linux-kernel - Re: [PATCH net 2/2] net: phy: Check harder for errors in get_phy

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Message-ID: <20200619132659.GB304147@lunn.ch>
Date:   Fri, 19 Jun 2020 15:26:59 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     netdev@...r.kernel.org, Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Dajun Jin <adajunjin@...il.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE" 
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH net 2/2] net: phy: Check harder for errors in get_phy_id()

On Thu, Jun 18, 2020 at 09:47:59PM -0700, Florian Fainelli wrote:
> Commit 02a6efcab675 ("net: phy: allow scanning busses with missing
> phys") added a special condition to return -ENODEV in case -ENODEV or
> -EIO was returned from the first read of the MII_PHYSID1 register.
> 
> In case the MDIO bus data line pull-up is not strong enough, the MDIO
> bus controller will not flag this as a read error. This can happen when
> a pluggable daughter card is not connected and weak internal pull-ups
> are used (since that is the only option, otherwise the pins are
> floating).
> 
> The second read of MII_PHYSID2 will be correctly flagged an error
> though, but now we will return -EIO which will be treated as a hard
> error, thus preventing MDIO bus scanning loops to continue succesfully.
> 
> Apply the same logic to both register reads, thus allowing the scanning
> logic to proceed.

Hi Florian

Maybe extend the kerneldoc for this function to document the return
values and there special meanings?

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

BTW: Did you look at get_phy_c45_ids()? Is it using the correct return
value? Given the current work being done to extend scanning to C45,
maybe it needs reviewing for issues like this.

    Andrew