[PATCH net-next 03/12] net: bcmgenet: simplify circular pointer arithmetic

Doug Berger
2017-03-14T00:42:19Z

A 2's complement subtraction will always do a borrow, so masking
off the sign bits is the same as conditionally adding (mask+1).

Signed-off-by: Doug Berger <opendmb@gmail.com>
---
drivers/net/ethernet/broadcom/genet/bcmgenet.c | 19 +++++--------------
1 file changed, 5 insertions(+), 14 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
index f92896835d2a..2c008b09c4e3 100644
--- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
+++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
@@ -1,7 +1,7 @@
/*
* Broadcom GENET (Gigabit Ethernet) controller driver
*
- * Copyright (c) 2014 Broadcom Corporation
+ * Copyright (c) 2014-2017 Broadcom
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
@@ -1175,13 +1175,9 @@ static unsigned int __bcmgenet_tx_reclaim(struct net_device *dev,
unsigned int txbds_processed = 0;

/* Compute how many buffers are transmitted since last xmit call */
- c_index = bcmgenet_tdma_ring_readl(priv, ring->index, TDMA_CONS_INDEX);
- c_index &= DMA_C_INDEX_MASK;
-
- if (likely(c_index >= ring->c_index))
- txbds_ready = c_index - ring->c_index;
- else
- txbds_ready = (DMA_C_INDEX_MASK + 1) - ring->c_index + c_index;
+ c_index = bcmgenet_tdma_ring_readl(priv, ring->index, TDMA_CONS_INDEX)
+ & DMA_C_INDEX_MASK;
+ txbds_ready = (c_index - ring->c_index) & DMA_C_INDEX_MASK;

netif_dbg(priv, tx_done, dev,
"%s ring=%d old_c_index=%u c_index=%u txbds_ready=%u\n",
@@ -1611,12 +1607,7 @@ static unsigned int bcmgenet_desc_rx(struct bcmgenet_rx_ring *ring,
}

p_index &= DMA_P_INDEX_MASK;
-
- if (likely(p_index >= ring->c_index))
- rxpkttoprocess = p_index - ring->c_index;
- else
- rxpkttoprocess = (DMA_C_INDEX_MASK + 1) - ring->c_index +
- p_index;
+ rxpkttoprocess = (p_index - ring->c_index) & DMA_C_INDEX_MASK;

netif_dbg(priv, rx_status, dev,
"RDMA: rxpkttoprocess=%d\n", rxpkttoprocess);
--
2.11.1