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

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Message-ID: <91659f09-44e9-2382-f9ac-e9ac32a85e4b@gmail.com>
Date:   Fri, 19 Jun 2020 11:42:12 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org, Heiner Kallweit <hkallweit1@...il.com>,
        "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 6/19/2020 6:30 AM, Russell King - ARM Linux admin wrote:
> On Fri, Jun 19, 2020 at 03:26:59PM +0200, Andrew Lunn wrote:
>> 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?
> 
> You mean like the patch I sent yesterday?
> 
>> 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.
> 
> And the updates I sent for this yesterday? ;)

When Russell's patches land, they will address this correctly and
because I did not want to introduce any conflicts, this is not addressed
by this two patch series.
-- 
Florian