Re: [PATCH RFC net-next] net: phy: sfp: drop 1000Base-T support for FCLF8521P2BTL

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

On 7/14/26 14:49, Michael Walle wrote:
> The FCLF8521P2BTL is marketed as a drop in replacement for fiber
> modules using 1000Base-X autoneg towards the host as default. See the
> referenced application note, esp. question #11. Drop the 1000baseT
> capability, so 1000Base-X will eventually be used.
> 
> This is esp. important if the TX_DISABLE pin is not connected on a
> board. Usually, pin is used as a reset line to the PHY on the copper
> SFP. If a bootloader expects the default mode and doesn't do any
> reconfiguration of the SFP module, a link might not be established.
> 
> Link: https://www.coherent.com/resources/application-note/networking/1000base-t-sfp-faq-an-2036.pdf
> Signed-off-by: Michael Walle <mwalle@kernel.org>
> ---
> I'm not sure, this is the correct place for the fix, nor if it goes in
> the right direction. There is a comment in
> 
> /*
>  * Clause 22 copper SFP modules normally operate in Cisco SGMII mode with
>  * negotiation enabled, but some may be in 1000base-X - which is for the
>  * PHY driver to determine.
>  */
> 
> I haven't found any traces of that though. So any pointers, what flags
> have to be modified is appreciated (phydev->supported?
> phydev->possible_interfaces?).

Well I've tried in the past to change the resolution of the phy_interface_t
for a module, possible_interfaces won't work as this is populated too late
(at config init time), and we do the SFP interface resolution before that.

What we need is for PHYs to expose the list of interfaces they support at
drive-probe time.

Thing is, Russell has code for that :

http://git.armlinux.org.uk/cgit/linux-arm.git/log/?h=net-queue

but that code isn't upstream. I've tried to ask multiple times how we should
go forward with that, but with no reply :

https://lore.kernel.org/netdev/20260114225731.811993-3-maxime.chevallier@bootlin.com/

Russell's supported_interfaces approach works, I'm using that for SGMII to 100FX
modules, but the question is "how do we upstream that", especially with Russell
being away at the time :(

Maxime