usb: gadget: Add support for DMA mapping optimization of request buffers

In order to improve performance, this patch enabled mapping of USB request
buffers in advance, before queueing them to the HW. This can be used when
there is a pool or pre-mapped request buffers so we don't need to map it
again every time the request gets queued.

Change-Id: Ic3a6db749343ef1345e0816210517755aee055b3
Signed-off-by: Danny Segal <dsegal@codeaurora.org>
Signed-off-by: Mayank Rana <mrana@codeaurora.org>

2 files changed, 14 insertions, 2 deletions

diff --git a/drivers/usb/gadget/udc/udc-core.c b/drivers/usb/gadget/udc/udc-core.c
index f660afba715d..c148a4fdfe99 100644
--- a/drivers/usb/gadget/udc/udc-core.c
+++ b/drivers/usb/gadget/udc/udc-core.c
@@ -76,7 +76,7 @@ int usb_gadget_map_request(struct usb_gadget *gadget,
 		}
 
 		req->num_mapped_sgs = mapped;
-	} else {
+	} else if (!req->dma_pre_mapped) {
 		req->dma = dma_map_single(dev, req->buf, req->length,
 				is_in ? DMA_TO_DEVICE : DMA_FROM_DEVICE);
 
@@ -101,9 +101,15 @@ void usb_gadget_unmap_request(struct usb_gadget *gadget,
 				is_in ? DMA_TO_DEVICE : DMA_FROM_DEVICE);
 
 		req->num_mapped_sgs = 0;
-	} else {
+	} else if (!req->dma_pre_mapped && req->dma != DMA_ERROR_CODE) {
+		/*
+		 * If the DMA address has not been mapped by a higher layer,
+		 * then unmap it here. Otherwise, the DMA address will be
+		 * unmapped by the upper layer (where the request was queued).
+		 */
 		dma_unmap_single(gadget->dev.parent, req->dma, req->length,
 				is_in ? DMA_TO_DEVICE : DMA_FROM_DEVICE);
+		req->dma = DMA_ERROR_CODE;
 	}
 }
 EXPORT_SYMBOL_GPL(usb_gadget_unmap_request);
diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
index 3f572d5dc16d..ab06d2988505 100644
--- a/include/linux/usb/gadget.h
+++ b/include/linux/usb/gadget.h
@@ -118,6 +118,11 @@ struct gsi_channel_info {
  *     by adding a zero length packet as needed;
  * @short_not_ok: When reading data, makes short packets be
  *     treated as errors (queue stops advancing till cleanup).
+ * @dma_pre_mapped: Tells the USB core driver whether this request should be
+ *	DMA-mapped before it is queued to the USB HW. When set to true, it means
+ *	that the request has already been mapped in advance and therefore the
+ *	USB core driver does NOT need to do DMA-mapping when the request is
+ *	queued to the USB HW.
  * @complete: Function called when request completes, so this request and
  *	its buffer may be re-used.  The function will always be called with
  *	interrupts disabled, and it must not sleep.
@@ -174,6 +179,7 @@ struct usb_request {
 	unsigned		no_interrupt:1;
 	unsigned		zero:1;
 	unsigned		short_not_ok:1;
+	unsigned		dma_pre_mapped:1;
 
 	void			(*complete)(struct usb_ep *ep,
 					struct usb_request *req);