[PATCH] net: phy: realtek: Add rtl8211e rx/tx delays config

[Serge Semin]

There are two chip pins named TXDLY and RXDLY which actually addes
the 2ns delays to TXC and RXC for TXD/RXD latching. Alas it is only
documented info regarding the RGMII timing control configurations
the PHY provides. It turnes out the same settings can be setup
via MDIO registers hidden in the extension pages layout.
Particularly the extension page 0xa4 provides a register 0x1c,
which bits 1 and 2 control the described delays. They are used
to implemet the "rgmii-{id,rxid,txid}" phy-mode.

The hidden RGMII configs register utilization was found in the
rtl8211e U-boot driver:
https://elixir.bootlin.com/u-boot/v2019.01/source/drivers/net/phy/realtek.c#L99

There is also a freebsd discussion regarding this register:
https://reviews.freebsd.org/D13591

It confirms that the register bits field must control the so called
configuration pins described in the table 12-13 of the official PHY
datasheet:
8:6 = PHY Address
5:4 = Auto-Negotiation
3 = Interface Mode Select
2 = RX Delay
1 = TX Delay
0 = SELRGV

Signed-off-by: Serge Semin <fancer.lancer@xxxxxxxxx>
---
 drivers/net/phy/realtek.c | 44 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/drivers/net/phy/realtek.c b/drivers/net/phy/realtek.c
index 10df52ccddfe..8776b94d91ed 100644
--- a/drivers/net/phy/realtek.c
+++ b/drivers/net/phy/realtek.c
@@ -23,11 +23,14 @@
 
 #define RTL821x_INSR				0x13
 
+#define RTL821x_EXT_PAGE_SELECT			0x1e
 #define RTL821x_PAGE_SELECT			0x1f
 
 #define RTL8211F_INSR				0x1d
 
 #define RTL8211F_TX_DELAY			BIT(8)
+#define RTL8211E_TX_DELAY			BIT(1)
+#define RTL8211E_RX_DELAY			BIT(2)
 
 #define RTL8201F_ISR				0x1e
 #define RTL8201F_IER				0x13
@@ -174,6 +177,46 @@ static int rtl8211f_config_init(struct phy_device *phydev)
 	return phy_modify_paged(phydev, 0xd08, 0x11, RTL8211F_TX_DELAY, val);
 }
 
+static int rtl8211e_config_init(struct phy_device *phydev)
+{
+	int ret, oldpage;
+	u16 val = 0;
+
+	ret = genphy_config_init(phydev);
+	if (ret < 0)
+		return ret;
+
+	/* enable TX/RX delay for rgmii-* modes, otherwise disable it */
+	if (phydev->interface == PHY_INTERFACE_MODE_RGMII_ID)
+		val = RTL8211E_TX_DELAY | RTL8211E_RX_DELAY;
+	else if (phydev->interface == PHY_INTERFACE_MODE_RGMII_TXID)
+		val = RTL8211E_TX_DELAY;
+	else if (phydev->interface == PHY_INTERFACE_MODE_RGMII_RXID)
+		val = RTL8211E_RX_DELAY;
+
+	/* According to a sample driver there is a 0x1c config register on
+	 * a 0xa4 extension page (0x7) layout. It can be used to disable/enable
+	 * the RX/TX delays otherwise controlled by hardware strobes. It can
+	 * also be used to customize the whole configuration register:
+	 * 8:6 = PHY Address, 5:4 = Auto-Negotiation, 3 = Interface Mode Select,
+	 * 2 = RX Delay, 1 = TX Delay, 0 = SELRGV (see original PHY datasheet
+	 * for details).
+	 */
+	oldpage = phy_select_page(phydev, 0x7);
+	if (oldpage < 0)
+		goto err_restore_page;
+
+	ret = phy_write(phydev, RTL821x_EXT_PAGE_SELECT, 0xa4);
+	if (!ret)
+		goto err_restore_page;
+
+	ret = phy_modify(phydev, 0x1c, RTL8211E_TX_DELAY | RTL8211E_RX_DELAY,
+			 val);
+
+err_restore_page:
+	return phy_restore_page(phydev, oldpage, ret);
+}
+
 static int rtl8211b_suspend(struct phy_device *phydev)
 {
 	phy_write(phydev, MII_MMD_DATA, BIT(9));
@@ -257,6 +300,7 @@ static struct phy_driver realtek_drvs[] = {
 		PHY_ID_MATCH_EXACT(0x001cc915),
 		.name		= "RTL8211E Gigabit Ethernet",
 		.features	= PHY_GBIT_FEATURES,
+		.config_init	= &rtl8211e_config_init,
 		.ack_interrupt	= &rtl821x_ack_interrupt,
 		.config_intr	= &rtl8211e_config_intr,
 		.suspend	= genphy_suspend,
-- 
2.21.0