MFC r256637:

  When calculating the number of bounce pages needed, round the maxsize
  up to a multiple of PAGE_SIZE, and add one page because there can always
  be one more boundary crossing than the number of pages in the transfer.

1 files changed, 19 insertions, 10 deletions

diff --git a/sys/arm/arm/busdma_machdep-v6.c b/sys/arm/arm/busdma_machdep-v6.c
index b4f4110..15329ac 100644
--- a/sys/arm/arm/busdma_machdep-v6.c
+++ b/sys/arm/arm/busdma_machdep-v6.c
@@ -425,14 +425,21 @@ bus_dma_tag_create(bus_dma_tag_t parent, bus_size_t alignment,
 	if (_bus_dma_can_bounce(newtag->lowaddr, newtag->highaddr)
 	 || newtag->alignment > 1)
 		newtag->flags |= BUS_DMA_COULD_BOUNCE;
-	else
-		maxsize = 2; /* Need at most 2 bounce pages for unaligned access on cache line boundaries */
 
+	/*
+	 * Any request can auto-bounce due to cacheline alignment, in addition
+	 * to any alignment or boundary specifications in the tag, so if the
+	 * ALLOCNOW flag is set, there's always work to do.
+	 */
 	if ((flags & BUS_DMA_ALLOCNOW) != 0) {
 		struct bounce_zone *bz;
-
-		/* Must bounce */
-
+		/*
+		 * Round size up to a full page, and add one more page because
+		 * there can always be one more boundary crossing than the
+		 * number of pages in a transfer.
+		 */
+		maxsize = roundup2(maxsize, PAGE_SIZE) + PAGE_SIZE;
+		
 		if ((error = alloc_bounce_zone(newtag)) != 0) {
 			free(newtag, M_DEVBUF);
 			return (error);
@@ -518,20 +525,22 @@ static int allocate_bz_and_pages(bus_dma_tag_t dmat, bus_dmamap_t mapp)
 	STAILQ_INIT(&(mapp->bpages));
 
 	/*
-	 * Attempt to add pages to our pool on a per-instance
-	 * basis up to a sane limit.
+	 * Attempt to add pages to our pool on a per-instance basis up to a sane
+	 * limit.  Even if the tag isn't flagged as COULD_BOUNCE due to
+	 * alignment and boundary constraints, it could still auto-bounce due to
+	 * cacheline alignment, which requires at most two bounce pages.
 	 */
 	if (dmat->flags & BUS_DMA_COULD_BOUNCE)
 		maxpages = MAX_BPAGES;
 	else
-		maxpages = 2 * bz->map_count; /* Only need at most 2 pages for buffers unaligned on cache line boundaries */
+		maxpages = 2 * bz->map_count;
 	if ((dmat->flags & BUS_DMA_MIN_ALLOC_COMP) == 0
 	    || (bz->map_count > 0 && bz->total_bpages < maxpages)) {
 		int pages;
 		
-		pages = MAX(atop(dmat->maxsize), 1);
+		pages = atop(roundup2(dmat->maxsize, PAGE_SIZE)) + 1;
 		pages = MIN(maxpages - bz->total_bpages, pages);
-		pages = MAX(pages, 1);
+		pages = MAX(pages, 2);
 		if (alloc_bounce_pages(dmat, pages) < pages)
 			return (ENOMEM);