From 38f58a4cec217297f218d359b2c4cf2ec457d965 Mon Sep 17 00:00:00 2001
From: scottl <scottl@FreeBSD.org>
Date: Tue, 27 May 2014 21:31:11 +0000
Subject: [PATCH] Eliminate the fake contig_dmamap and replace it with a new
 flag, BUS_DMA_KMEM_ALLOC.  They serve the same purpose, but using the flag
 means that the map can be NULL again, which in turn enables significant
 optimizations for the common case of no bouncing.

Obtained from:	Netflix, Inc.
MFC after:	3 days
---
 sys/x86/x86/busdma_bounce.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/sys/x86/x86/busdma_bounce.c b/sys/x86/x86/busdma_bounce.c
index 3e2f0607b3e6..d1c75f8efa08 100644
--- a/sys/x86/x86/busdma_bounce.c
+++ b/sys/x86/x86/busdma_bounce.c
@@ -62,6 +62,7 @@ __FBSDID("$FreeBSD$");
 enum {
 	BUS_DMA_COULD_BOUNCE	= 0x01,
 	BUS_DMA_MIN_ALLOC_COMP	= 0x02,
+	BUS_DMA_KMEM_ALLOC	= 0x04,
 };
 
 struct bounce_zone;
@@ -125,7 +126,7 @@ struct bus_dmamap {
 
 static STAILQ_HEAD(, bus_dmamap) bounce_map_waitinglist;
 static STAILQ_HEAD(, bus_dmamap) bounce_map_callbacklist;
-static struct bus_dmamap nobounce_dmamap, contig_dmamap;
+static struct bus_dmamap nobounce_dmamap;
 
 static void init_bounce_pages(void *dummy);
 static int alloc_bounce_zone(bus_dma_tag_t dmat);
@@ -346,7 +347,7 @@ static int
 bounce_bus_dmamap_destroy(bus_dma_tag_t dmat, bus_dmamap_t map)
 {
 
-	if (map != NULL && map != &nobounce_dmamap && map != &contig_dmamap) {
+	if (map != NULL && map != &nobounce_dmamap) {
 		if (STAILQ_FIRST(&map->bpages) != NULL) {
 			CTR3(KTR_BUSDMA, "%s: tag %p error %d",
 			    __func__, dmat, EBUSY);
@@ -420,13 +421,13 @@ bounce_bus_dmamem_alloc(bus_dma_tag_t dmat, void** vaddr, int flags,
 		*vaddr = (void *)kmem_alloc_attr(kernel_arena,
 		    dmat->common.maxsize, mflags, 0ul, dmat->common.lowaddr,
 		    attr);
-		*mapp = &contig_dmamap;
+		dmat->bounce_flags |= BUS_DMA_KMEM_ALLOC;
 	} else {
 		*vaddr = (void *)kmem_alloc_contig(kernel_arena,
 		    dmat->common.maxsize, mflags, 0ul, dmat->common.lowaddr,
 		    dmat->common.alignment != 0 ? dmat->common.alignment : 1ul,
 		    dmat->common.boundary, attr);
-		*mapp = &contig_dmamap;
+		dmat->bounce_flags |= BUS_DMA_KMEM_ALLOC;
 	}
 	if (*vaddr == NULL) {
 		CTR4(KTR_BUSDMA, "%s: tag %p tag flags 0x%x error %d",
@@ -449,18 +450,18 @@ bounce_bus_dmamem_free(bus_dma_tag_t dmat, void *vaddr, bus_dmamap_t map)
 {
 	/*
 	 * dmamem does not need to be bounced, so the map should be
-	 * NULL if malloc() was used and contig_dmamap if
-	 * kmem_alloc_contig() was used.
+	 * NULL and the BUS_DMA_KMEM_ALLOC flag cleared if malloc()
+	 * was used and set if kmem_alloc_contig() was used.
 	 */
-	if (!(map == NULL || map == &contig_dmamap))
+	if (map != NULL)
 		panic("bus_dmamem_free: Invalid map freed\n");
-	if (map == NULL)
+	if ((dmat->bounce_flags & BUS_DMA_KMEM_ALLOC) == 0)
 		free(vaddr, M_DEVBUF);
 	else
 		kmem_free(kernel_arena, (vm_offset_t)vaddr,
 		    dmat->common.maxsize);
 	CTR3(KTR_BUSDMA, "%s: tag %p flags 0x%x", __func__, dmat,
-	    dmat->common.flags);
+	    dmat->bounce_flags);
 }
 
 static void
@@ -612,7 +613,7 @@ bounce_bus_dmamap_load_phys(bus_dma_tag_t dmat, bus_dmamap_t map,
 	bus_addr_t curaddr;
 	int error;
 
-	if (map == NULL || map == &contig_dmamap)
+	if (map == NULL)
 		map = &nobounce_dmamap;
 
 	if (segs == NULL)
@@ -665,7 +666,7 @@ bounce_bus_dmamap_load_buffer(bus_dma_tag_t dmat, bus_dmamap_t map, void *buf,
 	vm_offset_t vaddr;
 	int error;
 
-	if (map == NULL || map == &contig_dmamap)
+	if (map == NULL)
 		map = &nobounce_dmamap;
 
 	if (segs == NULL)
@@ -976,7 +977,7 @@ add_bounce_page(bus_dma_tag_t dmat, bus_dmamap_t map, vm_offset_t vaddr,
 	struct bounce_page *bpage;
 
 	KASSERT(dmat->bounce_zone != NULL, ("no bounce zone in dma tag"));
-	KASSERT(map != NULL && map != &nobounce_dmamap && map != &contig_dmamap,
+	KASSERT(map != NULL && map != &nobounce_dmamap,
 	    ("add_bounce_page: bad map %p", map));
 
 	bz = dmat->bounce_zone;