linux-kernel - Re: [PATCH] ARM: mach-imx6q: add ksz9131rn_phy

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Message-ID: <20200305165145.GA25183@lunn.ch>
Date:   Thu, 5 Mar 2020 17:51:45 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     Philippe Schenker <philippe.schenker@...adex.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Allison Randal <allison@...utok.net>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org, NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Fabio Estevam <festevam@...il.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: mach-imx6q: add ksz9131rn_phy_fixup

On Thu, Mar 05, 2020 at 03:38:05PM +0100, Oleksij Rempel wrote:
> Hi Philippe,
> 
> On Thu, Mar 05, 2020 at 02:49:28PM +0100, Philippe Schenker wrote:
> > The MAC of the i.MX6 SoC is compliant with RGMII v1.3. The KSZ9131 PHY
> > is like KSZ9031 adhering to RGMII v2.0 specification. This means the
> > MAC should provide a delay to the TXC line. Because the i.MX6 MAC does
> > not provide this delay this has to be done in the PHY.
> > 
> > This patch adds by default ~1.6ns delay to the TXC line. This should
> > be good for all boards that have the RGMII signals routed with the
> > same length.
> > 
> > The KSZ9131 has relatively high tolerances on skew registers from
> > MMD 2.4 to MMD 2.8. Therefore the new DLL-based delay of 2ns is used
> > and then as little as possibly subtracted from that so we get more
> > accurate delay. This is actually needed because the i.MX6 SoC has
> > an asynchron skew on TXC from -100ps to 900ps, to get all RGMII
> > values within spec.
> 
> This configuration has nothing to do in mach-imx/* It belongs to the
> board devicetree. Please see DT binding documentation for needed
> properties:
> Documentation/devicetree/bindings/net/micrel-ksz90x1.txt

It probably does not even need that. Just

phy-mode = <rgmii-txid>

Also, please Cc: netdev for network code.

      Andrew