[PATCH] optional ZONE_DMA: introduce CONFIG_ZONE_DMA

This patch simply defines CONFIG_ZONE_DMA for all arches.  We later do special
things with CONFIG_ZONE_DMA after the VM and an arch are prepared to work
without ZONE_DMA.

CONFIG_ZONE_DMA can be defined in two ways depending on how an architecture
handles ISA DMA.

First if CONFIG_GENERIC_ISA_DMA is set by the arch then we know that the arch
needs ZONE_DMA because ISA DMA devices are supported.  We can catch this in
mm/Kconfig and do not need to modify arch code.

Second, arches may use ZONE_DMA in an unknown way.  We set CONFIG_ZONE_DMA for
all arches that do not set CONFIG_GENERIC_ISA_DMA in order to insure backwards
compatibility.  The arches may later undefine ZONE_DMA if their arch code has
been verified to not depend on ZONE_DMA.

Signed-off-by: Christoph Lameter <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: "Luck, Tony" <[email protected]>
Cc: Kyle McMartin <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: James Bottomley <[email protected]>
Cc: Paul Mundt <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

mm/Kconfig

@@ -139,6 +139,10 @@ config SPLIT_PTLOCK_CPUS
 	default "4096" if PARISC && !PA20
 	default "4"
 
+config ZONE_DMA
+	def_bool y
+	depends on GENERIC_ISA_DMA
+
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