linux-kernel - Re: [net-next PATCH 1/3] dt-bindings: net: ipq4019-mdio: document now supported clock-frequency

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Date: Wed, 24 Jan 2024 23:38:14 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Christian Marangi <ansuelsmth@...il.com>
Cc: Andy Gross <agross@...nel.org>, Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Robert Marko <robert.marko@...tura.hr>,
	linux-arm-msm@...r.kernel.org, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [net-next PATCH 1/3] dt-bindings: net: ipq4019-mdio: document
 now supported clock-frequency

On Wed, Jan 24, 2024 at 11:27:20PM +0100, Christian Marangi wrote:
> On Wed, Jan 24, 2024 at 11:23:05PM +0100, Andrew Lunn wrote:
> > > +  clock-frequency:
> > > +    description:
> > > +      The MDIO bus clock that must be output by the MDIO bus hardware, if
> > > +      absent, the default hardware values are used.
> > > +
> > > +      MDC rate is feed by an external clock (fixed 100MHz) and is divider
> > > +      internally. The default divider is /256 resulting in the default rate
> > > +      applied of 390KHz.
> > > +    enum: [ 390625, 781250, 1562500, 3125000, 6250000, 12500000 ]
> > 
> > Hi Christian
> > 
> > 802.3 says the clock should be up to 2.5MHz by default. So the nearest
> > would be 1562500. Please document that if not set, it defaults to
> > this. And make the driver actually default to that.
> >
> 
> As I said, this is very fk up and default value is 390KHz unless anyone
> in the chain sets it (sometime uboot does it but it's not that common...
> default qsdk uboot doesn't do that for example)... Ok I have to change
> this to default to 1562500.

I doubt you will cause any regression by defaulting to 2.5HHz
instead. That is what the standard says it should be. All devices on
the bus should support that.

    Andrew