dt-bindings: phy: tegra-xusb-padctl: Add nvidia,usb3-port-fake entry

Quoted 8 lines · Thierry Reding

Quoted 7 lines · Nagarjuna Kristam

Add binding details regarding nvidia,usb3-port-fake

Signed-off-by Nagarjuna Kristam <[email protected]>

---
 Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt | 3 +++
 1 file changed, 3 insertions(+)

Quoted 16 lines

Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt Optional properties: · line 163

Quoted 11 lines

Documentation/devicetree/bindings/phy/nvidia,tegra124-xusb-padctl.txt +3 -0

index 3742c15..21a5541 100644
@@ -158,6 +158,9 @@ Optional properties:
   is internal. In the absence of this property the port is considered to be
   external.
 - vbus-supply: phandle to a regulator supplying the VBUS voltage.
+- nvidia,usb3-port-fake: A integer property whose presense informs that a
+  fake USB3 port needs to be mapped for corresponding USB2 port. This entry
+  is applicable only for Tegra210 based platforms which has USB2 only ports.

You don't provide a rationale fo why this fake USB3 port needs to be specified. Doesn't the OTG port work without the fake USB3 port? Why does it need to be specified and which one should be used as fake?

Yes, on Tegra210 based platforms, USB2 only device/OTG ports don't work

Quoted 4 lines

You mention elsewhere that an unused USB3 port is used on Jetson TX1, but what if there are no unused ports on a platform? Can we use any USB3 port for this purpose?

If we dont have any unused port, we cannot get device mode working on USB2 only port. We cannot use any USB3 port, we need to use an un-used USB3 port, so that we can fake that corresponding USB2 only port as USB2 and USB3 port.