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

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Date:   Fri, 12 Aug 2022 15:04:41 +0300
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Wei Fang <wei.fang@....com>, "andrew@...n.ch" <andrew@...n.ch>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "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

On 12/08/2022 14:36, Russell King (Oracle) wrote:
> On Fri, Aug 12, 2022 at 02:25:42PM +0300, Krzysztof Kozlowski wrote:
>> hibernation is a feature, but 'disable-hibernation' is not. DTS
>> describes the hardware, not policy or driver bejhvior. Why disabling
>> hibernation is a property of hardware? How you described, it's not,
>> therefore either property is not for DT or it has to be phrased
>> correctly to describe the hardware.
> 
> However, older DT descriptions need to be compatible with later kernels,
> and as existing setups have hibernation enabled, introducing a property
> to _enable_ hibernation (which implies if the property is not present,
> hibernation is disabled) changes the behaviour with older DT, thereby
> breaking backwards compatibility.
> 
> Yes, DT needs to describe hardware, but there are also other
> constraints too.

I did not propose a property to enable hibernation. The property must
describe hardware, so this piece is missing, regardless whether the
logic in the driver is "enable" or "disable".

The hardware property for example is: "broken foo, so hibernation should
be disabled" or "engineer forgot to wire cables, so hibernation won't
work"...

Best regards,
Krzysztof