qed: Fix qed_chain_set_prod() for PBL chains with non power of 2 page count

In PBL chains with non power of 2 page count, the producer is not at the
beginning of the chain when index is 0 after a wrap. Therefore, after the
producer index wrap around, page index should be calculated more carefully.
Signed-off-by: Denis Bolotin <dbolotin@marvell.com>
Signed-off-by: Ariel Elior <aelior@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/qed/qed_chain.h

@@ -663,6 +663,37 @@ static inline void *qed_chain_get_last_elem(struct qed_chain *p_chain)
 static inline void qed_chain_set_prod(struct qed_chain *p_chain,
 				      u32 prod_idx, void *p_prod_elem)
 {
+	if (p_chain->mode == QED_CHAIN_MODE_PBL) {
+		u32 cur_prod, page_mask, page_cnt, page_diff;
+
+		cur_prod = is_chain_u16(p_chain) ? p_chain->u.chain16.prod_idx :
+			   p_chain->u.chain32.prod_idx;
+
+		/* Assume that number of elements in a page is power of 2 */
+		page_mask = ~p_chain->elem_per_page_mask;
+
+		/* Use "cur_prod - 1" and "prod_idx - 1" since producer index
+		 * reaches the first element of next page before the page index
+		 * is incremented. See qed_chain_produce().
+		 * Index wrap around is not a problem because the difference
+		 * between current and given producer indices is always
+		 * positive and lower than the chain's capacity.
+		 */
+		page_diff = (((cur_prod - 1) & page_mask) -
+			     ((prod_idx - 1) & page_mask)) /
+			    p_chain->elem_per_page;
+
+		page_cnt = qed_chain_get_page_cnt(p_chain);
+		if (is_chain_u16(p_chain))
+			p_chain->pbl.c.u16.prod_page_idx =
+				(p_chain->pbl.c.u16.prod_page_idx -
+				 page_diff + page_cnt) % page_cnt;
+		else
+			p_chain->pbl.c.u32.prod_page_idx =
+				(p_chain->pbl.c.u32.prod_page_idx -
+				 page_diff + page_cnt) % page_cnt;
+	}
+
 	if (is_chain_u16(p_chain))
 		p_chain->u.chain16.prod_idx = (u16) prod_idx;
 	else