[PATCH v1 3/3] net: mtk_eth: an8855: sync SerDes analog tuning with Linux driver

[Mikhail Zhilkin <csharper2005@gmail.com>]

Port the TX FIR (TX Eye) and RX CDR (RX Jitter Tolerance) analog
tuning parameters from the upstream Linux Airoha AN8855 DSA driver
(drivers/net/dsa/airoha/an8855.c).

The default U-Boot configuration omits these register writes, leaving
the SerDes with inferior default drive characteristics. On hardware
iterations with minor silicon or trace variances, this marginal signal
integrity leads to severe packet loss (50-60%) during TFTP recovery
over the 2500Base-X link. Explicitly configuring AN8855_INTF_CTRL_10,
AN8855_INTF_CTRL_11, and AN8855_RG_QP_CDR_LPF_BOT_LIM ensures a
stable physical link across boards.

Signed-off-by: Mikhail Zhilkin <csharper2005@gmail.com>
---
 drivers/net/mtk_eth/an8855.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/drivers/net/mtk_eth/an8855.c b/drivers/net/mtk_eth/an8855.c
index 513f4534701..f8f004e0914 100644
--- a/drivers/net/mtk_eth/an8855.c
+++ b/drivers/net/mtk_eth/an8855.c
@@ -96,6 +96,8 @@
 #define AN8855_SS_LCPLL_TDC_PCW_1		(AN8855_QP_PMA_TOP_BASE + 0x248)
 #define AN8855_INTF_CTRL_8			(AN8855_QP_PMA_TOP_BASE + 0x320)
 #define AN8855_INTF_CTRL_9			(AN8855_QP_PMA_TOP_BASE + 0x324)
+#define AN8855_INTF_CTRL_10			(AN8855_QP_PMA_TOP_BASE + 0x328)
+#define AN8855_INTF_CTRL_11			(AN8855_QP_PMA_TOP_BASE + 0x32c)
 #define AN8855_PLL_CTRL_0			(AN8855_QP_PMA_TOP_BASE + 0x400)
 #define AN8855_PLL_CTRL_2			(AN8855_QP_PMA_TOP_BASE + 0x408)
 #define AN8855_PLL_CTRL_3			(AN8855_QP_PMA_TOP_BASE + 0x40c)
@@ -113,6 +115,7 @@
 #define AN8855_QP_ANA_CSR_BASE			0x1022f000
 #define AN8855_RG_QP_RX_DAC_EN			(AN8855_QP_ANA_CSR_BASE + 0x00)
 #define AN8855_RG_QP_RXAFE_RESERVE		(AN8855_QP_ANA_CSR_BASE + 0x04)
+#define AN8855_RG_QP_CDR_LPF_BOT_LIM		(AN8855_QP_ANA_CSR_BASE + 0x08)
 #define AN8855_RG_QP_CDR_LPF_MJV_LIM		(AN8855_QP_ANA_CSR_BASE + 0x0c)
 #define AN8855_RG_QP_CDR_LPF_SETVALUE		(AN8855_QP_ANA_CSR_BASE + 0x14)
 #define AN8855_RG_QP_CDR_PR_CKREF_DIV1		(AN8855_QP_ANA_CSR_BASE + 0x18)
@@ -678,6 +681,28 @@ static int an8855_port_sgmii_init(struct an8855_switch_priv *priv, u32 port)
 	an8855_reg_write(priv, AN8855_MSG_RX_LIK_STS_0, 0x01010107);
 	an8855_reg_write(priv, AN8855_MSG_RX_LIK_STS_2, 0x00000EEF);
 
+	/* TX FIR - improve TX EYE */
+	an8855_reg_read(priv, AN8855_INTF_CTRL_10, &val);
+	val &= ~(0x1f << 24);
+	val |= (0x04 << 24);
+	val &= ~(0x1f << 16);
+	val |= (0x00 << 16);
+	val |= BIT(29) | BIT(21);
+	an8855_reg_write(priv, AN8855_INTF_CTRL_10, val);
+
+	an8855_reg_read(priv, AN8855_INTF_CTRL_11, &val);
+	val &= ~(0x3f << 0);
+	val |= BIT(6);
+	an8855_reg_write(priv, AN8855_INTF_CTRL_11, val);
+
+	/* RX CDR - improve RX Jitter Tolerance */
+	an8855_reg_read(priv, AN8855_RG_QP_CDR_LPF_BOT_LIM, &val);
+	val &= ~(0x7 << 24);
+	val |= (0x5 << 24);
+	val &= ~(0x7 << 20);
+	val |= (0x5 << 20);
+	an8855_reg_write(priv, AN8855_RG_QP_CDR_LPF_BOT_LIM, val);
+
 	return 0;
 }
 
-- 
2.53.0