Re: [PATCH net V2 1/1] net: phy: fix invalid phy id when probe using C22 - Russell King

From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
To: Florian Fainelli <f.fainelli@gmail.com>
Cc: Heiner Kallweit <hkallweit1@gmail.com>,
	Wong Vee Khee <vee.khee.wong@intel.com>,
	Andrew Lunn <andrew@lunn.ch>,
	"David S . Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	stable@vger.kernel.org, Voon Weifeng <weifeng.voon@intel.com>,
	Ong Boon Leong <boon.leong.ong@intel.com>
Subject: Re: [PATCH net V2 1/1] net: phy: fix invalid phy id when probe using C22
Date: Thu, 18 Mar 2021 16:21:20 +0000	[thread overview]
Message-ID: <20210318162120.GR1463@shell.armlinux.org.uk> (raw)
In-Reply-To: <c921bf7f-e4d1-eefa-c5ae-024d5e8a4845@gmail.com>

On Thu, Mar 18, 2021 at 09:02:22AM -0700, Florian Fainelli wrote:
> On 3/18/2021 6:25 AM, Heiner Kallweit wrote:
> > On 18.03.2021 10:09, Wong Vee Khee wrote:
> >> When using Clause-22 to probe for PHY devices such as the Marvell
> >> 88E2110, PHY ID with value 0 is read from the MII PHYID registers
> >> which caused the PHY framework failed to attach the Marvell PHY
> >> driver.
> >>
> >> Fixed this by adding a check of PHY ID equals to all zeroes.
> >>
> > 
> > I was wondering whether we have, and may break, use cases where a PHY,
> > for whatever reason, reports PHY ID 0, but works with the genphy
> > driver. And indeed in swphy_read_reg() we return PHY ID 0, therefore
> > the patch may break the fixed phy.
> > Having said that I think your patch is ok, but we need a change of
> > the PHY ID reported by swphy_read_reg() first.
> > At a first glance changing the PHY ID to 0x00000001 in swphy_read_reg()
> > should be sufficient. This value shouldn't collide with any real world
> > PHY ID.
> 
> It most likely would not, but it could be considered an ABI breakage,
> unless we filter out what we report to user-space via SIOGCMIIREG and
> /sys/class/mdio_bus/*/*/phy_id
> 
> Ideally we would have assigned an unique PHY OUI to the fixed PHY but
> that would have required registering Linux as a vendor, and the process
> is not entirely clear to me about how to go about doing that.

Doesn't that also involve yearly fees?

-- 
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