dt-bindings: phy: dp83867: provide a workaround for incorrect RX_CTRL pin strap

The data manual for DP83867IR/CR, SNLS484E[1], revised march 2017,
advises that strapping RX_DV/RX_CTRL pin in mode 1 and 2 is not
supported (see note below Table 5 (4-Level Strap Pins)).

It further advises that if a board has this pin strapped in mode 1 and
mode 2, then to ensure proper operation of the PHY, a software workaround
must be implemented.

Since it is not possible to detect in software if RX_DV/RX_CTRL pin is
incorrectly strapped, add a device-tree property for the board to
advertise this and allow corrective action in software.

[1] http://www.ti.com/lit/ds/snls484e/snls484e.pdf

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
[nsekhar@ti.com: rebase to mainline, split documentation into separate patch]
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/ti,dp83867.txt

@@ -18,6 +18,13 @@ Optional property:
 	- ti,max-output-impedance - MAC Interface Impedance control to set
 				    the programmable output impedance to
 				    maximum value (70 ohms).
+	- ti,dp83867-rxctrl-strap-quirk - This denotes the fact that the
+				    board has RX_DV/RX_CTRL pin strapped in
+				    mode 1 or 2. To ensure PHY operation,
+				    there are specific actions that
+				    software needs to take when this pin is
+				    strapped in these modes. See data manual
+				    for details.
 
 Note: ti,min-output-impedance and ti,max-output-impedance are mutually
       exclusive. When both properties are present ti,max-output-impedance