netdev - Re: [PATCH net-next 07/13] net: dsa: sja1105: always keep RGMII ports in the MAC role

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Date:   Mon, 24 May 2021 19:24:10 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH net-next 07/13] net: dsa: sja1105: always keep RGMII ports
 in the MAC role



On 5/24/2021 4:22 PM, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@....com>
> 
> In SJA1105, the xMII Mode Parameters Table field called PHY_MAC denotes
> the 'role' of the port, be it a PHY or a MAC. This makes a difference in
> the MII and RMII protocols, but RGMII is symmetric, so either PHY or MAC
> settings result in the same hardware behavior.
> 
> The SJA1110 is different, and the RGMII ports only work when configured
> in MAC mode, so keep the port roles in MAC mode unconditionally.
> 
> Why we had an RGMII port in the PHY role in the first place was because
> we wanted to have a way in the driver to denote whether RGMII delays
> should be applied based on the phy-mode property or not. This is already
> done in sja1105_parse_rgmii_delays() based on an intermediary
> struct sja1105_dt_port (which contains the port role). So it is a
> logical fallacy to use the hardware configuration as a scratchpad for
> driver data, it isn't necessary.
> 
> We can also remove the gating condition for applying RGMII delays only
> for ports in the PHY role. The .setup_rgmii_delay() method looks at
> the priv->rgmii_rx_delay[port] and priv->rgmii_tx_delay[port] properties
> which are already populated properly (in the case of a port in the MAC
> role they are false). Removing this condition generates a few more SPI
> writes for these ports (clearing the RGMII delays) which are perhaps
> useless for SJA1105P/Q/R/S, where we know that the delays are disabled
> by default. But for SJA1110, the firmware on the embedded microcontroller
> might have done something funny, so it's always a good idea to clear the
> RGMII delays if that's what Linux expects.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
-- 
Florian