net: stmmac: dwmac-meson8b: use picoseconds for the RGMII RX delay

Amlogic Meson G12A, G12B and SM1 SoCs have a more advanced RGMII RX
delay register which allows picoseconds precision. Parse the new
"rx-internal-delay-ps" property or fall back to the value from the old
"amlogic,rx-delay-ns" property.

No upstream DTB uses the old "amlogic,rx-delay-ns" property (yet).
Only include minimalistic logic to fall back to the old property,
without any special validation (for example if the old and new
property are given at the same time).

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

@@ -82,7 +82,7 @@ struct meson8b_dwmac {
 	phy_interface_t			phy_mode;
 	struct clk			*rgmii_tx_clk;
 	u32				tx_delay_ns;
-	u32				rx_delay_ns;
+	u32				rx_delay_ps;
 	struct clk			*timing_adj_clk;
 };
 
@@ -276,7 +276,7 @@ static int meson8b_init_prg_eth(struct meson8b_dwmac *dwmac)
 	tx_dly_config = FIELD_PREP(PRG_ETH0_TXDLY_MASK,
 				   dwmac->tx_delay_ns >> 1);
 
-	if (dwmac->rx_delay_ns == 2)
+	if (dwmac->rx_delay_ps == 2000)
 		rx_dly_config = PRG_ETH0_ADJ_ENABLE | PRG_ETH0_ADJ_SETUP;
 	else
 		rx_dly_config = 0;
@@ -406,14 +406,19 @@ static int meson8b_dwmac_probe(struct platform_device *pdev)
 				 &dwmac->tx_delay_ns))
 		dwmac->tx_delay_ns = 2;
 
-	/* use 0ns as fallback since this is what most boards actually use */
-	if (of_property_read_u32(pdev->dev.of_node, "amlogic,rx-delay-ns",
-				 &dwmac->rx_delay_ns))
-		dwmac->rx_delay_ns = 0;
+	/* RX delay defaults to 0ps since this is what many boards use */
+	if (of_property_read_u32(pdev->dev.of_node, "rx-internal-delay-ps",
+				 &dwmac->rx_delay_ps)) {
+		if (!of_property_read_u32(pdev->dev.of_node,
+					  "amlogic,rx-delay-ns",
+					  &dwmac->rx_delay_ps))
+			/* convert ns to ps */
+			dwmac->rx_delay_ps *= 1000;
+	}
 
-	if (dwmac->rx_delay_ns != 0 && dwmac->rx_delay_ns != 2) {
+	if (dwmac->rx_delay_ps != 0 && dwmac->rx_delay_ps != 2000) {
 		dev_err(&pdev->dev,
-			"The only allowed RX delays values are: 0ns, 2ns");
+			"The only allowed RX delays values are: 0ps, 2000ps");
 		ret = -EINVAL;
 		goto err_remove_config_dt;
 	}