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

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Message-ID: <YhOLJwOB/wkwei4L@lunn.ch>
Date:   Mon, 21 Feb 2022 13:52:55 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Baruch Siach <baruch@...s.co.il>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        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: Re: [PATCH] net: mdio-ipq4019: add delay after clock enable

On Mon, Feb 21, 2022 at 01:45:57PM +0200, Baruch Siach wrote:
> 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>

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew