_FULL,
+		       ALIGN(max_pkt_size + tp->tx_desc.size, 1024) / 16);
+}
+
 static void rtl8156_up(struct r8152 *tp)
 {
 	if (test_bit(RTL8152_INACCESSIBLE, &tp->flags))
@@ -6826,7 +6848,7 @@ static void rtl8156_up(struct r8152 *tp)
 
 	rtl_rx_vlan_en(tp, tp->netdev->features & NETIF_F_HW_VLAN_CTAG_RX);
 
-	rtl8156_change_mtu(tp);
+	tp->rtl_ops.change_mtu(tp);
 
 	switch (tp->version) {
 	case RTL_TEST_01:
@@ -9900,7 +9922,7 @@ static int rtl_ops_init(struct r8152 *tp)
 		ops->in_nway		= rtl8153_in_nway;
 		ops->hw_phy_cfg		= r8157_hw_phy_cfg;
 		ops->autosuspend_en	= rtl8157_runtime_enable;
-		ops->change_mtu		= rtl8156_change_mtu;
+		ops->change_mtu		= rtl8157_change_mtu;
 		tp->rx_buf_sz		= 32 * 1024;
 		tp->support_2500full	= 1;
 		tp->support_5000full	= 1;
@@ -9922,7 +9944,7 @@ static int rtl_ops_init(struct r8152 *tp)
 		ops->in_nway		= rtl8153_in_nway;
 		ops->hw_phy_cfg		= r8157_hw_phy_cfg;
 		ops->autosuspend_en	= rtl8157_runtime_enable;
-		ops->change_mtu		= rtl8156_change_mtu;
+		ops->change_mtu		= rtl8157_change_mtu;
 		tp->rx_buf_sz		= 48 * 1024;
 		tp->support_2500full	= 1;
 		tp->support_5000full	= 1;
-- 
2.34.1

```