4 files changed, 97 insertions, 8 deletions

diff --git a/include/linux/i2o.h b/include/linux/i2o.h
index 9752307d16ba..7da5b98d90e6 100644
--- a/include/linux/i2o.h
+++ b/include/linux/i2o.h
@@ -32,6 +32,7 @@
 #include <linux/workqueue.h>    /* work_struct */
 #include <linux/mempool.h>
 #include <linux/mutex.h>
+#include <linux/scatterlist.h>
 
 #include <asm/io.h>
 #include <asm/semaphore.h>      /* Needed for MUTEX init macros */
@@ -837,7 +838,7 @@ static inline int i2o_dma_map_sg(struct i2o_controller *c,
                 if ((sizeof(dma_addr_t) > 4) && c->pae_support)
                         *mptr++ = cpu_to_le32(i2o_dma_high(sg_dma_address(sg)));
 #endif
-                sg++;
+                sg = sg_next(sg);
         }
         *sg_ptr = mptr;
 
diff --git a/include/linux/ide.h b/include/linux/ide.h
index 234fa3df24f6..30a1931466a6 100644
--- a/include/linux/ide.h
+++ b/include/linux/ide.h
@@ -772,7 +772,7 @@ typedef struct hwif_s {
 
         unsigned int nsect;
         unsigned int nleft;
-        unsigned int cursg;
+        struct scatterlist *cursg;
         unsigned int cursg_ofs;
 
         int             rqsize;         /* max sectors per request */
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 229a9ff9f924..377e6d4d9be3 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -29,7 +29,7 @@
 #include <linux/delay.h>
 #include <linux/interrupt.h>
 #include <linux/dma-mapping.h>
-#include <asm/scatterlist.h>
+#include <linux/scatterlist.h>
 #include <linux/io.h>
 #include <linux/ata.h>
 #include <linux/workqueue.h>
@@ -416,6 +416,7 @@ struct ata_queued_cmd {
         unsigned long           flags;          /* ATA_QCFLAG_xxx */
         unsigned int            tag;
         unsigned int            n_elem;
+        unsigned int            n_iter;
         unsigned int            orig_n_elem;
 
         int                     dma_dir;
@@ -426,7 +427,7 @@ struct ata_queued_cmd {
         unsigned int            nbytes;
         unsigned int            curbytes;
 
-        unsigned int            cursg;
+        struct scatterlist      *cursg;
         unsigned int            cursg_ofs;
 
         struct scatterlist      sgent;
@@ -1043,7 +1044,7 @@ ata_sg_is_last(struct scatterlist *sg, struct ata_queued_cmd *qc)
                 return 1;
         if (qc->pad_len)
                 return 0;
-        if (((sg - qc->__sg) + 1) == qc->n_elem)
+        if (qc->n_iter == qc->n_elem)
                 return 1;
         return 0;
 }
@@ -1051,6 +1052,7 @@ ata_sg_is_last(struct scatterlist *sg, struct ata_queued_cmd *qc)
 static inline struct scatterlist *
 ata_qc_first_sg(struct ata_queued_cmd *qc)
 {
+        qc->n_iter = 0;
         if (qc->n_elem)
                 return qc->__sg;
         if (qc->pad_len)
@@ -1063,8 +1065,8 @@ ata_qc_next_sg(struct scatterlist *sg, struct ata_queued_cmd *qc)
 {
         if (sg == &qc->pad_sgent)
                 return NULL;
-        if (++sg - qc->__sg < qc->n_elem)
-                return sg;
+        if (++qc->n_iter < qc->n_elem)
+                return sg_next(sg);
         if (qc->pad_len)
                 return &qc->pad_sgent;
         return NULL;
@@ -1309,9 +1311,11 @@ static inline void ata_qc_reinit(struct ata_queued_cmd *qc)
         qc->dma_dir = DMA_NONE;
         qc->__sg = NULL;
         qc->flags = 0;
-        qc->cursg = qc->cursg_ofs = 0;
+        qc->cursg = NULL;
+        qc->cursg_ofs = 0;
         qc->nbytes = qc->curbytes = 0;
         qc->n_elem = 0;
+        qc->n_iter = 0;
         qc->err_mask = 0;
         qc->pad_len = 0;
         qc->sect_size = ATA_SECT_SIZE;
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 4efbd9c445f5..2dc7464cce52 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -20,4 +20,88 @@ static inline void sg_init_one(struct scatterlist *sg, const void *buf,
         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_chain_ptr(sg)        \
+        ((struct scatterlist *) ((unsigned long) (sg)->page & ~0x01))
+
+/**
+ * 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.
+ *
+ */
+static inline struct scatterlist *sg_next(struct scatterlist *sg)
+{
+        sg++;
+
+        if (unlikely(sg_is_chain(sg)))
+                sg = sg_chain_ptr(sg);
+
+        return sg;
+}
+
+/*
+ * Loop over each sg element, following the pointer to a new list if necessary
+ */
+#define for_each_sg(sglist, sg, nr, __i)        \
+        for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
+
+/**
+ * sg_last - return the last scatterlist entry in a list
+ * @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.
+ *
+ * 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)
+{
+#ifndef ARCH_HAS_SG_CHAIN
+        struct scatterlist *ret = &sgl[nents - 1];
+#else
+        struct scatterlist *sg, *ret = NULL;
+        int i;
+
+        for_each_sg(sgl, sg, nents, i)
+                ret = sg;
+
+#endif
+        return ret;
+}
+
+/**
+ * sg_chain - Chain two sglists together
+ * @prv:        First scatterlist
+ * @prv_nents:  Number of entries in prv
+ * @sgl:        Second scatterlist
+ *
+ * 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);
+}
+
 #endif /* _LINUX_SCATTERLIST_H */