linux-kernel - Re: [PATCH net-next] phy: micrel: ksz8041nl: do not use power down mode

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Message-ID: <efb25ac0-a5f6-fc88-ce6d-f93a174c65f1@csgroup.eu>
Date:   Mon, 18 Oct 2021 13:57:25 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Francesco Dolcini <francesco.dolcini@...adex.com>,
        f.fainelli@...il.com, Andrew Lunn <andrew@...n.ch>,
        Sergei Shtylyov <sergei.shtylyov@...il.com>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Stefan Agner <stefan@...er.ch>,
        Marcel Ziswiler <marcel.ziswiler@...adex.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] phy: micrel: ksz8041nl: do not use power down
 mode

+Sergei Shtylyov

Adding Sergei Shtylyov in the discussion, as he submitted the patch for 
the support of KSZ8041RNLI.


Le 18/10/2021 à 13:27, Francesco Dolcini a écrit :
> On Mon, Oct 18, 2021 at 12:46:14PM +0200, Christophe Leroy wrote:
>>
>>
>> Le 18/10/2021 à 12:18, Francesco Dolcini a écrit :
>>> Hello Christophe,
>>>
>>> On Mon, Oct 18, 2021 at 11:53:03AM +0200, Christophe Leroy wrote:
>>>>
>>>>
>>>> Le 18/10/2021 à 11:42, Francesco Dolcini a écrit :
>>>>> From: Stefan Agner <stefan@...er.ch>
>>>>>
>>>>> Some Micrel KSZ8041NL PHY chips exhibit continous RX errors after using
>>>>> the power down mode bit (0.11). If the PHY is taken out of power down
>>>>> mode in a certain temperature range, the PHY enters a weird state which
>>>>> leads to continously reporting RX errors. In that state, the MAC is not
>>>>> able to receive or send any Ethernet frames and the activity LED is
>>>>> constantly blinking. Since Linux is using the suspend callback when the
>>>>> interface is taken down, ending up in that state can easily happen
>>>>> during a normal startup.
>>>>>
>>>>> Micrel confirmed the issue in errata DS80000700A [*], caused by abnormal
>>>>> clock recovery when using power down mode. Even the latest revision (A4,
>>>>> Revision ID 0x1513) seems to suffer that problem, and according to the
>>>>> errata is not going to be fixed.
>>>>>
>>>>> Remove the suspend/resume callback to avoid using the power down mode
>>>>> completely.
>>>>
>>>> As far as I can see in the ERRATA, KSZ8041 RNLI also has the bug.
>>>> Shoudn't you also remove the suspend/resume on that one (which follows in
>>>> ksphy_driver[])
>>>
>>> Yes, I could, however this patch is coming out of a real issue we had with
>>> KSZ8041NL with this specific phy id (and we have such a patch in our linux
>>> branch since years).
>>>
>>> On the other hand the entry for KSZ8041RNLI in the driver is somehow weird,
>>> since the phy id according to the original commit does not even exists on
>>> the datasheet. Would you be confident applying such errata for that phyid
>>> without having a way of testing it?
>>
>>
>> If your patch was to add the suspend/resume capability I would agree with
>> you, but here we are talking about removing it, so what risk are we taking ?
> yes, you are right.
> 
>> In addition, commit 4bd7b5127bd0 ("micrel: add support for KSZ8041RNLI")
>> clearly tells that the only thing it did was to copy KSZ8041NL entry, so for
>> me updating both entries would really make sense.
>>
>> It looks odd to me that you refer in your commit log to an ERRATA that tells
>> you that the bug also exists on the KSZ8041RNLI and you apply it only
>> partly.
> 
> I think I was not clear enough, the entry I changed should already cover
> KSZ8041RNLI, the phyid is supposed to be just the same according to the
> datasheet. This entry for KSZ8041RNLI seems really special with this
> un-documented phyid.
> But I'm just speculating, I do not have access to these hardware.
> 
> Said that if there are no concern from anybody else, to be on the safe/cautious
> side, I can just update also this entry.
> 
> Francesco
>