asm-generic: add NEED_SG_DMA_LENGTH to define sg_dma_len()

There are only two ways to define sg_dma_len(); use sg->dma_length or
sg->length.  This patch introduces NEED_SG_DMA_LENGTH that enables
architectures to choose sg->dma_length or sg->length.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/ia64/Kconfig

@@ -56,6 +56,9 @@ config MMU
 config NEED_DMA_MAP_STATE
 	def_bool y
 
+config NEED_SG_DMA_LENGTH
+	def_bool y
+
 config SWIOTLB
        bool
 

arch/sh/Kconfig

@@ -186,6 +186,9 @@ config DMA_NONCOHERENT
 config NEED_DMA_MAP_STATE
 	def_bool DMA_NONCOHERENT
 
+config NEED_SG_DMA_LENGTH
+	def_bool y
+
 source "init/Kconfig"
 
 source "kernel/Kconfig.freezer"

arch/sparc/Kconfig

@@ -133,6 +133,9 @@ config ZONE_DMA
 config NEED_DMA_MAP_STATE
 	def_bool y
 
+config NEED_SG_DMA_LENGTH
+	def_bool y
+
 config GENERIC_ISA_DMA
 	bool
 	default y if SPARC32

arch/sparc/include/asm/scatterlist.h

 #ifndef _SPARC_SCATTERLIST_H
 #define _SPARC_SCATTERLIST_H
 
-#define sg_dma_len(sg)     	((sg)->dma_length)
-
 #define ISA_DMA_THRESHOLD	(~0UL)
 
 #include <asm-generic/scatterlist.h>

arch/x86/Kconfig

@@ -109,6 +109,9 @@ config SBUS
 config NEED_DMA_MAP_STATE
        def_bool (X86_64 || DMAR || DMA_API_DEBUG)
 
+config NEED_SG_DMA_LENGTH
+	def_bool X86_64
+
 config GENERIC_ISA_DMA
 	def_bool y
 

include/asm-generic/scatterlist.h

@@ -11,7 +11,9 @@ struct scatterlist {
 	unsigned int	offset;
 	unsigned int	length;
 	dma_addr_t	dma_address;
+#ifdef CONFIG_NEED_SG_DMA_LENGTH
 	unsigned int	dma_length;
+#endif
 };
 
 /*
@@ -22,17 +24,12 @@ struct scatterlist {
  * is 0.
  */
 #define sg_dma_address(sg)	((sg)->dma_address)
-#ifndef sg_dma_len
-/*
- * Normally, you have an iommu on 64 bit machines, but not on 32 bit
- * machines. Architectures that are differnt should override this.
- */
-#if __BITS_PER_LONG == 64
+
+#ifdef CONFIG_NEED_SG_DMA_LENGTH
 #define sg_dma_len(sg)		((sg)->dma_length)
 #else
 #define sg_dma_len(sg)		((sg)->length)
-#endif /* 64 bit */
-#endif /* sg_dma_len */
+#endif
 
 #define ARCH_HAS_SG_CHAIN