netdev - Re: [PATCH] dp83640: Ensure against premature access to PHY registers after reset

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Message-ID: <20180406141410.GI17495@lunn.ch>
Date:   Fri, 6 Apr 2018 16:14:10 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Esben Haabendal <esben.haabendal@...il.com>
Cc:     netdev@...r.kernel.org, Esben Haabendal <eha@...f.com>,
        Richard Cochran <richardcochran@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dp83640: Ensure against premature access to PHY
 registers after reset

On Fri, Apr 06, 2018 at 04:05:40PM +0200, Esben Haabendal wrote:
> From: Esben Haabendal <eha@...f.com>
> 
> Signed-off-by: Esben Haabendal <eha@...f.com>
> ---
>  drivers/net/phy/dp83640.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/drivers/net/phy/dp83640.c b/drivers/net/phy/dp83640.c
> index 654f42d00092..48403170096a 100644
> --- a/drivers/net/phy/dp83640.c
> +++ b/drivers/net/phy/dp83640.c
> @@ -1207,6 +1207,22 @@ static void dp83640_remove(struct phy_device *phydev)
>  	kfree(dp83640);
>  }
>  
> +static int dp83640_soft_reset(struct phy_device *phydev)
> +{
> +	int ret;
> +
> +	ret = genphy_soft_reset(phydev);
> +	if (ret < 0)
> +		return ret;
> +
> +	/* From DP83640 datasheet: "Software driver code must wait 3 us
> +	 * following a software reset before allowing further serial MII
> +	 * operations with the DP83640." */
> +	udelay(3);

Hi Esben

The accuracy of udelay() is not guaranteed. So you probably want to be
a bit pessimistic, and use 10.

  Andrew