vio: create routines for inc,dec vio dring indexes

Both sunvdc and sunvnet implemented distinct functionality for incrementing
and decrementing dring indexes. Create common functions for use by both
from the sunvnet versions, which were chosen since they will still work
correctly in case a non power of two ring size is used.

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 15 insertions, 0 deletions

diff --git a/arch/sparc/include/asm/vio.h b/arch/sparc/include/asm/vio.h
index fb124feb363b..8174f6cdbbbb 100644
--- a/arch/sparc/include/asm/vio.h
+++ b/arch/sparc/include/asm/vio.h
@@ -300,6 +300,21 @@ static inline u32 vio_dring_avail(struct vio_dring_state *dr,
                 ((dr->prod - dr->cons) & (ring_size - 1)) - 1);
 }
 
+static inline u32 vio_dring_next(struct vio_dring_state *dr, u32 index)
+{
+        if (++index == dr->num_entries)
+                index = 0;
+        return index;
+}
+
+static inline u32 vio_dring_prev(struct vio_dring_state *dr, u32 index)
+{
+        if (index == 0)
+                return dr->num_entries - 1;
+        else
+                return index - 1;
+}
+
 #define VIO_MAX_TYPE_LEN        32
 #define VIO_MAX_COMPAT_LEN      64