usbcore: Add flag for whether a host controller uses DMA

This patch (as770b) introduces a new field to usb_bus: a flag
indicating whether or not the host controller uses DMA.  This serves
to encapsulate the computation.  It also means we will have only one
spot to update if the DMA API changes.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/core/hcd.c

@@ -1152,7 +1152,7 @@ int usb_hcd_submit_urb (struct urb *urb, gfp_t mem_flags)
 	/* lower level hcd code should use *_dma exclusively,
 	 * unless it uses pio or talks to another transport.
 	 */
-	if (hcd->self.controller->dma_mask) {
+	if (hcd->self.uses_dma) {
 		if (usb_pipecontrol (urb->pipe)
 			&& !(urb->transfer_flags & URB_NO_SETUP_DMA_MAP))
 			urb->setup_dma = dma_map_single (
@@ -1585,8 +1585,9 @@ void usb_hcd_giveback_urb (struct usb_hcd *hcd, struct urb *urb, struct pt_regs
 	at_root_hub = (urb->dev == hcd->self.root_hub);
 	urb_unlink (urb);
 
-	/* lower level hcd code should use *_dma exclusively */
-	if (hcd->self.controller->dma_mask && !at_root_hub) {
+	/* lower level hcd code should use *_dma exclusively if the
+	 * host controller does DMA */
+	if (hcd->self.uses_dma && !at_root_hub) {
 		if (usb_pipecontrol (urb->pipe)
 			&& !(urb->transfer_flags & URB_NO_SETUP_DMA_MAP))
 			dma_unmap_single (hcd->self.controller, urb->setup_dma,
@@ -1710,6 +1711,7 @@ struct usb_hcd *usb_create_hcd (const struct hc_driver *driver,
 	hcd->self.release = &hcd_release;
 	hcd->self.controller = dev;
 	hcd->self.bus_name = bus_name;
+	hcd->self.uses_dma = (dev->dma_mask != NULL);
 
 	init_timer(&hcd->rh_timer);
 	hcd->rh_timer.function = rh_timer_func;

include/linux/usb.h

@@ -269,6 +269,7 @@ struct usb_bus {
 	struct device *controller;	/* host/master side hardware */
 	int busnum;			/* Bus number (in order of reg) */
 	char *bus_name;			/* stable id (PCI slot_name etc) */
+	u8 uses_dma;			/* Does the host controller use DMA? */
 	u8 otg_port;			/* 0, or number of OTG/HNP port */
 	unsigned is_b_host:1;		/* true during some HNP roleswitches */
 	unsigned b_hnp_enable:1;	/* OTG: did A-Host enable HNP? */