From 8b1ce3297a22ec73faf71ca052131cca877bffe1 Mon Sep 17 00:00:00 2001
From: Hans Petter Selasky <hselasky@FreeBSD.org>
Date: Mon, 2 Feb 2015 11:32:15 +0000
Subject: [PATCH] Optimise allocation of USB DMA structures. By default don't
 double map allocations if only one element should be allocated per page
 cache. Make one allocation per element compile time configurable. Fix a
 comment while at it.

Suggested by:	ian @
MFC after:	1 week
---
 sys/conf/options           |  1 +
 sys/dev/usb/usb_transfer.c | 31 +++++++++++++++++++++++++++----
 2 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/sys/conf/options b/sys/conf/options
index a8802af7c2ed..c23f8f05fe08 100644
--- a/sys/conf/options
+++ b/sys/conf/options
@@ -651,6 +651,7 @@ USB_HOST_ALIGN		opt_usb.h
 USB_REQ_DEBUG		opt_usb.h
 USB_TEMPLATE		opt_usb.h
 USB_VERBOSE		opt_usb.h
+USB_DMA_SINGLE_ALLOC	opt_usb.h
 USB_EHCI_BIG_ENDIAN_DESC	opt_usb.h
 U3G_DEBUG		opt_u3g.h
 UKBD_DFLT_KEYMAP	opt_ukbd.h
diff --git a/sys/dev/usb/usb_transfer.c b/sys/dev/usb/usb_transfer.c
index 0f02fc860e6d..56507905e14e 100644
--- a/sys/dev/usb/usb_transfer.c
+++ b/sys/dev/usb/usb_transfer.c
@@ -237,7 +237,11 @@ usbd_transfer_setup_sub_malloc(struct usb_setup_params *parm,
 		n_obj = 1;
 	} else {
 		/* compute number of objects per page */
+#ifdef USB_DMA_SINGLE_ALLOC
+		n_obj = 1;
+#else
 		n_obj = (USB_PAGE_SIZE / size);
+#endif
 		/*
 		 * Compute number of DMA chunks, rounded up
 		 * to nearest one:
@@ -273,15 +277,33 @@ usbd_transfer_setup_sub_malloc(struct usb_setup_params *parm,
 		    &parm->curr_xfer->xroot->dma_parent_tag;
 	}
 
-	if (ppc) {
-		*ppc = parm->xfer_page_cache_ptr;
+	if (ppc != NULL) {
+		if (n_obj != 1)
+			*ppc = parm->xfer_page_cache_ptr;
+		else
+			*ppc = parm->dma_page_cache_ptr;
 	}
 	r = count;			/* set remainder count */
 	z = n_obj * size;		/* set allocation size */
 	pc = parm->xfer_page_cache_ptr;
 	pg = parm->dma_page_ptr;
 
-	for (x = 0; x != n_dma_pc; x++) {
+	if (n_obj == 1) {
+	    /*
+	     * Avoid mapping memory twice if only a single object
+	     * should be allocated per page cache:
+	     */
+	    for (x = 0; x != n_dma_pc; x++) {
+		if (usb_pc_alloc_mem(parm->dma_page_cache_ptr,
+		    pg, z, align)) {
+			return (1);	/* failure */
+		}
+		/* Make room for one DMA page cache and "n_dma_pg" pages */
+		parm->dma_page_cache_ptr++;
+		pg += n_dma_pg;
+	    }
+	} else {
+	    for (x = 0; x != n_dma_pc; x++) {
 
 		if (r < n_obj) {
 			/* compute last remainder */
@@ -294,7 +316,7 @@ usbd_transfer_setup_sub_malloc(struct usb_setup_params *parm,
 		}
 		/* Set beginning of current buffer */
 		buf = parm->dma_page_cache_ptr->buffer;
-		/* Make room for one DMA page cache and one page */
+		/* Make room for one DMA page cache and "n_dma_pg" pages */
 		parm->dma_page_cache_ptr++;
 		pg += n_dma_pg;
 
@@ -314,6 +336,7 @@ usbd_transfer_setup_sub_malloc(struct usb_setup_params *parm,
 			}
 			mtx_unlock(pc->tag_parent->mtx);
 		}
+	    }
 	}
 
 	parm->xfer_page_cache_ptr = pc;