Change table chaining layout

Change the page member of the scatterlist structure to be an unsigned
long, and encode more stuff in the lower bits:

- Bits 0 and 1 zero: this is a normal sg entry. Next sg entry is located
  at sg + 1.
- Bit 0 set: this is a chain entry, the next real entry is at ->page_link
  with the two low bits masked off.
- Bit 1 set: this is the final entry in the sg entry. sg_next() will return
  NULL when passed such an entry.

It's thus important that sg table users use the proper accessors to get
and set the page member.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

include/asm-alpha/scatterlist.h

@@ -5,7 +5,7 @@
 #include <asm/types.h>
   
 struct scatterlist {
-	struct page *page;
+	unsigned long page_link;
 	unsigned int offset;
 
 	unsigned int length;

include/asm-arm/scatterlist.h

@@ -5,7 +5,7 @@
 #include <asm/types.h>
 
 struct scatterlist {
-	struct page	*page;		/* buffer page			 */
+	unsigned long	page_link;
 	unsigned int	offset;		/* buffer offset		 */
 	dma_addr_t	dma_address;	/* dma address			 */
 	unsigned int	length;		/* length			 */

include/asm-avr32/scatterlist.h

@@ -4,7 +4,7 @@
 #include <asm/types.h>
 
 struct scatterlist {
-    struct page		*page;
+    unsigned long	page_link;
     unsigned int	offset;
     dma_addr_t		dma_address;
     unsigned int	length;

include/asm-blackfin/scatterlist.h

@@ -4,7 +4,7 @@
 #include <linux/mm.h>
 
 struct scatterlist {
-	struct page *page;
+	unsigned long page_link;
 	unsigned int offset;
 	dma_addr_t dma_address;
 	unsigned int length;

include/asm-cris/scatterlist.h

@@ -6,7 +6,7 @@ struct scatterlist {
 	unsigned int length;
 
 	/* The following is i386 highmem junk - not used by us */
-	struct page * page; /* Location for highmem page, if any */
+	unsigned long page_link;
 	unsigned int offset;/* for highmem, page offset */
 
 };

include/asm-frv/scatterlist.h

@@ -22,7 +22,7 @@
  * and that's it. There's no excuse for not highmem enabling YOUR driver. /jens
  */
 struct scatterlist {
-	struct page	*page;		/* Location for highmem page, if any */
+	unsigned long	page_link;
 	unsigned int	offset;		/* for highmem, page offset */
 
 	dma_addr_t	dma_address;

include/asm-h8300/scatterlist.h

@@ -4,7 +4,7 @@
 #include <asm/types.h>
 
 struct scatterlist {
-	struct page	*page;
+	unsigned long	page_link;
 	unsigned int	offset;
 	dma_addr_t	dma_address;
 	unsigned int	length;

include/asm-ia64/scatterlist.h

@@ -9,7 +9,7 @@
 #include <asm/types.h>
 
 struct scatterlist {
-	struct page *page;
+	unsigned long page_link;
 	unsigned int offset;
 	unsigned int length;	/* buffer length */
 

include/asm-m32r/scatterlist.h

@@ -6,7 +6,7 @@
 struct scatterlist {
     char *  address;    /* Location data is to be transferred to, NULL for
                          * highmem page */
-    struct page * page; /* Location for highmem page, if any */
+    unsigned long page_link;
     unsigned int offset;/* for highmem, page offset */
 
     dma_addr_t dma_address;

include/asm-m68k/scatterlist.h

@@ -4,7 +4,7 @@
 #include <linux/types.h>
 
 struct scatterlist {
-	struct page *page;
+	unsigned long page_link;
 	unsigned int offset;
 	unsigned int length;
 

include/asm-m68knommu/scatterlist.h

@@ -5,7 +5,7 @@
 #include <asm/types.h>
 
 struct scatterlist {
-	struct page	*page;
+	unsigned long	page_link;
 	unsigned int	offset;
 	dma_addr_t	dma_address;
 	unsigned int	length;

include/asm-mips/scatterlist.h

@@ -4,7 +4,7 @@
 #include <asm/types.h>
 
 struct scatterlist {
-	struct page *	page;
+	unsigned long	page_link;
 	unsigned int	offset;
 	dma_addr_t	dma_address;
 	unsigned int	length;

