netdev - [PATCH net-next v2 05/15] net: ethernet: mtk_eth

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Date:   Thu, 22 Apr 2021 22:20:58 -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 v2 05/15] net: ethernet: mtk_eth_soc: reduce MDIO bus access latency

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

usleep_range often ends up sleeping much longer than the 10-20us provided
as a range here. This causes significant latency in mdio bus acceses,
which easily adds multiple seconds to the boot time on MT7621 when polling
DSA slave ports.
Use cond_resched instead of usleep_range, since the MDIO access does not
take much time

Signed-off-by: Felix Fietkau <nbd@....name>
Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@...il.com>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 5cf64de3ddf8..d992d4f1f400 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -86,7 +86,7 @@ static int mtk_mdio_busy_wait(struct mtk_eth *eth)
 			return 0;
 		if (time_after(jiffies, t_start + PHY_IAC_TIMEOUT))
 			break;
-		usleep_range(10, 20);
+		cond_resched();
 	}
 
 	dev_err(eth->dev, "mdio: MDIO timeout\n");
-- 
2.31.1