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

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Date:   Thu, 18 Aug 2022 01:29:18 +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 9:20
> 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
> 
> > Hi Andrew,
> >
> > 	Your suggestion is indeed an effective solution, but I checked both
> > the datasheet and the driver of AR803x PHYs and found that the
> > qca,clk-out-frequency and the qca,keep-pll-enabled properties are associated
> with the CLK_25M pin of AR803x PHYs.
> > But there is a case that CLK_25M pin is not used on some platforms.
> > Taking our i.MX8DXL platform as an example, the stmmac and AR8031 PHY
> > are applied on this platform, but the CLK_25M pin of AR8031 is not
> > used. So when I used the method you mentioned above, it did not work
> > as expected. In this case, we can only disable the hibernation mode of
> > AR803x PHYs and keep the RX_CLK always outputting a valid clock so that the
> stmmac can complete the software reset operation.
> 
> What happens to the RX_CLK when you unplug the cable? It is no longer
> receiving anything, so i would expect the RX_CLK to stop ticking. Does that
> cause problems for the MAC?
> 
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.

>      Andrew