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

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Date:   Thu, 18 Aug 2022 03:44:25 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Wei Fang <wei.fang@....com>
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

> 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?

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