netdev - Re: [PATCH] of: of_mdio: count number of regitered phys

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Message-ID: <20200630004543.GB597495@lunn.ch>
Date:   Tue, 30 Jun 2020 02:45:43 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Claudiu Beznea <claudiu.beznea@...rochip.com>
Cc:     f.fainelli@...il.com, hkallweit1@...il.com, linux@...linux.org.uk,
        robh+dt@...nel.org, frowand.list@...il.com, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] of: of_mdio: count number of regitered phys

On Mon, Jun 29, 2020 at 10:26:36AM +0300, Claudiu Beznea wrote:
> In case of_mdiobus_register_phy()/of_mdiobus_register_device()
> returns -ENODEV for all PHYs in device tree or for all scanned
> PHYs there is a chance that of_mdiobus_register() to
> return success code although no PHY devices were registered.
> Add a counter that increments every time a PHY was registered
> to avoid the above scenario.

Hi Claudiu

There is a danger here this will break something. Without this patch,
an empty bus is O.K. But with this patch, a bus without a PHY is a
problem.

Take for example FEC. It often comes in pairs. Each has an MDIO
bus. But to save pins, there are some designs which place two PHYs on
one bus, leaving the other empty. The driver unconditionally calls
of_mdiobus_register() and if it returns an error, it will error out
the probe. So i would not be too surprised if you get reports of
missing interfaces with this patch.

	Andrew