Document xHCI port registers

src/hulk/usb/xhci.d

@@ -203,12 +203,54 @@ struct XHCI
 
     /**
      * Located at offset 0x400 from start of Operational Registers.
+     *
+     * There is one set of these registers for each port of the root hub.
      */
     struct PortRegisters
     {
+        /**
+         * Port Status and Control
+         *
+         * 0 Current Connect Status
+         * 1 Port Enabled/Disabled
+         * 2 reserved
+         * 3 Over-current active
+         * 4 Port Reset
+         * 8:5 Port Link State
+         * 9 Port Power
+         * 13:10 Port Speed
+         * 15:14 Port Indicator Control
+         * 16 Port Link State Write Strobe
+         * 17 Connect Status Change
+         * 18 Port Enable/Disable Change
+         * 19 Warm Port Reset Change
+         * 20 Over-current Change
+         * 21 Port Reset Change
+         * 22 Port Link State Change
+         * 23 Port Config Error Change
+         * 24 Cold Attach Status
+         * 25 Wake on Connect Enable
+         * 26 Wake on Disconnect Enable
+         * 27 Wake on Over-current Enable
+         * 29:28 reserved
+         * 30 Device Removable
+         * 31 Warm Port Reset
+         */
         uint portsc;
+
+        /**
+         * Port Power Management Status and Control
+         */
         uint portpmsc;
+
+        /**
+         * Port Link Info
+         */
         uint portli;
+
+        /**
+         * Port Hardware LPM Control (xHCI v1.1+)
+         */
         uint porthlpmc;
     }
     static assert(PortRegisters.sizeof == 0x10u);