[PATCH 4/5] net: phy: dp83867: Disable tx/rx delay when not configured

[Trent Piepho]

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.

Cc: Andrew Lunn <andrew@xxxxxxx>
Cc: Florian Fainelli <f.fainelli@xxxxxxxxx>
Cc: Heiner Kallweit <hkallweit1@xxxxxxxxx>
Signed-off-by: Trent Piepho <tpiepho@xxxxxxxxxx>
---
 drivers/net/phy/dp83867.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/phy/dp83867.c b/drivers/net/phy/dp83867.c
index 420729cd6025..a46cc9427fb3 100644
--- a/drivers/net/phy/dp83867.c
+++ b/drivers/net/phy/dp83867.c
@@ -256,10 +256,16 @@ 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);
 
-- 
2.14.5