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Date:      Wed, 16 Oct 2013 16:32:35 +0000 (UTC)
From:      Ian Lepore <ian@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r256637 - head/sys/arm/arm
Message-ID:  <201310161632.r9GGWZmC031116@svn.freebsd.org>

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Author: ian
Date: Wed Oct 16 16:32:35 2013
New Revision: 256637
URL: http://svnweb.freebsd.org/changeset/base/256637

Log:
  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.

Modified:
  head/sys/arm/arm/busdma_machdep-v6.c

Modified: head/sys/arm/arm/busdma_machdep-v6.c
==============================================================================
--- head/sys/arm/arm/busdma_machdep-v6.c	Wed Oct 16 16:05:49 2013	(r256636)
+++ head/sys/arm/arm/busdma_machdep-v6.c	Wed Oct 16 16:32:35 2013	(r256637)
@@ -425,14 +425,21 @@ bus_dma_tag_create(bus_dma_tag_t parent,
 	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
 	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);
 		



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