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

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Date:   Sun, 12 Mar 2023 16:15:41 +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 Sun, 2023-03-12 at 10:04 +0100, Klaus Kudielka wrote:
> On Sun, 2023-03-12 at 03:53 +0100, Andrew Lunn wrote:
> > 
> > Correct. But their also should not of been any noticeable slow down,
> > because there should not be any additional scanning when everything is
> > described in DT. And the move of the MDIO bus registration from probe
> > to setup should actually make it faster than before.
> > 
> 
> But then, why *do* I see such a big difference on the Omnia?
> 
> mdiobus_scan_bus_c45() takes:
> ~2.7 seconds without phy_mask patch
> ~0.2 seconds with phy_mask patch

Following up myself, the answer is in the call path
mv88e6xxx_mdios_register()
	 -> mv88e6xxx_mdio_register()
		-> of_mdiobus_register()

A child node "mdio" would be needed for the scan to be limited by
the device tree. And this one is *not* in armada-385-turris-omnia.dts.

My (incorrect) understanding was, the child node "ports" would trigger
that behaviour.

Best regards, Klaus