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:   Thu, 9 Mar 2023 17:36:25 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Klaus Kudielka <klaus.kudielka@...il.com>
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 Wed, Mar 08, 2023 at 07:34:40PM +0100, Klaus Kudielka wrote:
> On Tue, 2023-03-07 at 21:35 +0100, Andrew Lunn wrote:
> > > Summary: Still 4 calls to mdio_bus_scan_c22, but also *2* calls to mdio_bus_scan_c45, approx. 190*100 reads by the switch driver

I was wrong about something i said earlier. A C22 scan reads two
registers for each of the 32 possible locations of a C22 PHY on the
bus. A C45 scan is however much more expensive. It will read 30 time
two registers for each of the 32 possible locations of a C45 PHY on
the bus.

One things that could help is moving some code around a bit. Currently
mv88e6xxx_mdios_register() is called at the end of
mv88e6xxx_probe(). Try moving it to the beginning of
mv88e6xxx_setup(). The call to mv88e6xxx_mdios_unregister() then need
to move into mv88e6xxx_teardown().

	Andrew