netdev - Re: [PATCH] net: phy: return EPROBE_DEFER if PHY is not accessible

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Message-ID: <3e904a01-7ea8-705c-bf7a-05059729cebf@gmail.com>
Date:   Fri, 17 Mar 2023 19:21:20 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     arturo.buzarra@...i.com
Cc:     netdev@...r.kernel.org, Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Russell King - ARM Linux <linux@...linux.org.uk>
Subject: Re: [PATCH] net: phy: return EPROBE_DEFER if PHY is not accessible

On 17.03.2023 13:16, arturo.buzarra@...i.com wrote:
> From: Arturo Buzarra <arturo.buzarra@...i.com>
> 
> A PHY driver can dynamically determine the devices features, but in some
> circunstances, the PHY is not yet ready and the read capabilities does not fail
> but returns an undefined value, so incorrect capabilities are assumed and the
> initialization process fails. This commit postpones the PHY probe to ensure the
> PHY is accessible.
> 
To complement what has been said by Florian and Andrew:

"under some circumstances" is too vague in general. List potential such
circumstances and best what happened exactly in your case.

When genphy_read_abilities() is called the PHY has been accessed already,
reading the PHY ID. 

So best start with some details about your use case, which MAC, which PHY, etc.

> Signed-off-by: Arturo Buzarra <arturo.buzarra@...i.com>
> ---
>  drivers/net/phy/phy_device.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 1785f1cead97..f8c31e741936 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -2628,10 +2628,14 @@ int genphy_read_abilities(struct phy_device *phydev)
>  			       phydev->supported);
>  
>  	val = phy_read(phydev, MII_BMSR);
>  	if (val < 0)
>  		return val;
> +	if (val == 0x0000 || val == 0xffff) {
> +		phydev_err(phydev, "PHY is not accessible\n");
> +		return -EPROBE_DEFER;
> +	}
>  
>  	linkmode_mod_bit(ETHTOOL_LINK_MODE_Autoneg_BIT, phydev->supported,
>  			 val & BMSR_ANEGCAPABLE);
>  
>  	linkmode_mod_bit(ETHTOOL_LINK_MODE_100baseT_Full_BIT, phydev->supported,