2018-03-20 02:45:19

by Sinan Kaya

Subject: [PATCH v4 13/17] net: cxgb3: Eliminate duplicate barriers on weakly-ordered archs

Code includes wmb() followed by writel(). writel() already has a barrier on
some architectures like arm64.

This ends up CPU observing two barriers back to back before executing the
register write.

Create a new wrapper function with relaxed write operator. Use the new
wrapper when a write is following a wmb().

Signed-off-by: Sinan Kaya <[email protected]>
---
drivers/net/ethernet/chelsio/cxgb3/adapter.h | 7 +++++++
drivers/net/ethernet/chelsio/cxgb3/sge.c | 19 ++++++++++---------
2 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/drivers/net/ethernet/chelsio/cxgb3/adapter.h b/drivers/net/ethernet/chelsio/cxgb3/adapter.h
index 087ff0f..0e21e66 100644
--- a/drivers/net/ethernet/chelsio/cxgb3/adapter.h
+++ b/drivers/net/ethernet/chelsio/cxgb3/adapter.h
@@ -281,6 +281,13 @@ static inline void t3_write_reg(struct adapter *adapter, u32 reg_addr, u32 val)
writel(val, adapter->regs + reg_addr);
}

+static inline void t3_write_reg_relaxed(struct adapter *adapter, u32 reg_addr,
+ u32 val)
+{
+ CH_DBG(adapter, MMIO, "setting register 0x%x to 0x%x\n", reg_addr, val);
+ writel_relaxed(val, adapter->regs + reg_addr);
+}
+
static inline struct port_info *adap2pinfo(struct adapter *adap, int idx)
{
return netdev_priv(adap->port[idx]);
diff --git a/drivers/net/ethernet/chelsio/cxgb3/sge.c b/drivers/net/ethernet/chelsio/cxgb3/sge.c
index e988caa..0baab06 100644
--- a/drivers/net/ethernet/chelsio/cxgb3/sge.c
+++ b/drivers/net/ethernet/chelsio/cxgb3/sge.c
@@ -487,7 +487,8 @@ static inline void ring_fl_db(struct adapter *adap, struct sge_fl *q)
if (q->pend_cred >= q->credits / 4) {
q->pend_cred = 0;
wmb();
- t3_write_reg(adap, A_SG_KDOORBELL, V_EGRCNTX(q->cntxt_id));
+ t3_write_reg_relaxed(adap, A_SG_KDOORBELL,
+ V_EGRCNTX(q->cntxt_id));
}
}

@@ -1058,8 +1059,8 @@ static inline void check_ring_tx_db(struct adapter *adap, struct sge_txq *q)
}
#else
wmb(); /* write descriptors before telling HW */
- t3_write_reg(adap, A_SG_KDOORBELL,
- F_SELEGRCNTX | V_EGRCNTX(q->cntxt_id));
+ t3_write_reg_relaxed(adap, A_SG_KDOORBELL,
+ F_SELEGRCNTX | V_EGRCNTX(q->cntxt_id));
#endif
}

@@ -1510,8 +1511,8 @@ static int ctrl_xmit(struct adapter *adap, struct sge_txq *q,
}
spin_unlock(&q->lock);
wmb();
- t3_write_reg(adap, A_SG_KDOORBELL,
- F_SELEGRCNTX | V_EGRCNTX(q->cntxt_id));
+ t3_write_reg_relaxed(adap, A_SG_KDOORBELL,
+ F_SELEGRCNTX | V_EGRCNTX(q->cntxt_id));
return NET_XMIT_SUCCESS;
}

@@ -1554,8 +1555,8 @@ static void restart_ctrlq(unsigned long data)

spin_unlock(&q->lock);
wmb();
- t3_write_reg(qs->adap, A_SG_KDOORBELL,
- F_SELEGRCNTX | V_EGRCNTX(q->cntxt_id));
+ t3_write_reg_relaxed(qs->adap, A_SG_KDOORBELL,
+ F_SELEGRCNTX | V_EGRCNTX(q->cntxt_id));
}

/*
@@ -1793,8 +1794,8 @@ again: reclaim_completed_tx(adap, q, TX_RECLAIM_CHUNK);
#endif
wmb();
if (likely(written))
- t3_write_reg(adap, A_SG_KDOORBELL,
- F_SELEGRCNTX | V_EGRCNTX(q->cntxt_id));
+ t3_write_reg_relaxed(adap, A_SG_KDOORBELL,
+ F_SELEGRCNTX | V_EGRCNTX(q->cntxt_id));
}

/**
--
2.7.4