diff --git a/MAINTAINERS b/MAINTAINERS
index 4b713407f887e..8a6b74bfe5560 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -13048,6 +13048,13 @@ L:	netdev@vger.kernel.org
 S:	Maintained
 F:	drivers/net/ethernet/mediatek/
 
+MEDIATEK ETHERNET PCS DRIVER
+M:	Daniel Golle <daniel@makrotopia.org>
+L:	netdev@vger.kernel.org
+S:	Maintained
+F:	drivers/net/pcs/pcs-mtk-lynxi.c
+F:	include/linux/pcs/pcs-mtk-lynxi.h
+
 MEDIATEK I2C CONTROLLER DRIVER
 M:	Qii Wang <qii.wang@mediatek.com>
 L:	linux-i2c@vger.kernel.org
diff --git a/drivers/net/pcs/Kconfig b/drivers/net/pcs/Kconfig
index 6e7e6c346a3ec..7c34fb7cbf7b4 100644
--- a/drivers/net/pcs/Kconfig
+++ b/drivers/net/pcs/Kconfig
@@ -18,6 +18,13 @@ config PCS_LYNX
 	  This module provides helpers to phylink for managing the Lynx PCS
 	  which is part of the Layerscape and QorIQ Ethernet SERDES.
 
+config PCS_MTK_LYNXI
+	tristate
+	select REGMAP
+	help
+	  This module provides helpers to phylink for managing the LynxI PCS
+	  which is part of MediaTek's SoC and Ethernet switch ICs.
+
 config PCS_RZN1_MIIC
 	tristate "Renesas RZ/N1 MII converter"
 	depends on OF && (ARCH_RZN1 || COMPILE_TEST)
diff --git a/drivers/net/pcs/Makefile b/drivers/net/pcs/Makefile
index 4c780d8f2e984..9b9afd6b1c22d 100644
--- a/drivers/net/pcs/Makefile
+++ b/drivers/net/pcs/Makefile
@@ -5,5 +5,6 @@ pcs_xpcs-$(CONFIG_PCS_XPCS)	:= pcs-xpcs.o pcs-xpcs-nxp.o
 
 obj-$(CONFIG_PCS_XPCS)		+= pcs_xpcs.o
 obj-$(CONFIG_PCS_LYNX)		+= pcs-lynx.o
+obj-$(CONFIG_PCS_MTK_LYNXI)	+= pcs-mtk-lynxi.o
 obj-$(CONFIG_PCS_RZN1_MIIC)	+= pcs-rzn1-miic.o
 obj-$(CONFIG_PCS_ALTERA_TSE)	+= pcs-altera-tse.o
diff --git a/drivers/net/pcs/pcs-mtk-lynxi.c b/drivers/net/pcs/pcs-mtk-lynxi.c
new file mode 100644
index 0000000000000..110fa73060715
--- /dev/null
+++ b/drivers/net/pcs/pcs-mtk-lynxi.c
@@ -0,0 +1,302 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2018-2019 MediaTek Inc.
+/* A library for MediaTek SGMII circuit
+ *
+ * Author: Sean Wang <sean.wang@mediatek.com>
+ * Author: Daniel Golle <daniel@makrotopia.org>
+ *
+ */
+
+#include <linux/mdio.h>
+#include <linux/of.h>
+#include <linux/pcs/pcs-mtk-lynxi.h>
+#include <linux/phylink.h>
+#include <linux/regmap.h>
+
+/* SGMII subsystem config registers */
+/* BMCR (low 16) BMSR (high 16) */
+#define SGMSYS_PCS_CONTROL_1		0x0
+#define SGMII_BMCR			GENMASK(15, 0)
+#define SGMII_BMSR			GENMASK(31, 16)
+
+#define SGMSYS_PCS_DEVICE_ID		0x4
+#define SGMII_LYNXI_DEV_ID		0x4d544950
+
+#define SGMSYS_PCS_ADVERTISE		0x8
+#define SGMII_ADVERTISE			GENMASK(15, 0)
+#define SGMII_LPA			GENMASK(31, 16)
+
+#define SGMSYS_PCS_SCRATCH		0x14
+#define SGMII_DEV_VERSION		GENMASK(31, 16)
+
+/* Register to programmable link timer, the unit in 2 * 8ns */
+#define SGMSYS_PCS_LINK_TIMER		0x18
+#define SGMII_LINK_TIMER_MASK		GENMASK(19, 0)
+
+/* Register to control remote fault */
+#define SGMSYS_SGMII_MODE		0x20
