net: ethernet: mtk_eth_soc: set MDIO bus clock frequency

Set MDIO bus clock frequency and allow setting a custom maximum
frequency from device tree.
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Tested-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mediatek/mtk_eth_soc.c

@@ -765,8 +765,10 @@ static const struct phylink_mac_ops mtk_phylink_ops = {
 
 static int mtk_mdio_init(struct mtk_eth *eth)
 {
+	unsigned int max_clk = 2500000, divider;
 	struct device_node *mii_np;
 	int ret;
+	u32 val;
 
 	mii_np = of_get_child_by_name(eth->dev->of_node, "mdio-bus");
 	if (!mii_np) {
@@ -794,6 +796,25 @@ static int mtk_mdio_init(struct mtk_eth *eth)
 	eth->mii_bus->parent = eth->dev;
 
 	snprintf(eth->mii_bus->id, MII_BUS_ID_SIZE, "%pOFn", mii_np);
+
+	if (!of_property_read_u32(mii_np, "clock-frequency", &val)) {
+		if (val > MDC_MAX_FREQ || val < MDC_MAX_FREQ / MDC_MAX_DIVIDER) {
+			dev_err(eth->dev, "MDIO clock frequency out of range");
+			ret = -EINVAL;
+			goto err_put_node;
+		}
+		max_clk = val;
+	}
+	divider = min_t(unsigned int, DIV_ROUND_UP(MDC_MAX_FREQ, max_clk), 63);
+
+	/* Configure MDC Divider */
+	val = mtk_r32(eth, MTK_PPSC);
+	val &= ~PPSC_MDC_CFG;
+	val |= FIELD_PREP(PPSC_MDC_CFG, divider) | PPSC_MDC_TURBO;
+	mtk_w32(eth, val, MTK_PPSC);
+
+	dev_dbg(eth->dev, "MDC is running on %d Hz\n", MDC_MAX_FREQ / divider);
+
 	ret = of_mdiobus_register(eth->mii_bus, mii_np);
 
 err_put_node:

drivers/net/ethernet/mediatek/mtk_eth_soc.h

@@ -363,6 +363,13 @@
 #define RX_DMA_VTAG_V2		BIT(0)
 #define RX_DMA_L4_VALID_V2	BIT(2)
 
+/* PHY Polling and SMI Master Control registers */
+#define MTK_PPSC		0x10000
+#define PPSC_MDC_CFG		GENMASK(29, 24)
+#define PPSC_MDC_TURBO		BIT(20)
+#define MDC_MAX_FREQ		25000000
+#define MDC_MAX_DIVIDER		63
+
 /* PHY Indirect Access Control registers */
 #define MTK_PHY_IAC		0x10004
 #define PHY_IAC_ACCESS		BIT(31)