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From: Zbigniew Bodek <zbb@FreeBSD.org>
Date: Wed, 8 Jul 2015 13:53:00 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r285270 - head/sys/sys
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Author: zbb
Date: Wed Jul  8 13:52:59 2015
New Revision: 285270
URL: https://svnweb.freebsd.org/changeset/base/285270

Log:
  Add memory barrier to bus_dmamap_sync()
  
  On platforms which are fully IO-coherent, the map might be null.
  We need to guarantee that all data is observable after the
  sync operation is called. Add a memory barrier to ensure that on ARM.
  
  Reviewed by:   andrew, kib
  Obtained from: Semihalf
  Sponsored by:  The FreeBSD Foundation
  Differential Revision: https://reviews.freebsd.org/D3012

Modified:
  head/sys/sys/bus_dma.h

Modified: head/sys/sys/bus_dma.h
==============================================================================
--- head/sys/sys/bus_dma.h	Wed Jul  8 13:19:13 2015	(r285269)
+++ head/sys/sys/bus_dma.h	Wed Jul  8 13:52:59 2015	(r285270)
@@ -282,13 +282,25 @@ int bus_dmamem_alloc(bus_dma_tag_t dmat,
 void bus_dmamem_free(bus_dma_tag_t dmat, void *vaddr, bus_dmamap_t map);
 
 /*
- * Perform a synchronization operation on the given map.
+ * Perform a synchronization operation on the given map. If the map
+ * is NULL we have a fully IO-coherent system. On every ARM architecture
+ * there must be a memory barrier placed to ensure that all data
+ * accesses are visible before going any further.
  */
 void _bus_dmamap_sync(bus_dma_tag_t, bus_dmamap_t, bus_dmasync_op_t);
+#if defined(__arm__)
+	#define __BUS_DMAMAP_SYNC_DEFAULT		mb();
+#elif defined(__aarch64__)
+	#define	__BUS_DMAMAP_SYNC_DEFAULT		dmb(sy);
+#else
+	#define	__BUS_DMAMAP_SYNC_DEFAULT		{}
+#endif
 #define bus_dmamap_sync(dmat, dmamap, op) 			\
 	do {							\
 		if ((dmamap) != NULL)				\
 			_bus_dmamap_sync(dmat, dmamap, op);	\
+		else						\
+			__BUS_DMAMAP_SYNC_DEFAULT		\
 	} while (0)
 
 /*