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

On 18.03.2021 17:02, Florian Fainelli wrote:

On 3/18/2021 6:25 AM, Heiner Kallweit wrote:

quoted

On 18.03.2021 10:09, Wong Vee Khee wrote:

quoted

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.
--

In the OUI list I found entry 58-9C-FC, belonging to FreeBSD Foundation.
Not sure what they use it for, but it seems adding Linux as a vendor
wouldn't be a total exception.

Florian

Heiner