+#define SGMII_IF_MODE_SGMII		BIT(0)
+#define SGMII_SPEED_DUPLEX_AN		BIT(1)
+#define SGMII_SPEED_MASK		GENMASK(3, 2)
+#define SGMII_SPEED_10			FIELD_PREP(SGMII_SPEED_MASK, 0)
+#define SGMII_SPEED_100			FIELD_PREP(SGMII_SPEED_MASK, 1)
+#define SGMII_SPEED_1000		FIELD_PREP(SGMII_SPEED_MASK, 2)
+#define SGMII_DUPLEX_HALF		BIT(4)
+#define SGMII_REMOTE_FAULT_DIS		BIT(8)
+
+/* Register to reset SGMII design */
+#define SGMSYS_RESERVED_0		0x34
+#define SGMII_SW_RESET			BIT(0)
+
+/* Register to set SGMII speed, ANA RG_ Control Signals III */
+#define RG_PHY_SPEED_MASK		(BIT(2) | BIT(3))
+#define SGMII_PHY_SPEED_1_25G		0x0
+#define SGMII_PHY_SPEED_3_125G		BIT(2)
+
+/* Register to power up QPHY */
+#define SGMSYS_QPHY_PWR_STATE_CTRL	0xe8
+#define	SGMII_PHYA_PWD			BIT(4)
+
+/* Register to QPHY wrapper control */
+#define SGMSYS_QPHY_WRAP_CTRL		0xec
+#define SGMII_PN_SWAP_MASK		GENMASK(1, 0)
+#define SGMII_PN_SWAP_TX_RX		(BIT(0) | BIT(1))
+
+/* struct mtk_pcs_lynxi -  This structure holds each sgmii regmap andassociated
+ *                         data
+ * @regmap:                The register map pointing at the range used to setup
+ *                         SGMII modes
+ * @dev:                   Pointer to device owning the PCS
+ * @ana_rgc3:              The offset of register ANA_RGC3 relative to regmap
+ * @interface:             Currently configured interface mode
+ * @pcs:                   Phylink PCS structure
+ * @flags:                 Flags indicating hardware properties
+ */
+struct mtk_pcs_lynxi {
+	struct regmap		*regmap;
+	u32			ana_rgc3;
+	phy_interface_t		interface;
+	struct			phylink_pcs pcs;
+	u32			flags;
+};
+
+static struct mtk_pcs_lynxi *pcs_to_mtk_pcs_lynxi(struct phylink_pcs *pcs)
+{
+	return container_of(pcs, struct mtk_pcs_lynxi, pcs);
+}
+
+static void mtk_pcs_lynxi_get_state(struct phylink_pcs *pcs,
+				    struct phylink_link_state *state)
+{
+	struct mtk_pcs_lynxi *mpcs = pcs_to_mtk_pcs_lynxi(pcs);
+	unsigned int bm, adv;
+
+	/* Read the BMSR and LPA */
+	regmap_read(mpcs->regmap, SGMSYS_PCS_CONTROL_1, &bm);
+	regmap_read(mpcs->regmap, SGMSYS_PCS_ADVERTISE, &adv);
+
+	phylink_mii_c22_pcs_decode_state(state, FIELD_GET(SGMII_BMSR, bm),
+					 FIELD_GET(SGMII_LPA, adv));
+}
+
+static int mtk_pcs_lynxi_config(struct phylink_pcs *pcs, unsigned int mode,
+				phy_interface_t interface,
+				const unsigned long *advertising,
+				bool permit_pause_to_mac)
+{
+	struct mtk_pcs_lynxi *mpcs = pcs_to_mtk_pcs_lynxi(pcs);
+	unsigned int rgc3, sgm_mode, bmcr;
+	int advertise, link_timer;
+	bool mode_changed = false, changed, use_an;
+
+	advertise = phylink_mii_c22_pcs_encode_advertisement(interface,
+							     advertising);
+	if (advertise < 0)
+		return advertise;
+
+	/* Clearing IF_MODE_BIT0 switches the PCS to BASE-X mode, and
+	 * we assume that fixes it's speed at bitrate = line rate (in
+	 * other words, 1000Mbps or 2500Mbps).
