1 files changed, 42 insertions, 19 deletions

diff --git a/arch/powerpc/sysdev/bestcomm/bestcomm.h b/arch/powerpc/sysdev/bestcomm/bestcomm.h
index c960a8b49655..23a95f80dfdb 100644
--- a/arch/powerpc/sysdev/bestcomm/bestcomm.h
+++ b/arch/powerpc/sysdev/bestcomm/bestcomm.h
@@ -16,8 +16,19 @@
 #ifndef __BESTCOMM_H__
 #define __BESTCOMM_H__
 
-struct bcom_bd; /* defined later on ... */
-
+/**
+ * struct bcom_bd - Structure describing a generic BestComm buffer descriptor
+ * @status: The current status of this buffer. Exact meaning depends on the
+ *          task type
+ * @data: An array of u32 extra data.  Size of array is task dependant.
+ *
+ * Note: Don't dereference a bcom_bd pointer as an array.  The size of the
+ *       bcom_bd is variable.  Use bcom_get_bd() instead.
+ */
+struct bcom_bd {
+        u32     status;
+        u32     data[0];        /* variable payload size */
+};
 
 /* ======================================================================== */
 /* Generic task management                                                   */
@@ -84,17 +95,6 @@ bcom_get_task_irq(struct bcom_task *tsk) {
 /* BD based tasks helpers                                                   */
 /* ======================================================================== */
 
-/**
- * struct bcom_bd - Structure describing a generic BestComm buffer descriptor
- * @status: The current status of this buffer. Exact meaning depends on the
- *          task type
- * @data: An array of u32 whose meaning depends on the task type.
- */
-struct bcom_bd {
-        u32     status;
-        u32     data[1];        /* variable, but at least 1 */
-};
-
 #define BCOM_BD_READY   0x40000000ul
 
 /** _bcom_next_index - Get next input index.
@@ -140,15 +140,31 @@ bcom_queue_full(struct bcom_task *tsk)
 }
 
 /**
+ * bcom_get_bd - Get a BD from the queue
+ * @tsk: The BestComm task structure
+ * index: Index of the BD to fetch
+ */
+static inline struct bcom_bd
+*bcom_get_bd(struct bcom_task *tsk, unsigned int index)
+{
+        /* A cast to (void*) so the address can be incremented by the
+         * real size instead of by sizeof(struct bcom_bd) */
+        return ((void *)tsk->bd) + (index * tsk->bd_size);
+}
+
+/**
  * bcom_buffer_done - Checks if a BestComm 
  * @tsk: The BestComm task structure
  */
 static inline int
 bcom_buffer_done(struct bcom_task *tsk)
 {
+        struct bcom_bd *bd;
         if (bcom_queue_empty(tsk))
                 return 0;
-        return !(tsk->bd[tsk->outdex].status & BCOM_BD_READY);
+
+        bd = bcom_get_bd(tsk, tsk->outdex);
+        return !(bd->status & BCOM_BD_READY);
 }
 
 /**
@@ -160,16 +176,21 @@ bcom_buffer_done(struct bcom_task *tsk)
 static inline struct bcom_bd *
 bcom_prepare_next_buffer(struct bcom_task *tsk)
 {
-        tsk->bd[tsk->index].status = 0; /* cleanup last status */
-        return &tsk->bd[tsk->index];
+        struct bcom_bd *bd;
+
+        bd = bcom_get_bd(tsk, tsk->index);
+        bd->status = 0; /* cleanup last status */
+        return bd;
 }
 
 static inline void
 bcom_submit_next_buffer(struct bcom_task *tsk, void *cookie)
 {
+        struct bcom_bd *bd = bcom_get_bd(tsk, tsk->index);
+
         tsk->cookie[tsk->index] = cookie;
         mb();   /* ensure the bd is really up-to-date */
-        tsk->bd[tsk->index].status |= BCOM_BD_READY;
+        bd->status |= BCOM_BD_READY;
         tsk->index = _bcom_next_index(tsk);
         if (tsk->flags & BCOM_FLAGS_ENABLE_TASK)
                 bcom_enable(tsk);
@@ -179,10 +200,12 @@ static inline void *
 bcom_retrieve_buffer(struct bcom_task *tsk, u32 *p_status, struct bcom_bd **p_bd)
 {
         void *cookie = tsk->cookie[tsk->outdex];
+        struct bcom_bd *bd = bcom_get_bd(tsk, tsk->outdex);
+
         if (p_status)
-                *p_status = tsk->bd[tsk->outdex].status;
+                *p_status = bd->status;
         if (p_bd)
-                *p_bd = &tsk->bd[tsk->outdex];
+                *p_bd = bd;
         tsk->outdex = _bcom_next_outdex(tsk);
         return cookie;
 }