1 files changed, 175 insertions, 27 deletions

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 2dc7464cce52..42daf5e15265 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -4,47 +4,95 @@
 #include <asm/scatterlist.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().
+ *
+ */
+
+#define SG_MAGIC        0x87654321
+
+/**
+ * sg_set_page - Set sg entry to point at given page
+ * @sg:          SG entry
+ * @page:        The page
+ *
+ * Description:
+ *   Use this function to set an sg entry pointing at a page, never assign
+ *   the page directly. We encode sg table information in the lower bits
+ *   of the page pointer. See sg_page() for looking up the page belonging
+ *   to an sg entry.
+ *
+ **/
+static inline void sg_set_page(struct scatterlist *sg, struct page *page)
+{
+        unsigned long page_link = sg->page_link & 0x3;
+
+#ifdef CONFIG_DEBUG_SG
+        BUG_ON(sg->sg_magic != SG_MAGIC);
+#endif
+        sg->page_link = page_link | (unsigned long) 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)
 {
-        sg->page = virt_to_page(buf);
+        sg_set_page(sg, virt_to_page(buf));
         sg->offset = offset_in_page(buf);
         sg->length = buflen;
 }
 
-static inline void sg_init_one(struct scatterlist *sg, const void *buf,
-                               unsigned int buflen)
-{
-        memset(sg, 0, sizeof(*sg));
-        sg_set_buf(sg, buf, buflen);
-}
-
 /*
  * We overload the LSB of the page pointer to indicate whether it's
  * 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
  *
- * 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.
+ * 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.
  *
- */
+ **/
 static inline struct scatterlist *sg_next(struct scatterlist *sg)
 {
-        sg++;
+#ifdef CONFIG_DEBUG_SG
+        BUG_ON(sg->sg_magic != SG_MAGIC);
+#endif
+        if (sg_is_last(sg))
+                return NULL;
 
+        sg++;
         if (unlikely(sg_is_chain(sg)))
                 sg = sg_chain_ptr(sg);
 
@@ -62,14 +110,15 @@ static inline struct scatterlist *sg_next(struct scatterlist *sg)
  * @sgl:        First entry in the scatterlist
  * @nents:      Number of entries in the scatterlist
  *
- * Should only be used casually, it (currently) scan the entire list
- * to get the last entry.
+ * Description:
+ *   Should only be used casually, it (currently) scan the entire list
+ *   to get the last entry.
  *
- * Note that the @sgl@ pointer passed in need not be the first one,
- * the important bit is that @nents@ denotes the number of entries that
- * exist from @sgl@.
+ *   Note that the @sgl@ pointer passed in need not be the first one,
+ *   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)
 {
@@ -83,6 +132,10 @@ static inline struct scatterlist *sg_last(struct scatterlist *sgl,
                 ret = sg;
 
 #endif
+#ifdef CONFIG_DEBUG_SG
+        BUG_ON(sgl[0].sg_magic != SG_MAGIC);
+        BUG_ON(!sg_is_last(ret));
+#endif
         return ret;
 }
 
@@ -92,16 +145,111 @@ static inline struct scatterlist *sg_last(struct scatterlist *sgl,
  * @prv_nents:  Number of entries in prv
  * @sgl:        Second scatterlist
  *
- * Links @prv@ and @sgl@ together, to form a longer 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;
+}
+
+/**
+ * sg_mark_end - Mark the end of the scatterlist
+ * @sgl:        Scatterlist
+ * @nents:      Number of entries in sgl
+ *
+ * Description:
+ *   Marks the last entry as the termination point for sg_next()
+ *
+ **/
+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
+ * @buf:         Virtual address for IO
+ * @buflen:      IO length
+ *
+ * Notes:
+ *   This should not be used on a single entry that is part of a larger
+ *   table. Use sg_init_table() for that.
+ *
+ **/
+static inline void sg_init_one(struct scatterlist *sg, const void *buf,
+                               unsigned int buflen)
+{
+        memset(sg, 0, sizeof(*sg));
+#ifdef CONFIG_DEBUG_SG
+        sg->sg_magic = SG_MAGIC;
+#endif
+        sg_mark_end(sg, 1);
+        sg_set_buf(sg, buf, buflen);
+}
+
+/**
+ * sg_init_table - Initialize SG table
+ * @sgl:           The SG table
+ * @nents:         Number of entries in table
+ *
+ * Notes:
+ *   If this is part of a chained sg table, sg_mark_end() should be
+ *   used only on the last table part.
+ *
+ **/
+static inline void sg_init_table(struct scatterlist *sgl, unsigned int nents)
+{
+        memset(sgl, 0, sizeof(*sgl) * nents);
+        sg_mark_end(sgl, nents);
+#ifdef CONFIG_DEBUG_SG
+        {
+                int i;
+                for (i = 0; i < nents; i++)
+                        sgl[i].sg_magic = SG_MAGIC;
+        }
+#endif
+}
+
+/**
+ * sg_phys - Return physical address of an sg entry
+ * @sg:      SG entry
+ *
+ * Description:
+ *   This calls page_to_phys() on the page in this sg entry, and adds the
+ *   sg offset. The caller must know that it is legal to call page_to_phys()
+ *   on the sg page.
+ *
+ **/
+static inline unsigned long sg_phys(struct scatterlist *sg)
+{
+        return page_to_phys(sg_page(sg)) + sg->offset;
+}
+
+/**
+ * sg_virt - Return virtual address of an sg entry
+ * @sg:      SG entry
+ *
+ * Description:
+ *   This calls page_address() on the page in this sg entry, and adds the
+ *   sg offset. The caller must know that the sg page has a valid virtual
+ *   mapping.
+ *
+ **/
+static inline void *sg_virt(struct scatterlist *sg)
+{
+        return page_address(sg_page(sg)) + sg->offset;
 }
 
 #endif /* _LINUX_SCATTERLIST_H */