linux-kernel - Re: [PATCH net-next v3] net: phy: micrel: add phy-mode support for the KSZ9031 PHY

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Date:   Tue, 28 Apr 2020 17:47:18 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Oleksij Rempel <o.rempel@...gutronix.de>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        David Jander <david@...tonic.nl>,
        "David S. Miller" <davem@...emloft.net>,
        Sascha Hauer <kernel@...gutronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Philippe Schenker <philippe.schenker@...adex.com>,
        Russell King <linux@...linux.org.uk>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH net-next v3] net: phy: micrel: add phy-mode support for
 the KSZ9031 PHY

On Tue, Apr 28, 2020 at 05:28:30PM +0200, Geert Uytterhoeven wrote:
> This triggers on Renesas Salvator-X(S):
> 
>     Micrel KSZ9031 Gigabit PHY e6800000.ethernet-ffffffff:00:
> *-skew-ps values should be used only with phy-mode = "rgmii"
> 
> which uses:
> 
>         phy-mode = "rgmii-txid";
> 
> and:
> 
>         rxc-skew-ps = <1500>;
> 
> If I understand Documentation/devicetree/bindings/net/ethernet-controller.yaml
> correctly:

Hi Geert

Checking for skews which might contradict the PHY-mode is new. I think
this is the first PHY driver to do it. So i'm not too surprised it has
triggered a warning, or there is contradictory documentation.

Your use cases is reasonable. Have the normal transmit delay, and a
bit shorted receive delay. So we should allow it. It just makes the
validation code more complex :-(

	   Andrew