This replaces scatterlist->page_link LSB encodings with SG_CHAIN and
SG_LAST definitions without any functional change. While here also
add macro definitions SG_PAGE_BITS and SG_PAGE_MASK.

Signed-off-by: Anshuman Khandual <khand...@linux.vnet.ibm.com>
---
Changes in V3:
- Changed SG_END as SG_LAST due to a build failure
- Added SG_PAGE_BITS and SG_PAGE_MASK as per Tvrtko
- Used BIT() macro as per Chris

Changes in V2:
- Changed SG_EMARK as SG_END as per Johannes and Tvrtko
- Added 'UL' to the constants as per Bart

 include/linux/scatterlist.h | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 22b2131bcdcd..494b84c7f3c8 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -66,15 +66,20 @@ struct sg_table {
 
 #define SG_MAGIC       0x87654321
 
+#define SG_CHAIN       BIT(0)
+#define SG_LAST                BIT(1)
+#define SG_PAGE_BITS   (SG_CHAIN | SG_LAST)
+#define SG_PAGE_MASK   (~SG_PAGE_BITS)
+
 /*
  * 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)                ((sg)->page_link & 0x01)
-#define sg_is_last(sg)         ((sg)->page_link & 0x02)
+#define sg_is_chain(sg)                ((sg)->page_link & SG_CHAIN)
+#define sg_is_last(sg)         ((sg)->page_link & SG_LAST)
 #define sg_chain_ptr(sg)       \
-       ((struct scatterlist *) ((sg)->page_link & ~0x03))
+       ((struct scatterlist *) ((sg)->page_link & SG_PAGE_MASK))
 
 /**
  * sg_assign_page - Assign a given page to an SG entry
@@ -88,13 +93,13 @@ struct sg_table {
  **/
 static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
 {
-       unsigned long page_link = sg->page_link & 0x3;
+       unsigned long page_link = sg->page_link & SG_PAGE_BITS;
 
        /*
         * In order for the low bit stealing approach to work, pages
         * must be aligned at a 32-bit boundary as a minimum.
         */
-       BUG_ON((unsigned long) page & 0x03);
+       BUG_ON((unsigned long) page & SG_PAGE_BITS);
 #ifdef CONFIG_DEBUG_SG
        BUG_ON(sg->sg_magic != SG_MAGIC);
        BUG_ON(sg_is_chain(sg));
@@ -130,7 +135,7 @@ static inline struct page *sg_page(struct scatterlist *sg)
        BUG_ON(sg->sg_magic != SG_MAGIC);
        BUG_ON(sg_is_chain(sg));
 #endif
-       return (struct page *)((sg)->page_link & ~0x3);
+       return (struct page *)((sg)->page_link & SG_PAGE_MASK);
 }
 
 /**
@@ -178,7 +183,8 @@ static inline void sg_chain(struct scatterlist *prv, 
unsigned int prv_nents,
         * Set lowest bit to indicate a link pointer, and make sure to clear
         * the termination bit if it happens to be set.
         */
-       prv[prv_nents - 1].page_link = ((unsigned long) sgl | 0x01) & ~0x02;
+       prv[prv_nents - 1].page_link = ((unsigned long) sgl | SG_CHAIN)
+                                       & ~SG_LAST;
 }
 
 /**
@@ -198,8 +204,8 @@ static inline void sg_mark_end(struct scatterlist *sg)
        /*
         * Set termination bit, clear potential chain bit
         */
-       sg->page_link |= 0x02;
-       sg->page_link &= ~0x01;
+       sg->page_link |= SG_LAST;
+       sg->page_link &= ~SG_CHAIN;
 }
 
 /**
@@ -215,7 +221,7 @@ static inline void sg_unmark_end(struct scatterlist *sg)
 #ifdef CONFIG_DEBUG_SG
        BUG_ON(sg->sg_magic != SG_MAGIC);
 #endif
-       sg->page_link &= ~0x02;
+       sg->page_link &= ~SG_LAST;
 }
 
 /**
-- 
2.11.0

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