net: phy: dp83867: Rework delay rgmii delay handling

The code was assuming the reset default of the delay control register
was to have delay disabled.  This is what the datasheet shows as the
register's initial value.  However, that's not actually true: the
default is controlled by the PHY's pin strapping.

If the interface mode is selected as RX or TX delay only, insure the
other direction's delay is disabled.

If the interface mode is just "rgmii", with neither TX or RX internal
delay, one might expect that the driver should disable both delays.  But
this is not what the driver does.  It leaves the setting at the PHY's
strapping's default.  And that default, for no pins with strapping
resistors, is to have delay enabled and 2.00 ns.

Rather than change this behavior, I've kept it the same and documented
it.  No delay will most likely not work and will break ethernet on any
board using "rgmii" mode.  If the board is strapped to have a delay and
is configured to use "rgmii" mode a warning is generated that "rgmii-id"
should have been used.

Also validate the delay values and fail if they are not in range.

Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Trent Piepho <tpiepho@impinj.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/dp83867.c

@@ -28,6 +28,7 @@
 #define DP83867_CFG4            0x0031
 #define DP83867_RGMIICTL	0x0032
 #define DP83867_STRAP_STS1	0x006E
+#define DP83867_STRAP_STS2	0x006f
 #define DP83867_RGMIIDCTL	0x0086
 #define DP83867_IO_MUX_CFG	0x0170
 
@@ -55,13 +56,23 @@
 /* STRAP_STS1 bits */
 #define DP83867_STRAP_STS1_RESERVED		BIT(11)
 
+/* STRAP_STS2 bits */
+#define DP83867_STRAP_STS2_CLK_SKEW_TX_MASK	GENMASK(6, 4)
+#define DP83867_STRAP_STS2_CLK_SKEW_TX_SHIFT	4
+#define DP83867_STRAP_STS2_CLK_SKEW_RX_MASK	GENMASK(2, 0)
+#define DP83867_STRAP_STS2_CLK_SKEW_RX_SHIFT	0
+#define DP83867_STRAP_STS2_CLK_SKEW_NONE	BIT(2)
+
 /* PHY CTRL bits */
 #define DP83867_PHYCR_FIFO_DEPTH_SHIFT		14
 #define DP83867_PHYCR_FIFO_DEPTH_MASK		(3 << 14)
 #define DP83867_PHYCR_RESERVED_MASK		BIT(11)
 
 /* RGMIIDCTL bits */
+#define DP83867_RGMII_TX_CLK_DELAY_MAX		0xf
 #define DP83867_RGMII_TX_CLK_DELAY_SHIFT	4
+#define DP83867_RGMII_RX_CLK_DELAY_MAX		0xf
+#define DP83867_RGMII_RX_CLK_DELAY_SHIFT	0
 
 /* IO_MUX_CFG bits */
 #define DP83867_IO_MUX_CFG_IO_IMPEDANCE_CTRL	0x1f
@@ -178,19 +189,56 @@ static int dp83867_of_init(struct phy_device *phydev)
 	dp83867->rxctrl_strap_quirk = of_property_read_bool(of_node,
 					"ti,dp83867-rxctrl-strap-quirk");
 
+	/* Existing behavior was to use default pin strapping delay in rgmii
+	 * mode, but rgmii should have meant no delay.  Warn existing users.
+	 */
+	if (phydev->interface == PHY_INTERFACE_MODE_RGMII) {
+		const u16 val = phy_read_mmd(phydev, DP83867_DEVADDR, DP83867_STRAP_STS2);
+		const u16 txskew = (val & DP83867_STRAP_STS2_CLK_SKEW_TX_MASK) >>
+				   DP83867_STRAP_STS2_CLK_SKEW_TX_SHIFT;
+		const u16 rxskew = (val & DP83867_STRAP_STS2_CLK_SKEW_RX_MASK) >>
+				   DP83867_STRAP_STS2_CLK_SKEW_RX_SHIFT;
+
+		if (txskew != DP83867_STRAP_STS2_CLK_SKEW_NONE ||
+		    rxskew != DP83867_STRAP_STS2_CLK_SKEW_NONE)
+			phydev_warn(phydev,
+				    "PHY has delays via pin strapping, but phy-mode = 'rgmii'\n"
+				    "Should be 'rgmii-id' to use internal delays\n");
+	}
+
+	/* RX delay *must* be specified if internal delay of RX is used. */
+	if (phydev->interface == PHY_INTERFACE_MODE_RGMII_ID ||
+	    phydev->interface == PHY_INTERFACE_MODE_RGMII_RXID) {
 		ret = of_property_read_u32(of_node, "ti,rx-internal-delay",
 					   &dp83867->rx_id_delay);
-	if (ret &&
-	    (phydev->interface == PHY_INTERFACE_MODE_RGMII_ID ||
-	     phydev->interface == PHY_INTERFACE_MODE_RGMII_RXID))
+		if (ret) {
+			phydev_err(phydev, "ti,rx-internal-delay must be specified\n");
 			return ret;
+		}
+		if (dp83867->rx_id_delay > DP83867_RGMII_RX_CLK_DELAY_MAX) {
+			phydev_err(phydev,
+				   "ti,rx-internal-delay value of %u out of range\n",
+				   dp83867->rx_id_delay);
+			return -EINVAL;
+		}
+	}
 
+	/* TX delay *must* be specified if internal delay of RX is used. */
+	if (phydev->interface == PHY_INTERFACE_MODE_RGMII_ID ||
+	    phydev->interface == PHY_INTERFACE_MODE_RGMII_TXID) {
 		ret = of_property_read_u32(of_node, "ti,tx-internal-delay",
 					   &dp83867->tx_id_delay);
-	if (ret &&
-	    (phydev->interface == PHY_INTERFACE_MODE_RGMII_ID ||
-	     phydev->interface == PHY_INTERFACE_MODE_RGMII_TXID))
+		if (ret) {
+			phydev_err(phydev, "ti,tx-internal-delay must be specified\n");
 			return ret;
+		}
+		if (dp83867->tx_id_delay > DP83867_RGMII_TX_CLK_DELAY_MAX) {
+			phydev_err(phydev,
+				   "ti,tx-internal-delay value of %u out of range\n",
+				   dp83867->tx_id_delay);
+			return -EINVAL;
+		}
+	}
 
 	if (of_property_read_bool(of_node, "enet-phy-lane-swap"))
 		dp83867->port_mirroring = DP83867_PORT_MIRROING_EN;
@@ -259,10 +307,16 @@ static int dp83867_config_init(struct phy_device *phydev)
 			return ret;
 	}
 
+	/* If rgmii mode with no internal delay is selected, we do NOT use
+	 * aligned mode as one might expect.  Instead we use the PHY's default
+	 * based on pin strapping.  And the "mode 0" default is to *use*
+	 * internal delay with a value of 7 (2.00 ns).
+	 */
 	if ((phydev->interface >= PHY_INTERFACE_MODE_RGMII_ID) &&
 	    (phydev->interface <= PHY_INTERFACE_MODE_RGMII_RXID)) {
 		val = phy_read_mmd(phydev, DP83867_DEVADDR, DP83867_RGMIICTL);
 
+		val &= ~(DP83867_RGMII_TX_CLK_DELAY_EN | DP83867_RGMII_RX_CLK_DELAY_EN);
 		if (phydev->interface == PHY_INTERFACE_MODE_RGMII_ID)
 			val |= (DP83867_RGMII_TX_CLK_DELAY_EN | DP83867_RGMII_RX_CLK_DELAY_EN);