netdev - RE: [PATCH net 1/2] dt: ar803x: Document disable-hibernation property

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Date:   Thu, 18 Aug 2022 02:01:04 +0000
From:   Wei Fang <wei.fang@....com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net 1/2] dt: ar803x: Document disable-hibernation property



> -----Original Message-----
> From: Andrew Lunn <andrew@...n.ch>
> Sent: 2022年8月18日 9:44
> To: Wei Fang <wei.fang@....com>
> Cc: hkallweit1@...il.com; linux@...linux.org.uk; davem@...emloft.net;
> edumazet@...gle.com; kuba@...nel.org; pabeni@...hat.com;
> robh+dt@...nel.org; krzysztof.kozlowski+dt@...aro.org; f.fainelli@...il.com;
> netdev@...r.kernel.org; devicetree@...r.kernel.org;
> linux-kernel@...r.kernel.org
> Subject: Re: [PATCH net 1/2] dt: ar803x: Document disable-hibernation
> property
> 
> > Yes, after the PHY enters hibernation mode that the RX_CLK stop
> > ticking, but for stmmac, it is essential that RX_CLK of PHY is present
> > for software reset completion. Otherwise, the stmmac is failed to
> > complete the software reset and can not init DMA.
> 
> So the RX_CLK is more than the recovered clock from the bit stream on the
> wire. The PHY has a way to generate a clock when there is no bit stream?
> 
Yes, when disable hibernation mode, the RX_CLK always output a valid clock.

> To me, it sounds like your hardware design is wrong, and it should be using the
> 25MHz reference clock. And what you are proposing is a workaround for this
> hardware problem.
> 
> Anyway, i agree with Russell, a DT property is fine. But please make it clear in
> the binding documentation that disabling hibernation has the side affect of
> keeping the RX_CLK ticking when there is no link. That is probably what people
> want this for, not to actual disable hibernation.
> 
> 	Andrew