[RFC,v2] usb: xhci: add Immediate Data Transfer support

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 40fa25c4d041..a4efbe62a1a3 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c

@@ -3272,8 +3272,15 @@ int xhci_queue_bulk_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
 			field |= TRB_IOC;
 			more_trbs_coming = false;
 			td->last_trb = ring->enqueue;
+
+			if (xhci_urb_suitable_for_idt(urb)) {
+				memcpy(&send_addr, urb->transfer_buffer,
+				       trb_buff_len);
+				field |= TRB_IDT;
+			}
 		}
 
+

@@ -3411,6 +3418,12 @@ int xhci_queue_ctrl_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
 	if (urb->transfer_buffer_length > 0) {
 		u32 length_field, remainder;
 
+		if (xhci_urb_suitable_for_idt(urb)) {
+			memcpy(&urb->transfer_dma, urb->transfer_buffer,
+			       urb->transfer_buffer_length);
+			field |= TRB_IDT;
+		}
+
 		remainder = xhci_td_remainder(xhci, 0,
 				urb->transfer_buffer_length,
 				urb->transfer_buffer_length,

@@ -3420,6 +3433,7 @@ int xhci_queue_ctrl_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
 				TRB_INTR_TARGET(0);
 		if (setup->bRequestType & USB_DIR_IN)
 			field |= TRB_DIR_IN;
+

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 005e65922608..dec62f7f5dc8 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c

@@ -1238,6 +1238,21 @@ EXPORT_SYMBOL_GPL(xhci_resume);
 
 /*-------------------------------------------------------------------------*/
 
+/*
+ * Bypass the DMA mapping if URB is suitable for Immediate Transfer (IDT),
+ * we'll copy the actual data into the TRB address register. This is limited to
+ * transfers up to 8 bytes on output endpoints of any kind with wMaxPacketSize
+ * >= 8 bytes.
+ */
+static int xhci_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
+				gfp_t mem_flags)
+{
+	if (xhci_urb_suitable_for_idt(urb))
+		return 0;
+
+	return usb_hcd_map_urb_for_dma(hcd, urb, mem_flags);
+}

diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 652dc36e3012..9d77b0901ab7 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h

@@ -1295,6 +1295,8 @@ enum xhci_setup_dev {
 #define TRB_IOC			(1<<5)
 /* The buffer pointer contains immediate data */
 #define TRB_IDT			(1<<6)
+/* TDs smaller than this might use IDT */