netdev - Re: [net-next PATCH v4 06/13] net: dsa: qca8k: move rgmii delay detection to phylink mac

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Date:   Sun, 10 Oct 2021 17:18:16 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Ansuel Smith <ansuelsmth@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Russell King <linux@...linux.org.uk>, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [net-next PATCH v4 06/13] net: dsa: qca8k: move rgmii delay
 detection to phylink mac_config

> > -{
> > -	struct device_node *port_dn;
> > -	phy_interface_t mode;
> > -	struct dsa_port *dp;
> > -	u32 val;
> > -
> > -	/* CPU port is already checked */
> > -	dp = dsa_to_port(priv->ds, 0);
> > -
> > -	port_dn = dp->dn;
> > -
> > -	/* Check if port 0 is set to the correct type */
> > -	of_get_phy_mode(port_dn, &mode);
> > -	if (mode != PHY_INTERFACE_MODE_RGMII_ID &&
> > -	    mode != PHY_INTERFACE_MODE_RGMII_RXID &&
> > -	    mode != PHY_INTERFACE_MODE_RGMII_TXID) {
> > -		return 0;
> > -	}
> > -
> > -	switch (mode) {
> > -	case PHY_INTERFACE_MODE_RGMII_ID:
> > -	case PHY_INTERFACE_MODE_RGMII_RXID:
> 
> Also, since you touch this area.
> There have been tons of discussions on this topic, but I believe that
> your interpretation of the RGMII delays is wrong.
> Basically a MAC should not apply delays based on the phy-mode string (so
> it should treat "rgmii" same as "rgmii-id"), but based on the value of
> "rx-internal-delay-ps" and "tx-internal-delay-ps".
> The phy-mode is for a PHY to use.

There is one exception to this, when the MAC is taking the place of a
PHY, i.e. CPU port. You need delays added somewhere, and the mv88e6xxx
driver will look at the phy-mode in this case. And i think in general,
a DSA driver needs this for the CPU port.

       Andrew