On 3/18/2021 11:14 AM, Greg KH wrote: > 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. > > If you need me to do that under the umbrella of the Linux Foundation, > I'll be glad to do so if you point me at the proper group to do that > with. > > We did this for a few years with the USB-IF and have a vendor id > assigned to us for Linux through them, until they kicked us out because. > But as the number is in a global namespace, it can't be reused so we > keep it :) We would still be creating what is technically an user-space interface breakage since prior to a given kernel version we would return 0 for that PHY OUI, and after another point it would be something different. I don't know what software out there may be expecting to find 0 and not determine that the PHY was fixed already because it is under /sys/class/mdio_bus/fixed-0 -- Florian
