linux-kernel - Re: [PATCH net-next 4/5] phy: net: introduce phy_promote_to

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Message-ID: <Y8shrgmEoznYsol7@shell.armlinux.org.uk>
Date:   Fri, 20 Jan 2023 23:20:14 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Michael Walle <michael@...le.cc>
Cc:     Yisen Zhuang <yisen.zhuang@...wei.com>,
        Salil Mehta <salil.mehta@...wei.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Marek Behún <kabel@...nel.org>,
        Xu Liang <lxu@...linear.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 4/5] phy: net: introduce phy_promote_to_c45()

On Fri, Jan 20, 2023 at 11:40:10PM +0100, Michael Walle wrote:
> If not explitly asked to be probed as a C45 PHY, on a bus which is
> capable of doing both C22 and C45 transfers, C45 PHYs are first tried to
> be probed as C22 PHYs. To be able to promote the PHY to be a C45 one,
> the driver can call phy_promote_to_c45() in its probe function.
> 
> This was already done in the mxl-gpy driver by the following snippet:
> 
>    if (!phydev->has_c45) {
>            ret = phy_get_c45_ids(phydev);
>            if (ret < 0)
>                    return ret;
>    }
> 
> Move that code into the core by creating a new function
> phy_promote_to_c45(). If a PHY is promoted, C45-over-C22 access is used,
> regardless if the bus supports C45 or not. That is because there might
> be C22 PHYs on the bus which gets confused by C45 accesses.

It is my understanding that C45 PHYs do not have to respond to C22
accesses. So, wouldn't this lead to some C45 PHYs not being detected?

-- 
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