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From:   Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>
To:     Felix Fietkau <nbd@nbd.name>, John Crispin <john@phrozen.org>,
        Sean Wang <sean.wang@mediatek.com>,
        Mark Lee <Mark-MC.Lee@mediatek.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org
Cc:     Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>
Subject: [PATCH net-next 05/14] net: ethernet: mtk_eth_soc: reduce MDIO bus access latency
Date:   Wed, 21 Apr 2021 21:09:05 -0700
Message-Id: <20210422040914.47788-6-ilya.lipnitskiy@gmail.com>
In-Reply-To: <20210422040914.47788-1-ilya.lipnitskiy@gmail.com>
References: <20210422040914.47788-1-ilya.lipnitskiy@gmail.com>
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From: Felix Fietkau <nbd@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 udelay via readx_poll_timeout_atomic, since the MDIO access does not
take much time

Signed-off-by: Felix Fietkau <nbd@nbd.name>
[Ilya: use readx_poll_timeout_atomic instead of cond_resched]
Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 18 ++++++++----------
 drivers/net/ethernet/mediatek/mtk_eth_soc.h |  2 +-
 2 files changed, 9 insertions(+), 11 deletions(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 5cf64de3ddf8..a3958e99a29f 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -79,18 +79,16 @@ static u32 mtk_m32(struct mtk_eth *eth, u32 mask, u32 set, unsigned reg)
 
 static int mtk_mdio_busy_wait(struct mtk_eth *eth)
 {
-	unsigned long t_start = jiffies;
+	int ret;
+	u32 val;
 
-	while (1) {
-		if (!(mtk_r32(eth, MTK_PHY_IAC) & PHY_IAC_ACCESS))
-			return 0;
-		if (time_after(jiffies, t_start + PHY_IAC_TIMEOUT))
-			break;
-		usleep_range(10, 20);
-	}
+	ret = readx_poll_timeout_atomic(__raw_readl, eth->base + MTK_PHY_IAC,
+					val, !(val & PHY_IAC_ACCESS),
+					5, PHY_IAC_TIMEOUT_US);
+	if (ret)
+		dev_err(eth->dev, "mdio: MDIO timeout\n");
 
-	dev_err(eth->dev, "mdio: MDIO timeout\n");
-	return -1;
+	return ret;
 }
 
 static u32 _mtk_mdio_write(struct mtk_eth *eth, u32 phy_addr,
diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.h b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
index 875e67b41561..989342a7ae4a 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.h
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
@@ -327,7 +327,7 @@
 #define PHY_IAC_START		BIT(16)
 #define PHY_IAC_ADDR_SHIFT	20
 #define PHY_IAC_REG_SHIFT	25
-#define PHY_IAC_TIMEOUT		HZ
+#define PHY_IAC_TIMEOUT_US	1000000
 
 #define MTK_MAC_MISC		0x1000c
 #define MTK_MUX_TO_ESW		BIT(0)
-- 
2.31.1