netdev - Re: [PATCH 1/3] ARM: dts: imx51: ZII: Add missing phy-mode

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Date:   Fri, 7 Apr 2023 19:50:34 +0300
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     shawnguo@...nel.org, s.hauer@...gutronix.de,
        Russell King <rmk+kernel@...linux.org.uk>,
        arm-soc <arm@...nel.org>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/3] ARM: dts: imx51: ZII: Add missing phy-mode

On Fri, Apr 07, 2023 at 06:10:31PM +0200, Andrew Lunn wrote:
> On Fri, Apr 07, 2023 at 06:41:59PM +0300, Vladimir Oltean wrote:
> > On Fri, Apr 07, 2023 at 05:25:01PM +0200, Andrew Lunn wrote:
> > > The DSA framework has got more picky about always having a phy-mode
> > > for the CPU port. The imx51 Ethernet supports MII, and RMII. Set the
> > > switch phy-mode based on how the SoC Ethernet port has been
> > > configured.
> > > 
> > > Additionally, the cpu label has never actually been used in the
> > > binding, so remove it.
> > > 
> > > Signed-off-by: Andrew Lunn <andrew@...n.ch>
> > > ---
> > 
> > In theory, an MII MAC-to-MAC connection should have phy-mode = "mii" on
> > one end and phy-mode = "rev-mii" on the other, right?
> 
> In theory, yes. As far as i understand, it makes a difference to where
> the clock comes from. rev-mii is a clock provider i think.
> 
> But from what i understand of the code, and the silicon, this property
> is going to be ignored, whatever value you give it. phy-mode is only
> used and respected when the port can support 1000Base-X, SGMII, and
> above, or use its built in PHY. For MII, GMII, RMII, RGMII the port
> setting is determined by strapping resistors.

If it's ignored, even better, one more reason to make it rev-mii and
not mii, no compatibility concerns with the driver not understanding the
difference...

> The DSA core however does care that there is a phy-mode, even if it is
> ignored. I hope after these patches land we can turn that check into
> enforce mode, and that then unlocks Russell to make phylink
> improvement.
> 
> 	Andrew
>