include/asm-parisc/scatterlist.h

@@ -5,7 +5,7 @@
 #include <asm/types.h>
 
 struct scatterlist {
-	struct page *page;
+	unsigned long page_link;
 	unsigned int offset;
 
 	unsigned int length;

include/asm-powerpc/scatterlist.h

@@ -14,7 +14,7 @@
 #include <asm/dma.h>
 
 struct scatterlist {
-	struct page *page;
+	unsigned long page_link;
 	unsigned int offset;
 	unsigned int length;
 

include/asm-s390/scatterlist.h

@@ -2,7 +2,7 @@
 #define _ASMS390_SCATTERLIST_H
 
 struct scatterlist {
-    struct page *page;
+    unsigned long page_link;
     unsigned int offset;
     unsigned int length;
 };

include/asm-sh/scatterlist.h

@@ -4,7 +4,7 @@
 #include <asm/types.h>
 
 struct scatterlist {
-    struct page * page; /* Location for highmem page, if any */
+    unsigned long page_link;
     unsigned int offset;/* for highmem, page offset */
     dma_addr_t dma_address;
     unsigned int length;

include/asm-sh64/scatterlist.h

@@ -14,7 +14,7 @@
 #include <asm/types.h>
 
 struct scatterlist {
-    struct page * page; /* Location for highmem page, if any */
+    unsigned long page_link;
     unsigned int offset;/* for highmem, page offset */
     dma_addr_t dma_address;
     unsigned int length;

include/asm-sparc/scatterlist.h

@@ -5,7 +5,7 @@
 #include <linux/types.h>
 
 struct scatterlist {
-	struct page *page;
+	unsigned long page_link;
 	unsigned int offset;
 
 	unsigned int length;

include/asm-sparc64/scatterlist.h

@@ -6,7 +6,7 @@
 #include <asm/types.h>
 
 struct scatterlist {
-	struct page	*page;
+	unsigned long	page_link;
 	unsigned int	offset;
 
 	unsigned int	length;

include/asm-v850/scatterlist.h

@@ -17,7 +17,7 @@
 #include <asm/types.h>
 
 struct scatterlist {
-	struct page	*page;
+	unsigned long	page_link;
 	unsigned	offset;
 	dma_addr_t	dma_address;
 	unsigned	length;

include/asm-x86/dma-mapping_32.h

@@ -45,9 +45,9 @@ dma_map_sg(struct device *dev, struct scatterlist *sglist, int nents,
 	WARN_ON(nents == 0 || sglist[0].length == 0);
 
 	for_each_sg(sglist, sg, nents, i) {
-		BUG_ON(!sg->page);
+		BUG_ON(!sg_page(sg));
 
-		sg->dma_address = page_to_phys(sg->page) + sg->offset;
+		sg->dma_address = sg_phys(sg);
 	}
 
 	flush_write_buffers();

include/asm-x86/scatterlist_32.h

@@ -4,7 +4,7 @@
 #include <asm/types.h>
 
 struct scatterlist {
-    struct page		*page;
+    unsigned long	page_link;
     unsigned int	offset;
     dma_addr_t		dma_address;
     unsigned int	length;

include/asm-x86/scatterlist_64.h

@@ -4,7 +4,7 @@
 #include <asm/types.h>
 
 struct scatterlist {
-    struct page		*page;
+    unsigned long	page_link;
     unsigned int	offset;
     unsigned int	length;
     dma_addr_t		dma_address;

include/asm-xtensa/scatterlist.h

@@ -14,7 +14,7 @@
 #include <asm/types.h>
 
 struct scatterlist {
-	struct page 	*page;
+	unsigned long	page_link;
 	unsigned int	offset;
 	dma_addr_t	dma_address;
 	unsigned int	length;

include/linux/scatterlist.h

@@ -2,9 +2,26 @@
 #define _LINUX_SCATTERLIST_H
 
 #include <asm/scatterlist.h>
-#include <asm/io.h>
 #include <linux/mm.h>
 #include <linux/string.h>
+#include <asm/io.h>
+
+/*
+ * Notes on SG table design.
+ *
+ * Architectures must provide an unsigned long page_link field in the
+ * scatterlist struct. We use that to place the page pointer AND encode
+ * information about the sg table as well. The two lower bits are reserved
+ * for this information.
+ *
+ * If bit 0 is set, then the page_link contains a pointer to the next sg
+ * table list. Otherwise the next entry is at sg + 1.
+ *
+ * If bit 1 is set, then this sg entry is the last element in a list.
+ *
+ * See sg_next().
+ *
+ */
 
