[usb] Add the concept of a USB bus maximum transfer size

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/bus/usb.c

@@ -1736,11 +1736,12 @@ void free_usb_hub ( struct usb_hub *hub ) {
  *
  * @v dev		Underlying hardware device
  * @v ports		Number of root hub ports
+ * @v mtu		Largest transfer allowed on the bus
  * @v op		Host controller operations
  * @ret bus		USB bus, or NULL on allocation failure
  */
 struct usb_bus * alloc_usb_bus ( struct device *dev, unsigned int ports,
-				 struct usb_host_operations *op ) {
+				 size_t mtu, struct usb_host_operations *op ) {
 	struct usb_bus *bus;
 
 	/* Allocate and initialise structure */
@@ -1749,6 +1750,7 @@ struct usb_bus * alloc_usb_bus ( struct device *dev, unsigned int ports,
 		goto err_alloc_bus;
 	bus->name = dev->name;
 	bus->dev = dev;
+	bus->mtu = mtu;
 	bus->op = op;
 	INIT_LIST_HEAD ( &bus->devices );
 	INIT_LIST_HEAD ( &bus->hubs );

src/drivers/usb/xhci.c

@@ -3117,7 +3117,7 @@ static int xhci_probe ( struct pci_device *pci ) {
 		goto err_reset;
 
 	/* Allocate USB bus */
-	xhci->bus = alloc_usb_bus ( &pci->dev, xhci->ports,
+	xhci->bus = alloc_usb_bus ( &pci->dev, xhci->ports, XHCI_MTU,
 				    &xhci_operations );
 	if ( ! xhci->bus ) {
 		rc = -ENOMEM;

src/drivers/usb/xhci.h

@@ -24,6 +24,9 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
  */
 #define XHCI_MIN_ALIGN 64
 
+/** Maximum transfer size */
+#define XHCI_MTU 65536
+
 /** xHCI PCI BAR */
 #define XHCI_BAR PCI_BASE_ADDRESS_0
 

src/include/ipxe/usb.h

@@ -865,6 +865,9 @@ struct usb_bus {
 	/** Host controller operations set */
 	struct usb_host_operations *op;
 
+	/** Largest transfer allowed on the bus */
+	size_t mtu;
+
 	/** Root hub */
 	struct usb_hub *hub;
 
@@ -1138,7 +1141,8 @@ extern void free_usb_hub ( struct usb_hub *hub );
 
 extern void usb_port_changed ( struct usb_port *port );
 
-extern struct usb_bus * alloc_usb_bus ( struct device *dev, unsigned int ports,
+extern struct usb_bus * alloc_usb_bus ( struct device *dev,
+					unsigned int ports, size_t mtu,
 					struct usb_host_operations *op );
 extern int register_usb_bus ( struct usb_bus *bus );
 extern void unregister_usb_bus ( struct usb_bus *bus );