Add exact PHY ID matching and optional 125 MHz CLKOUT configuration
for the Maxio MAE0621A Gigabit Ethernet PHY. Preserve the existing
hardware configuration when the firmware property is absent.

Signed-off-by: Liu Changjie <liucj1228@outlook.com>
---
 drivers/net/phy/Kconfig  |   8 +++
 drivers/net/phy/Makefile |   1 +
 drivers/net/phy/maxio.c  | 103 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 112 insertions(+)
 create mode 100644 drivers/net/phy/maxio.c

diff --git a/drivers/net/phy/Kconfig b/drivers/net/phy/Kconfig
index 099f25dce..32e1a035b 100644
--- a/drivers/net/phy/Kconfig
+++ b/drivers/net/phy/Kconfig
@@ -283,6 +283,14 @@ config MARVELL_88X2222_PHY
 	  Support for the Marvell 88X2222 Dual-port Multi-speed Ethernet
 	  Transceiver.
 
+config MAXIO_PHY
+	tristate "Maxio Ethernet PHYs"
+	help
+	  Support for Maxio Ethernet PHYs. Currently this driver supports the
+	  MAE0621A Gigabit Ethernet PHY. The driver optionally selects a 125 MHz
+	  clock on the CLKOUT pin while preserving the hardware configuration on
+	  boards which do not request it.
+
 config MAXLINEAR_GPHY
 	tristate "Maxlinear Ethernet PHYs"
 	select POLYNOMIAL if HWMON
diff --git a/drivers/net/phy/Makefile b/drivers/net/phy/Makefile
index de660ae94..7fb3626f0 100644
--- a/drivers/net/phy/Makefile
+++ b/drivers/net/phy/Makefile
@@ -70,6 +70,7 @@ obj-$(CONFIG_MARVELL_10G_PHY)	+= marvell10g.o
 obj-$(CONFIG_MARVELL_PHY)	+= marvell.o
 obj-$(CONFIG_MARVELL_88Q2XXX_PHY)	+= marvell-88q2xxx.o
 obj-$(CONFIG_MARVELL_88X2222_PHY)	+= marvell-88x2222.o
+obj-$(CONFIG_MAXIO_PHY)		+= maxio.o
 obj-$(CONFIG_MAXLINEAR_GPHY)	+= mxl-gpy.o
 obj-$(CONFIG_MAXLINEAR_86110_PHY)	+= mxl-86110.o
 obj-y				+= mediatek/
diff --git a/drivers/net/phy/maxio.c b/drivers/net/phy/maxio.c
new file mode 100644
index 000000000..d2cb23895
--- /dev/null
+++ b/drivers/net/phy/maxio.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Driver for Maxio Ethernet PHYs. */
+
+#include <linux/bitops.h>
+#include <linux/module.h>
+#include <linux/phy.h>
+#include <linux/property.h>
+
+#define MAXIO_MAE0621A_PHY_ID		0x7b744412
+
+#define MAXIO_PAGE_SELECT		0x1f
+#define MAXIO_MAE0621A_PHYCR2_PAGE	0xa43
+#define MAXIO_MAE0621A_PHYCR2		0x19
+#define MAXIO_MAE0621A_CLKOUT_125M	BIT(11)
+#define MAXIO_MAE0621A_CLKOUT_ENABLE	BIT(0)
+
+struct maxio_priv {
+	bool clk_out_125m;
+};
+
+static int maxio_read_page(struct phy_device *phydev)
+{
+	return __phy_read(phydev, MAXIO_PAGE_SELECT);
+}
+
+static int maxio_write_page(struct phy_device *phydev, int page)
+{
+	return __phy_write(phydev, MAXIO_PAGE_SELECT, page);
+}
+
+static int maxio_mae0621a_probe(struct phy_device *phydev)
+{
+	struct device *dev = &phydev->mdio.dev;
+	struct maxio_priv *priv;
+	u32 frequency;
+	int ret;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	phydev->priv = priv;
+
+	ret = device_property_read_u32(dev, "maxio,clk-out-frequency-hz",
+				       &frequency);
+	if (ret == -EINVAL)
+		return 0;
+	if (ret)
+		return ret;
+
+	if (frequency != 125000000) {
+		phydev_err(phydev, "invalid CLKOUT frequency %u\n", frequency);
+		return -EINVAL;
+	}
+
+	priv->clk_out_125m = true;
+
+	return 0;
+}
+
+static int maxio_mae0621a_config_init(struct phy_device *phydev)
+{
+	struct maxio_priv *priv = phydev->priv;
+	int ret;
+
+	if (!priv->clk_out_125m)
+		return 0;
+
+	ret = phy_modify_paged_changed(phydev, MAXIO_MAE0621A_PHYCR2_PAGE,
+				       MAXIO_MAE0621A_PHYCR2,
+				       MAXIO_MAE0621A_CLKOUT_ENABLE |
+				       MAXIO_MAE0621A_CLKOUT_125M,
+				       MAXIO_MAE0621A_CLKOUT_ENABLE |
+				       MAXIO_MAE0621A_CLKOUT_125M);
+	if (ret <= 0)
+		return ret;
+
+	return genphy_soft_reset(phydev);
+}
+
+static struct phy_driver maxio_drivers[] = {
+	{
+		PHY_ID_MATCH_EXACT(MAXIO_MAE0621A_PHY_ID),
+		.name		= "Maxio MAE0621A",
+		.probe		= maxio_mae0621a_probe,
+		.config_init	= maxio_mae0621a_config_init,
+		.suspend	= genphy_suspend,
+		.resume		= genphy_resume,
+		.read_page	= maxio_read_page,
+		.write_page	= maxio_write_page,
+	},
+};
+module_phy_driver(maxio_drivers);
+
+static const struct mdio_device_id __maybe_unused maxio_tbl[] = {
+	{ PHY_ID_MATCH_EXACT(MAXIO_MAE0621A_PHY_ID) },
+	{ }
+};
+MODULE_DEVICE_TABLE(mdio, maxio_tbl);
+
+MODULE_AUTHOR("Liu Changjie <liucj1228@outlook.com>");
+MODULE_DESCRIPTION("Maxio Ethernet PHY driver");
+MODULE_LICENSE("GPL");
-- 
2.55.0