README: add documentation for CONFIG_USB_ULPI*

Add documentation for CONFIG_USB_ULPI and CONFIG_USB_ULPI_VIEWPORT
configuration options.

Signed-off-by: Igor Grinberg <grinberg@compulab.co.il>

diff --git a/README b/README
index ff72e47..6fe1e0f 100644 (file)
--- a/README
+++ b/README
@@ -1185,6 +1185,14 @@ The following options need to be configured:
                        for your device
                        - CONFIG_USBD_PRODUCTID 0xFFFF
 
+- ULPI Layer Support:
+               The ULPI (UTMI Low Pin (count) Interface) PHYs are supported via
+               the generic ULPI layer. The generic layer accesses the ULPI PHY
+               via the platform viewport, so you need both the genric layer and
+               the viewport enabled. Currently only Chipidea/ARC based
+               viewport is supported.
+               To enable the ULPI layer support, define CONFIG_USB_ULPI and
+               CONFIG_USB_ULPI_VIEWPORT in your board configuration file.
 
 - MMC Support:
                The MMC controller on the Intel PXA is supported. To