linux-kernel - Re: [PATCH net-next v2 4/6] net: mdio: scan bus based on bus capabilities for C22 and C45

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Date:   Sat, 11 Mar 2023 17:11:08 +0100
From:   Klaus Kudielka <klaus.kudielka@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Michael Walle <michael@...le.cc>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Felix Fietkau <nbd@....name>,
        John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Bryan Whitehead <bryan.whitehead@...rochip.com>,
        UNGLinuxDriver@...rochip.com,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-aspeed@...ts.ozlabs.org,
        Jesse Brandeburg <jesse.brandeburg@...el.com>
Subject: Re: [PATCH net-next v2 4/6] net: mdio: scan bus based on bus
 capabilities for C22 and C45

On Sat, 2023-03-11 at 16:39 +0100, Andrew Lunn wrote:
> 
> I have one more idea which can speed things up. The scanning of the
> MDIO bus works in two different ways depending on if there is a DT
> node, describing what should be found on the bus. For mv88e6xxx, using
> DT is optional. Some boards do, some don't.
> 
> If there is a DT node, only the addresses listed in DT are scanned.

Here's the definition of the switch in the Turris Omnia device tree.

	/* Switch MV88E6176 at address 0x10 */
	switch@10 {
		pinctrl-names = "default";
		pinctrl-0 = <&swint_pins>;
		compatible = "marvell,mv88e6085";
		#address-cells = <1>;
		#size-cells = <0>;

		dsa,member = <0 0>;
		reg = <0x10>;

		interrupt-parent = <&gpio1>;
		interrupts = <13 IRQ_TYPE_LEVEL_LOW>;

		ports {
			#address-cells = <1>;
			#size-cells = <0>;

			ports@0 {
				reg = <0>;
				label = "lan0";
			};

			ports@1 {
				reg = <1>;
				label = "lan1";
			};

			ports@2 {
				reg = <2>;
				label = "lan2";
			};

			ports@3 {
				reg = <3>;
				label = "lan3";
			};

			ports@4 {
				reg = <4>;
				label = "lan4";
			};

			ports@5 {
				reg = <5>;
				label = "cpu";
				ethernet = <&eth1>;
				phy-mode = "rgmii-id";

				fixed-link {
					speed = <1000>;
					full-duplex;
				};
			};

			ports@6 {
				reg = <6>;
				label = "cpu";
				ethernet = <&eth0>;
				phy-mode = "rgmii-id";

				fixed-link {
					speed = <1000>;
					full-duplex;
				};
			};
		};

> 
> If there is no DT node, by default, all 32 addresses on the bus are
> scanned. However, DSA makes another assumption. There is a one to one
> mapping between port number and PHY address on the MDIO bus. Port 0
> uses MDIO address 0. Port 7 uses MDIO address 7 etc. If you have an 8
> port switch, there is no point scanning addresses 8 to 31, they will
> never be used.
> 
> The mdio bus structure has a member phy_mask. This is a bitmap. If bit
> N is set, address N is not scanned. So i suggest you extend
> mv88e6xxx_mdio_register() to set phy_mask based on
> mv88e6xxx_num_ports(chip).
> 

What you are proposing here would not show any improvement on the
Omnia, as only the 6 ports would be scanned - right? 

>         Andrew