svn commit: r269136 - head/sys/arm/arm

[Ian Lepore]

Author: ian
Date: Sat Jul 26 18:19:43 2014
New Revision: 269136
URL: http://svnweb.freebsd.org/changeset/base/269136

Log:
  Pull in the armv4 "fast out" code for checking whether busdma can bounce
  due to an excluded region of physical memory.

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	Sat Jul 26 18:14:16 2014	(r269135)
+++ head/sys/arm/arm/busdma_machdep-v6.c	Sat Jul 26 18:19:43 2014	(r269136)
@@ -229,10 +229,26 @@ busdma_init(void *dummy)
  */
 SYSINIT(busdma, SI_SUB_KMEM, SI_ORDER_FOURTH, busdma_init, NULL);
 
+/*
+ * This routine checks the exclusion zone constraints from a tag against the
+ * physical RAM available on the machine.  If a tag specifies an exclusion zone
+ * but there's no RAM in that zone, then we avoid allocating resources to bounce
+ * a request, and we can use any memory allocator (as opposed to needing
+ * kmem_alloc_contig() just because it can allocate pages in an address range).
+ *
+ * Most tags have BUS_SPACE_MAXADDR or BUS_SPACE_MAXADDR_32BIT (they are the
+ * same value on 32-bit architectures) as their lowaddr constraint, and we can't
+ * possibly have RAM at an address higher than the highest address we can
+ * express, so we take a fast out.
+ */
 static __inline int
 _bus_dma_can_bounce(vm_offset_t lowaddr, vm_offset_t highaddr)
 {
 	int i;
+
+	if (lowaddr >= BUS_SPACE_MAXADDR)
+		return (0);
+
 	for (i = 0; phys_avail[i] && phys_avail[i + 1]; i += 2) {
 		if ((lowaddr >= phys_avail[i] && lowaddr <= phys_avail[i + 1])
 		    || (lowaddr < phys_avail[i] &&