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+Passthrough a device described in the Device Tree to a guest
+============================================================
+
+The example will use the secondary network card for the midway server.
+
+1) Mark the device to let Xen know the device will be used for passthrough.
+This is done in the device tree node describing the device by adding the
+property "xen,passthrough". The command to do it in U-Boot is:
+
+ fdt set /soc/ethernet@fff51000 xen,passthrough
+
+2) Create a partial device tree describing the device. The IRQ are mapped
+1:1 to the guest (i.e VIRQ == IRQ). For MMIO, you will have to find a hole
+in the guest memory layout (see xen/include/public/arch-arm.h, note that
+the layout is not stable and can change between versions of Xen).
+
+/dts-v1/;
+
+/ {
+ /* #*cells are here to keep DTC happy */
+ #address-cells = <2>;
+ #size-cells = <2>;
+
+ aliases {
+ net = &mac0;
+ };
+
+ passthrough {
+ compatible = "simple-bus";
+ ranges;
+ #address-cells = <2>;
+ #size-cells = <2>;
+ mac0: ethernet@10000000 {
+ compatible = "calxeda,hb-xgmac";
+ reg = <0 0x10000000 0 0x1000>;
+ interrupts = <0 80 4 0 81 4 0 82 4>;
+ };
+ };
+};
+
+Note:
+ * The interrupt-parent property will be added by the toolstack in the
+ root node;
+ * The following properies are mandatory with the /passthrough node:
+ - compatible: It should always contain "simple-bus"
+ - ranges
+ - #address-cells
+ - #size-cells
+
+3) Compile the partial guest device with dtc (Device Tree Compiler).
+For our purpose, the compiled file will be called guest-midway.dtb and
+placed in /root in DOM0.
+
+3) Add the following options in the guest configuration file:
+
+device_tree = "/root/guest-midway.dtb"
+dtdev = [ "/soc/ethernet@fff51000" ]
+irqs = [ 112, 113, 114 ]
+iomem = [ "0xfff51,1@0x10000" ]
+
+