usb: phy: mxs: Add DT bindings to configure TX settings

The TX settings can be calibrated for particular hardware.  The
phy is reset by Linux, so this cannot be handled by the bootloader.

The TRM mentions that the maximum resistance should be used for the
DN/DP calibration in order to pass USB certification.

The values for the TX registers are poorly described in the TRM.
The meanings of the register values were taken from another
NXP-provided document:
https://community.nxp.com/message/566147#comment-566912

Acked-by: Peter Chen <peter.chen@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jaret Cantu <jaret.cantu@timesys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/phy/mxs-usb-phy.txt b/Documentation/devicetree/bindings/phy/mxs-usb-phy.txt
index 379b84a567cc..1d25b04cd05e 100644
--- a/Documentation/devicetree/bindings/phy/mxs-usb-phy.txt
+++ b/Documentation/devicetree/bindings/phy/mxs-usb-phy.txt
@@ -12,6 +12,16 @@ Required properties:
 - interrupts: Should contain phy interrupt
 - fsl,anatop: phandle for anatop register, it is only for imx6 SoC series
 
+Optional properties:
+- fsl,tx-cal-45-dn-ohms: Integer [30-55]. Resistance (in ohms) of switchable
+  high-speed trimming resistor connected in parallel with the 45 ohm resistor
+  that terminates the DN output signal. Default: 45
+- fsl,tx-cal-45-dp-ohms: Integer [30-55]. Resistance (in ohms) of switchable
+  high-speed trimming resistor connected in parallel with the 45 ohm resistor
+  that terminates the DP output signal. Default: 45
+- fsl,tx-d-cal: Integer [79-119]. Current trimming value (as a percentage) of
+  the 17.78mA TX reference current. Default: 100
+
 Example:
 usbphy1: usbphy@020c9000 {
 	compatible = "fsl,imx6q-usbphy", "fsl,imx23-usbphy";