 /**
  * sg_set_page - Set sg entry to point at given page
@@ -20,11 +37,20 @@
  **/
 static inline void sg_set_page(struct scatterlist *sg, struct page *page)
 {
-	sg->page = page;
+	unsigned long page_link = sg->page_link & 0x3;
+
+	sg->page_link = page_link | (unsigned long) page;
 }
 
-#define sg_page(sg)	((sg)->page)
+#define sg_page(sg)	((struct page *) ((sg)->page_link & ~0x3))
 
+/**
+ * sg_set_buf - Set sg entry to point at given data
+ * @sg:		 SG entry
+ * @buf:	 Data
+ * @buflen:	 Data length
+ *
+ **/
 static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
 			      unsigned int buflen)
 {
@@ -38,26 +64,27 @@ static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
  * a valid sg entry, or whether it points to the start of a new scatterlist.
  * Those low bits are there for everyone! (thanks mason :-)
  */
-#define sg_is_chain(sg)		((unsigned long) (sg)->page & 0x01)
+#define sg_is_chain(sg)		((sg)->page_link & 0x01)
+#define sg_is_last(sg)		((sg)->page_link & 0x02)
 #define sg_chain_ptr(sg)	\
-	((struct scatterlist *) ((unsigned long) (sg)->page & ~0x01))
+	((struct scatterlist *) ((sg)->page_link & ~0x03))
 
 /**
  * sg_next - return the next scatterlist entry in a list
  * @sg:		The current sg entry
  *
+ * Description:
  *   Usually the next entry will be @sg@ + 1, but if this sg element is part
  *   of a chained scatterlist, it could jump to the start of a new
  *   scatterlist array.
  *
- * Note that the caller must ensure that there are further entries after
- * the current entry, this function will NOT return NULL for an end-of-list.
- *
- */
+ **/
 static inline struct scatterlist *sg_next(struct scatterlist *sg)
 {
-	sg++;
+	if (sg_is_last(sg))
+		return NULL;
 
+	sg++;
 	if (unlikely(sg_is_chain(sg)))
 		sg = sg_chain_ptr(sg);
 
@@ -75,6 +102,7 @@ static inline struct scatterlist *sg_next(struct scatterlist *sg)
  * @sgl:	First entry in the scatterlist
  * @nents:	Number of entries in the scatterlist
  *
+ * Description:
  *   Should only be used casually, it (currently) scan the entire list
  *   to get the last entry.
  *
@@ -82,7 +110,7 @@ static inline struct scatterlist *sg_next(struct scatterlist *sg)
  *   the important bit is that @nents@ denotes the number of entries that
  *   exist from @sgl@.
  *
- */
+ **/
 static inline struct scatterlist *sg_last(struct scatterlist *sgl,
 					  unsigned int nents)
 {
@@ -105,16 +133,17 @@ static inline struct scatterlist *sg_last(struct scatterlist *sgl,
  * @prv_nents:	Number of entries in prv
  * @sgl:	Second scatterlist
  *
+ * Description:
  *   Links @prv@ and @sgl@ together, to form a longer scatterlist.
  *
- */
+ **/
 static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
 			    struct scatterlist *sgl)
 {
 #ifndef ARCH_HAS_SG_CHAIN
 	BUG();
 #endif
-	prv[prv_nents - 1].page = (struct page *) ((unsigned long) sgl | 0x01);
+	prv[prv_nents - 1].page_link = (unsigned long) sgl | 0x01;
 }
 
 /**
@@ -128,13 +157,14 @@ static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
  **/
 static inline void sg_mark_end(struct scatterlist *sgl, unsigned int nents)
 {
+	sgl[nents - 1].page_link = 0x02;
 }
 
 static inline void __sg_mark_end(struct scatterlist *sg)
 {
+	sg->page_link |= 0x02;
 }
 
-
 /**
  * sg_init_one - Initialize a single entry sg list
  * @sg:		 SG entry