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

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Date:   Sat, 21 Jan 2023 00:27:57 +0100
From:   Michael Walle <michael@...le.cc>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
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()

Am 2023-01-21 00:20, schrieb Russell King (Oracle):
> 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?

In that case, the PHY already has to be a C45 PHY, correct? Because
no access to c22 means, it can't be probed as a c22 phy; therefore,
it has the has_c45 set to true. Then phy_promote_to_c45() is a noop and
c45-over-c22 wont be set.

-michael