openwrt/target/linux/generic/backport-5.10/610-v5.13-47-net-ethernet-mtk_eth_soc-only-read-the-full-RX-descr.patch

From 816ac3e6e67bdd78d86226c6eb53619780750e92 Mon Sep 17 00:00:00 2001
From: Felix Fietkau <nbd@nbd.name>
Date: Thu, 22 Apr 2021 22:21:04 -0700
Subject: [PATCH] net: ethernet: mtk_eth_soc: only read the full RX descriptor
 if DMA is done

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

--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -777,13 +777,18 @@ static inline int mtk_max_buf_size(int f
 	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 */
@@ -1255,8 +1260,7 @@ static int mtk_poll_rx(struct napi_struc
 		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 */