+	 */
+	if (interface == PHY_INTERFACE_MODE_SGMII) {
+		sgm_mode = SGMII_IF_MODE_SGMII;
+		if (phylink_autoneg_inband(mode)) {
+			sgm_mode |= SGMII_REMOTE_FAULT_DIS |
+				    SGMII_SPEED_DUPLEX_AN;
+			use_an = true;
+		} else {
+			use_an = false;
+		}
+	} else if (phylink_autoneg_inband(mode)) {
+		/* 1000base-X or 2500base-X autoneg */
+		sgm_mode = SGMII_REMOTE_FAULT_DIS;
+		use_an = linkmode_test_bit(ETHTOOL_LINK_MODE_Autoneg_BIT,
+					   advertising);
+	} else {
+		/* 1000base-X or 2500base-X without autoneg */
+		sgm_mode = 0;
+		use_an = false;
+	}
+
+	if (use_an)
+		bmcr = BMCR_ANENABLE;
+	else
+		bmcr = 0;
+
+	if (mpcs->interface != interface) {
+		link_timer = phylink_get_link_timer_ns(interface);
+		if (link_timer < 0)
+			return link_timer;
+
+		/* PHYA power down */
+		regmap_set_bits(mpcs->regmap, SGMSYS_QPHY_PWR_STATE_CTRL,
+				SGMII_PHYA_PWD);
+
+		/* Reset SGMII PCS state */
+		regmap_set_bits(mpcs->regmap, SGMSYS_RESERVED_0,
+				SGMII_SW_RESET);
+
+		if (mpcs->flags & MTK_SGMII_FLAG_PN_SWAP)
+			regmap_update_bits(mpcs->regmap, SGMSYS_QPHY_WRAP_CTRL,
+					   SGMII_PN_SWAP_MASK,
+					   SGMII_PN_SWAP_TX_RX);
+
+		if (interface == PHY_INTERFACE_MODE_2500BASEX)
+			rgc3 = SGMII_PHY_SPEED_3_125G;
+		else
+			rgc3 = SGMII_PHY_SPEED_1_25G;
+
+		/* Configure the underlying interface speed */
+		regmap_update_bits(mpcs->regmap, mpcs->ana_rgc3,
+				   RG_PHY_SPEED_MASK, rgc3);
+
+		/* Setup the link timer */
+		regmap_write(mpcs->regmap, SGMSYS_PCS_LINK_TIMER,
+			     link_timer / 2 / 8);
+
+		mpcs->interface = interface;
+		mode_changed = true;
+	}
+
+	/* Update the advertisement, noting whether it has changed */
+	regmap_update_bits_check(mpcs->regmap, SGMSYS_PCS_ADVERTISE,
+				 SGMII_ADVERTISE, advertise, &changed);
+
+	/* Update the sgmsys mode register */
+	regmap_update_bits(mpcs->regmap, SGMSYS_SGMII_MODE,
+			   SGMII_REMOTE_FAULT_DIS | SGMII_SPEED_DUPLEX_AN |
+			   SGMII_IF_MODE_SGMII, sgm_mode);
+
+	/* Update the BMCR */
+	regmap_update_bits(mpcs->regmap, SGMSYS_PCS_CONTROL_1,
+			   BMCR_ANENABLE, bmcr);
+
+	/* Release PHYA power down state
+	 * Only removing bit SGMII_PHYA_PWD isn't enough.
+	 * There are cases when the SGMII_PHYA_PWD register contains 0x9 which
+	 * prevents SGMII from working. The SGMII still shows link but no traffic
+	 * can flow. Writing 0x0 to the PHYA_PWD register fix the issue. 0x0 was
+	 * taken from a good working state of the SGMII interface.
+	 * Unknown how much the QPHY needs but it is racy without a sleep.
+	 * Tested on mt7622 & mt7986.
