netdev - Re: [PATCH 2/3] net: macb: add support for C45 MDIO read/write

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Message-ID: <20191128145246.GD3420@lunn.ch>
Date:   Thu, 28 Nov 2019 15:52:46 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Milind Parab <mparab@...ence.com>
Cc:     "Nicolas.Ferre@...rochip.com" <Nicolas.Ferre@...rochip.com>,
        "antoine.tenart@...tlin.com" <antoine.tenart@...tlin.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dhananjay Vilasrao Kangude <dkangude@...ence.com>,
        Parshuram Raju Thombare <pthombar@...ence.com>,
        "rmk+kernel@....linux.org.uk" <rmk+kernel@....linux.org.uk>
Subject: Re: [PATCH 2/3] net: macb: add support for C45 MDIO read/write

> This patch doesn't affect current C22 operation of the driver. 
> However if a user selects C45 on incompatible MAC (there are old MAC, prior to Release1p10, released 10th April 2003) MDIO operations may fails.

How do they fail? Lockup the chip and require a cold boot? Timeout
after 10ms and return -ETIMEOUT?

Currently, there is nothing stopping a C45 access to happen. There has
been talk of making the probe for C45 PHYs the same as C22, scan the
bus. I guess that would be implemented by adding a flag to each MDIO
bus driver indicating it supports C45. All 32 addresses would then be
probed using C45 as well as C22. So we need to be sure it is safe to
use C45 on these older devices.

      Andrew