netdev - [PATCH net-next 11/14] net: ethernet: mtk_eth_soc: only read the full RX descriptor if DMA is done

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Message-Id: <20210422040914.47788-12-ilya.lipnitskiy@gmail.com>
Date:   Wed, 21 Apr 2021 21:09:11 -0700
From:   Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>
To:     Felix Fietkau <nbd@....name>, John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Cc:     Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>
Subject: [PATCH net-next 11/14] net: ethernet: mtk_eth_soc: only read the full RX descriptor if DMA is done

From: Felix Fietkau <nbd@....name>

Uncached memory access is expensive, and there is no need to access all
descriptor words if we can't process them anyway

Signed-off-by: Felix Fietkau <nbd@....name>
Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 01ad10c76d53..5a531bb83348 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -775,13 +775,18 @@ static inline int mtk_max_buf_size(int frag_size)
 	return buf_size;
 }
 
-static inline void mtk_rx_get_desc(struct mtk_rx_dma *rxd,
+static inline bool mtk_rx_get_desc(struct mtk_rx_dma *rxd,
 				   struct mtk_rx_dma *dma_rxd)
 {
-	rxd->rxd1 = READ_ONCE(dma_rxd->rxd1);
 	rxd->rxd2 = READ_ONCE(dma_rxd->rxd2);
+	if (!(rxd->rxd2 & RX_DMA_DONE))
+		return false;
+
+	rxd->rxd1 = READ_ONCE(dma_rxd->rxd1);
 	rxd->rxd3 = READ_ONCE(dma_rxd->rxd3);
 	rxd->rxd4 = READ_ONCE(dma_rxd->rxd4);
+
+	return true;
 }
 
 /* the qdma core needs scratch memory to be setup */
@@ -1253,8 +1258,7 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
 		rxd = &ring->dma[idx];
 		data = ring->data[idx];
 
-		mtk_rx_get_desc(&trxd, rxd);
-		if (!(trxd.rxd2 & RX_DMA_DONE))
+		if (!mtk_rx_get_desc(&trxd, rxd))
 			break;
 
 		/* find out which mac the packet come from. values start at 1 */
-- 
2.31.1