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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Baruch Siach <baruch.siach@siklu.com>,
        Andrew Lunn <andrew@lunn.ch>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 5.15 071/139] net: mdio-ipq4019: add delay after clock enable
Date:   Mon, 28 Feb 2022 18:24:05 +0100
Message-Id: <20220228172355.210584515@linuxfoundation.org>
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From: Baruch Siach <baruch.siach@siklu.com>

commit b6ad6261d27708567b309fdb3102b12c42a070cc upstream.

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@siklu.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/mdio/mdio-ipq4019.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- 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
 	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)