sata, highbank: set tx_atten override bits

Some board designs do not drive the SATA transmit lines within the
specification. The ECME can provide override settings, on a per board
basis, to bring the transmit lines within spec. Read those settings
from the DTB and program them in.

At the time of submission, no production hardware requires this patch.

Signed-off-by: Mark Langsdorf <mark.langsdorf@calxeda.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Documentation/devicetree/bindings/ata/sata_highbank.txt

@@ -20,6 +20,9 @@ Optional properties:
 			indicator lights using the indicated GPIOs
 - calxeda,led-order : a u32 array that map port numbers to offsets within the
 			SGPIO bitstream.
+- calxeda,tx-atten  : a u32 array that contains TX attenuation override
+			codes, one per port. The upper 3 bytes are always
+			0 and thus ignored.
 
 Example:
         sata@ffe08000 {
@@ -31,4 +34,5 @@ Example:
 					&combophy0 2 &combophy0 3>;
 		calxeda,sgpio-gpio =<&gpioh 5 1 &gpioh 6 1 &gpioh 7 1>;
 		calxeda,led-order = <4 0 1 2 3>;
+		calxeda,tx-atten = <0xff 22 0xff 0xff 23>;
         };