asm-generic: add generic versions of common headers

These are all kernel internal interfaces that get copied
around a lot. In most cases, architectures can provide
their own optimized versions, but these generic versions
can work as well.

I have tried to use the most common contents of each
header to allow existing architectures to migrate easily.

Thanks to Remis for suggesting a number of cleanups.

Signed-off-by: Remis Lima Baima <remis.developer@googlemail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

include/asm-generic/scatterlist.h

@@ -0,0 +1,43 @@
+#ifndef __ASM_GENERIC_SCATTERLIST_H
+#define __ASM_GENERIC_SCATTERLIST_H
+
+#include <linux/types.h>
+
+struct scatterlist {
+#ifdef CONFIG_DEBUG_SG
+	unsigned long	sg_magic;
+#endif
+	unsigned long	page_link;
+	unsigned int	offset;
+	unsigned int	length;
+	dma_addr_t	dma_address;
+	unsigned int	dma_length;
+};
+
+/*
+ * These macros should be used after a dma_map_sg call has been done
+ * to get bus addresses of each of the SG entries and their lengths.
+ * You should only work with the number of sg entries pci_map_sg
+ * returns, or alternatively stop on the first sg_dma_len(sg) which
+ * 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
+#define sg_dma_len(sg)		((sg)->dma_length)
+#else
+#define sg_dma_len(sg)		((sg)->length)
+#endif /* 64 bit */
+#endif /* sg_dma_len */
+
+#ifndef ISA_DMA_THRESHOLD
+#define ISA_DMA_THRESHOLD	(~0UL)
+#endif
+
+#define ARCH_HAS_SG_CHAIN
+
+#endif /* __ASM_GENERIC_SCATTERLIST_H */