net: stmmac: dwmac-meson8b: add support for the RGMII RX delay on G12A

Amlogic Meson G12A (and newer: G12B, SM1) SoCs have a more advanced RX
delay logic. Instead of fine-tuning the delay in the nanoseconds range
it now allows tuning in 200 picosecond steps. This support comes with
new bits in the PRG_ETH1[19:16] register.

Add support for validating the RGMII RX delay as well as configuring the
register accordingly on these platforms.
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/stmicro/stmmac/dwmac-meson8b.c

@@ -68,10 +68,21 @@
  */
 #define PRG_ETH0_ADJ_SKEW		GENMASK(24, 20)
 
+#define PRG_ETH1			0x4
+
+/* Defined for adding a delay to the input RX_CLK for better timing.
+ * Each step is 200ps. These bits are used with external RGMII PHYs
+ * because RGMII RX only has the small window. cfg_rxclk_dly can
+ * adjust the window between RX_CLK and RX_DATA and improve the stability
+ * of "rx data valid".
+ */
+#define PRG_ETH1_CFG_RXCLK_DLY		GENMASK(19, 16)
+
 struct meson8b_dwmac;
 
 struct meson8b_dwmac_data {
 	int (*set_phy_mode)(struct meson8b_dwmac *dwmac);
+	bool has_prg_eth1_rgmii_rx_delay;
 };
 
 struct meson8b_dwmac {
@@ -270,30 +281,35 @@ static int meson8b_devm_clk_prepare_enable(struct meson8b_dwmac *dwmac,
 
 static int meson8b_init_rgmii_delays(struct meson8b_dwmac *dwmac)
 {
-	u32 tx_dly_config, rx_dly_config, delay_config;
+	u32 tx_dly_config, rx_adj_config, cfg_rxclk_dly, delay_config;
 	int ret;
 
+	rx_adj_config = 0;
+	cfg_rxclk_dly = 0;
 	tx_dly_config = FIELD_PREP(PRG_ETH0_TXDLY_MASK,
 				   dwmac->tx_delay_ns >> 1);
 
-	if (dwmac->rx_delay_ps == 2000)
-		rx_dly_config = PRG_ETH0_ADJ_ENABLE | PRG_ETH0_ADJ_SETUP;
-	else
-		rx_dly_config = 0;
+	if (dwmac->data->has_prg_eth1_rgmii_rx_delay)
+		cfg_rxclk_dly = FIELD_PREP(PRG_ETH1_CFG_RXCLK_DLY,
+					   dwmac->rx_delay_ps / 200);
+	else if (dwmac->rx_delay_ps == 2000)
+		rx_adj_config = PRG_ETH0_ADJ_ENABLE | PRG_ETH0_ADJ_SETUP;
 
 	switch (dwmac->phy_mode) {
 	case PHY_INTERFACE_MODE_RGMII:
-		delay_config = tx_dly_config | rx_dly_config;
+		delay_config = tx_dly_config | rx_adj_config;
 		break;
 	case PHY_INTERFACE_MODE_RGMII_RXID:
 		delay_config = tx_dly_config;
+		cfg_rxclk_dly = 0;
 		break;
 	case PHY_INTERFACE_MODE_RGMII_TXID:
-		delay_config = rx_dly_config;
+		delay_config = rx_adj_config;
 		break;
 	case PHY_INTERFACE_MODE_RGMII_ID:
 	case PHY_INTERFACE_MODE_RMII:
 		delay_config = 0;
+		cfg_rxclk_dly = 0;
 		break;
 	default:
 		dev_err(dwmac->dev, "unsupported phy-mode %s\n",
@@ -323,6 +339,9 @@ static int meson8b_init_rgmii_delays(struct meson8b_dwmac *dwmac)
 				PRG_ETH0_ADJ_DELAY | PRG_ETH0_ADJ_SKEW,
 				delay_config);
 
+	meson8b_dwmac_mask_bits(dwmac, PRG_ETH1, PRG_ETH1_CFG_RXCLK_DLY,
+				cfg_rxclk_dly);
+
 	return 0;
 }
 
@@ -423,11 +442,20 @@ static int meson8b_dwmac_probe(struct platform_device *pdev)
 			dwmac->rx_delay_ps *= 1000;
 	}
 
-	if (dwmac->rx_delay_ps != 0 && dwmac->rx_delay_ps != 2000) {
-		dev_err(&pdev->dev,
-			"The only allowed RX delays values are: 0ps, 2000ps");
-		ret = -EINVAL;
-		goto err_remove_config_dt;
+	if (dwmac->data->has_prg_eth1_rgmii_rx_delay) {
+		if (dwmac->rx_delay_ps != 0 && dwmac->rx_delay_ps != 2000) {
+			dev_err(dwmac->dev,
+				"The only allowed RGMII RX delays values are: 0ps, 2000ps");
+			ret = -EINVAL;
+			goto err_remove_config_dt;
+		}
+	} else {
+		if (dwmac->rx_delay_ps > 3000 || dwmac->rx_delay_ps % 200) {
+			dev_err(dwmac->dev,
+				"The RGMII RX delay range is 0..3000ps in 200ps steps");
+			ret = -EINVAL;
+			goto err_remove_config_dt;
+		}
 	}
 
 	dwmac->timing_adj_clk = devm_clk_get_optional(dwmac->dev,
@@ -469,10 +497,17 @@ static int meson8b_dwmac_probe(struct platform_device *pdev)
 
 static const struct meson8b_dwmac_data meson8b_dwmac_data = {
 	.set_phy_mode = meson8b_set_phy_mode,
+	.has_prg_eth1_rgmii_rx_delay = false,
 };
 
 static const struct meson8b_dwmac_data meson_axg_dwmac_data = {
 	.set_phy_mode = meson_axg_set_phy_mode,
+	.has_prg_eth1_rgmii_rx_delay = false,
+};
+
+static const struct meson8b_dwmac_data meson_g12a_dwmac_data = {
+	.set_phy_mode = meson_axg_set_phy_mode,
+	.has_prg_eth1_rgmii_rx_delay = true,
 };
 
 static const struct of_device_id meson8b_dwmac_match[] = {
@@ -494,7 +529,7 @@ static const struct of_device_id meson8b_dwmac_match[] = {
 	},
 	{
 		.compatible = "amlogic,meson-g12a-dwmac",
-		.data = &meson_axg_dwmac_data,
+		.data = &meson_g12a_dwmac_data,
 	},
 	{ }
 };