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

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Date:   Mon, 18 Oct 2021 19:16:21 +0200
From:   Francesco Dolcini <francesco.dolcini@...adex.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Francesco Dolcini <francesco.dolcini@...adex.com>,
        f.fainelli@...il.com, Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        christophe.leroy@...roup.eu, 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

Hello Jakub,

On Mon, Oct 18, 2021 at 09:52:49AM -0700, Jakub Kicinski wrote:
> On Mon, 18 Oct 2021 11:42:58 +0200 Francesco Dolcini wrote:
> > 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.
> > 
> > [*] https://ww1.microchip.com/downloads/en/DeviceDoc/80000700A.pdf
> > 
> > Signed-off-by: Stefan Agner <stefan@...er.ch>
> > Acked-by: Marcel Ziswiler <marcel.ziswiler@...adex.com>
> > Signed-off-by: Francesco Dolcini <francesco.dolcini@...adex.com>
> 
> Is this the correct fixes tag?
> 
> Fixes: 1a5465f5d6a2 ("phy/micrel: Add suspend/resume support to Micrel PHYs")
The errata is from 2016, while this commit is from 2013, weird? Apart of that I
can add the Fixes tag, should we send this also to stable?

> Should we leave a comment in place of the callbacks referring 
> to the errata?
I think is a good idea, I'll add it.

Francesco