usb: xhci: add Immediate Data Transfer support

Immediate data transfers (IDT) allow the HCD to copy small chunks of
data (up to 8bytes) directly into its output transfer TRBs. This avoids
the somewhat expensive DMA mappings that are performed by default on
most URBs submissions.

In the case an URB was suitable for IDT. The data is directly copied
into the "Data Buffer Pointer" region of the TRB and the IDT flag is
set. Instead of triggering memory accesses the HC will use the data
directly.

The implementation could cover all kind of output endpoints. Yet
Isochronous endpoints are bypassed as I was unable to find one that
matched IDT's constraints. As we try to bypass the default DMA mappings
on URB buffers we'd need to find a Isochronous device with an
urb->transfer_buffer_length <= 8 bytes.

The implementation takes into account that the 8 byte buffers provided
by the URB will never cross a 64KB boundary.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 9215a28dad406a724959f0315a0444525d0edb90..28250319d0b86002938f7f62b738250992deb046 100644 (file)
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -3275,6 +3275,12 @@ 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;
+                       }
                }
 
                /* Only set interrupt on short packet for IN endpoints */
@@ -3414,6 +3420,12 @@ 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,

diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 7fa58c99f12614962a1f852711b699929799f1e5..255f93f741a046a7ad0d5b2a4e36ea52fdd4c67a 100644 (file)
--- 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. If suitable for IDT only one Transfer TRB per TD is allowed.
+ */
+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);
+}
+
 /**
  * xhci_get_endpoint_index - Used for passing endpoint bitmasks between the core and
  * HCDs.  Find the index for an endpoint given its descriptor.  Use the return
@@ -5154,6 +5169,7 @@ static const struct hc_driver xhci_hc_driver = {
        /*
         * managing i/o requests and associated device resources
         */
+       .map_urb_for_dma =      xhci_map_urb_for_dma,
        .urb_enqueue =          xhci_urb_enqueue,
        .urb_dequeue =          xhci_urb_dequeue,
        .alloc_dev =            xhci_alloc_dev,

diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 9334cdee382a67a8b783b13b9c88a2d1dd4c3da3..abbd4813e8a2588f62b756b784f4d68bd746dd2d 100644 (file)
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1303,6 +1303,8 @@ 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 */
+#define TRB_IDT_MAX_SIZE       8
 
 /* Block Event Interrupt */
 #define        TRB_BEI                 (1<<9)
@@ -2149,6 +2151,21 @@ static inline struct xhci_ring *xhci_urb_to_transfer_ring(struct xhci_hcd *xhci,
                                        urb->stream_id);
 }
 
+/*
+ * TODO: As per spec Isochronous IDT transmissions are supported. We bypass
+ * them anyways as we where unable to find a device that matches the
+ * constraints.
+ */
+static inline bool xhci_urb_suitable_for_idt(struct urb *urb)
+{
+       if (!usb_endpoint_xfer_isoc(&urb->ep->desc) && usb_urb_dir_out(urb) &&
+           usb_endpoint_maxp(&urb->ep->desc) >= TRB_IDT_MAX_SIZE &&
+           urb->transfer_buffer_length <= TRB_IDT_MAX_SIZE)
+               return true;
+
+       return false;
+}
+
 static inline char *xhci_slot_state_string(u32 state)
 {
        switch (state) {