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

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Date:   Mon, 15 Aug 2022 06:49:39 +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12日 22:15
> 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
> 
> On Sat, Aug 13, 2022 at 12:50:08AM +1000, wei.fang@....com wrote:
> > From: Wei Fang <wei.fang@....com>
> >
> > The hibernation mode of Atheros AR803x PHYs is default enabled.
> > When the cable is unplugged, the PHY will enter hibernation mode and
> > the PHY clock does down. For some MACs, it needs the clock to support
> > it's logic. For instance, stmmac needs the PHY inputs clock is present
> > for software reset completion. Therefore, It is reasonable to add a DT
> > property to disable hibernation mode.
> 
> It is not the first time we have seen this. What you should really be
> concentrating on is the clock out. That is what the MAC requires here.
> 
> You already have the property qca,clk-out-frequency. You could maybe piggy
> back off this. If that property is being used, you know the clock output is used. So
> you should do what is needed to keep it ticking.
> 
> You also have qca,keep-pll-enabled:
> 
>       If set, keep the PLL enabled even if there is no link. Useful if you
>       want to use the clock output without an ethernet link.
> 
> To me, it seems like you already have enough properties, you just need to imply
> that you need to disable hibernation in order to fulfil these properties.
> 
> 	Andrew

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.