netdev - Re: [PATCH net-next 3/3] net: phy: mscc: implement RGMII skew delay configuration

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Message-ID: <20200227155128.GB5245@lunn.ch>
Date:   Thu, 27 Feb 2020 16:51:28 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Antoine Tenart <antoine.tenart@...tlin.com>
Cc:     davem@...emloft.net, f.fainelli@...il.com, hkallweit1@...il.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        foss@...il.net
Subject: Re: [PATCH net-next 3/3] net: phy: mscc: implement RGMII skew delay
 configuration

On Thu, Feb 27, 2020 at 04:28:59PM +0100, Antoine Tenart wrote:
> This patch adds support for configuring the RGMII skews in Rx and Tx
> thanks to properties defined in the device tree.

Hi Antoine

What you are not handling here in this patchset is the four RGMII
modes, and what they mean in terms of delay:

        PHY_INTERFACE_MODE_RGMII,
        PHY_INTERFACE_MODE_RGMII_ID,
        PHY_INTERFACE_MODE_RGMII_RXID,
        PHY_INTERFACE_MODE_RGMII_TXID,

The PHY driver should be adding delays based on these
values. Generally, that is enough to make the link work. You only need
additional skew in DT when you need finer grain control than what
these provide.

      Andrew