netdev - Re: [PATCH v1 net-next] net: phy: mdio_bus: make mdiobus

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Message-ID: <20190826185418.GG2168@lunn.ch>
Date:   Mon, 26 Aug 2019 20:54:18 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Voon Weifeng <weifeng.voon@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jose Abreu <joabreu@...opsys.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Ong Boon Leong <boon.leong.ong@...el.com>
Subject: Re: [PATCH v1 net-next] net: phy: mdio_bus: make mdiobus_scan also
 cover PHY that only talks C45

On Mon, Aug 26, 2019 at 11:27:53AM -0700, Florian Fainelli wrote:
> On 8/26/19 6:52 PM, Voon Weifeng wrote:
> > From: Ong Boon Leong <boon.leong.ong@...el.com>
> > 
> > Make mdiobus_scan() to try harder to look for any PHY that only talks C45.
> If you are not using Device Tree or ACPI, and you are letting the MDIO
> bus be scanned, it sounds like there should be a way for you to provide
> a hint as to which addresses should be scanned (that's
> mii_bus::phy_mask) and possibly enhance that with a mask of possible C45
> devices?

Yes, i don't like this unconditional c45 scanning. A lot of MDIO bus
drivers don't look for the MII_ADDR_C45. They are going to do a C22
transfer, and maybe not mask out the MII_ADDR_C45 from reg, causing an
invalid register write. Bad things can then happen.

With DT and ACPI, we have an explicit indication that C45 should be
used, so we know on this platform C45 is safe to use. We need
something similar when not using DT or ACPI.

	  Andrew