+	 */
+	usleep_range(50, 100);
+	regmap_write(mpcs->regmap, SGMSYS_QPHY_PWR_STATE_CTRL, 0);
+
+	return changed || mode_changed;
+}
+
+static void mtk_pcs_lynxi_restart_an(struct phylink_pcs *pcs)
+{
+	struct mtk_pcs_lynxi *mpcs = pcs_to_mtk_pcs_lynxi(pcs);
+
+	regmap_set_bits(mpcs->regmap, SGMSYS_PCS_CONTROL_1, BMCR_ANRESTART);
+}
+
+static void mtk_pcs_lynxi_link_up(struct phylink_pcs *pcs, unsigned int mode,
+				  phy_interface_t interface, int speed,
+				  int duplex)
+{
+	struct mtk_pcs_lynxi *mpcs = pcs_to_mtk_pcs_lynxi(pcs);
+	unsigned int sgm_mode;
+
+	if (!phylink_autoneg_inband(mode)) {
+		/* Force the speed and duplex setting */
+		if (speed == SPEED_10)
+			sgm_mode = SGMII_SPEED_10;
+		else if (speed == SPEED_100)
+			sgm_mode = SGMII_SPEED_100;
+		else
+			sgm_mode = SGMII_SPEED_1000;
+
+		if (duplex != DUPLEX_FULL)
+			sgm_mode |= SGMII_DUPLEX_HALF;
+
+		regmap_update_bits(mpcs->regmap, SGMSYS_SGMII_MODE,
+				   SGMII_DUPLEX_HALF | SGMII_SPEED_MASK,
+				   sgm_mode);
+	}
+}
+
+static const struct phylink_pcs_ops mtk_pcs_lynxi_ops = {
+	.pcs_get_state = mtk_pcs_lynxi_get_state,
+	.pcs_config = mtk_pcs_lynxi_config,
+	.pcs_an_restart = mtk_pcs_lynxi_restart_an,
+	.pcs_link_up = mtk_pcs_lynxi_link_up,
+};
+
+struct phylink_pcs *mtk_pcs_lynxi_create(struct device *dev,
+					 struct regmap *regmap, u32 ana_rgc3,
+					 u32 flags)
+{
+	struct mtk_pcs_lynxi *mpcs;
+	u32 id, ver;
+	int ret;
+
+	ret = regmap_read(regmap, SGMSYS_PCS_DEVICE_ID, &id);
+	if (ret < 0)
+		return NULL;
+
+	if (id != SGMII_LYNXI_DEV_ID) {
+		dev_err(dev, "unknown PCS device id %08x\n", id);
+		return NULL;
+	}
+
+	ret = regmap_read(regmap, SGMSYS_PCS_SCRATCH, &ver);
+	if (ret < 0)
+		return NULL;
+
+	ver = FIELD_GET(SGMII_DEV_VERSION, ver);
+	if (ver != 0x1) {
+		dev_err(dev, "unknown PCS device version %04x\n", ver);
+		return NULL;
+	}
+
+	dev_dbg(dev, "MediaTek LynxI SGMII PCS (id 0x%08x, ver 0x%04x)\n", id,
+		ver);
+
+	mpcs = kzalloc(sizeof(*mpcs), GFP_KERNEL);
+	if (!mpcs)
+		return NULL;
+
+	mpcs->ana_rgc3 = ana_rgc3;
+	mpcs->regmap = regmap;
+	mpcs->flags = flags;
+	mpcs->pcs.ops = &mtk_pcs_lynxi_ops;
+	mpcs->pcs.poll = true;
+	mpcs->interface = PHY_INTERFACE_MODE_NA;
+
+	return &mpcs->pcs;
+}
+EXPORT_SYMBOL(mtk_pcs_lynxi_create);
+
+void mtk_pcs_lynxi_destroy(struct phylink_pcs *pcs)
+{
+	if (!pcs)
+		return;
+
+	kfree(pcs_to_mtk_pcs_lynxi(pcs));
+}
+EXPORT_SYMBOL(mtk_pcs_lynxi_destroy);
+
+MODULE_LICENSE("GPL");
diff --git a/include/linux/pcs/pcs-mtk-lynxi.h b/include/linux/pcs/pcs-mtk-lynxi.h
new file mode 100644
index 0000000000000..be3b4ab32f4a7
--- /dev/null
+++ b/include/linux/pcs/pcs-mtk-lynxi.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_PCS_MTK_LYNXI_H
+#define __LINUX_PCS_MTK_LYNXI_H
+
+#include <linux/phylink.h>
+#include <linux/regmap.h>
+
+#define MTK_SGMII_FLAG_PN_SWAP BIT(0)
+struct phylink_pcs *mtk_pcs_lynxi_create(struct device *dev,
+					 struct regmap *regmap,
+					 u32 ana_rgc3, u32 flags);
+void mtk_pcs_lynxi_destroy(struct phylink_pcs *pcs);
+#endif
