netdev - [PATCH] net: mdio-ipq4019: add delay after clock enable

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Message-Id: <01c6b6afb00c02a48fa99542c5b4c6a2c69092b0.1645443957.git.baruch@tkos.co.il>
Date:   Mon, 21 Feb 2022 13:45:57 +0200
From:   Baruch Siach <baruch@...s.co.il>
To:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>
Cc:     Baruch Siach <baruch.siach@...lu.com>,
        Robert Marko <robert.marko@...tura.hr>,
        Luo Jie <luoj@...eaurora.org>,
        Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        netdev@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: [PATCH] net: mdio-ipq4019: add delay after clock enable

From: Baruch Siach <baruch.siach@...lu.com>

Experimentation shows that PHY detect might fail when the code attempts
MDIO bus read immediately after clock enable. Add delay to stabilize the
clock before bus access.

PHY detect failure started to show after commit 7590fc6f80ac ("net:
mdio: Demote probed message to debug print") that removed coincidental
delay between clock enable and bus access.

10ms is meant to match the time it take to send the probed message over
UART at 115200 bps. This might be a far overshoot.

Fixes: 23a890d493e3 ("net: mdio: Add the reset function for IPQ MDIO driver")
Signed-off-by: Baruch Siach <baruch.siach@...lu.com>
---
 drivers/net/mdio/mdio-ipq4019.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/net/mdio/mdio-ipq4019.c b/drivers/net/mdio/mdio-ipq4019.c
index 5f4cd24a0241..4eba5a91075c 100644
--- a/drivers/net/mdio/mdio-ipq4019.c
+++ b/drivers/net/mdio/mdio-ipq4019.c
@@ -200,7 +200,11 @@ static int ipq_mdio_reset(struct mii_bus *bus)
 	if (ret)
 		return ret;
 
-	return clk_prepare_enable(priv->mdio_clk);
+	ret = clk_prepare_enable(priv->mdio_clk);
+	if (ret == 0)
+		mdelay(10);
+
+	return ret;
 }
 
 static int ipq4019_mdio_probe(struct platform_device *pdev)
-- 
2.34.1