Re: [PATCH net-next 3/3] net: mdio: mdio-bcm-unimac: Add Clause 45 support

[Nicolai Buchwitz <nb@tipi-net.de>]

Hi Florian

On 13.11.2026 22:15, Florian Fainelli wrote:
> Add Clause 45 read/write support to the UniMAC MDIO bus controller 
> driver
> by implementing the read_c45/write_c45 bus callbacks. Each access 
> performs
> the two-step C45 sequence (ADDR cycle followed by a READ/WRITE cycle) 
> under
> the bus lock and switches MDIO_CFG between C22 and C45 mode as needed;
> MDIO_CFG is only written when the mode actually changes.
> 
> Also skip the BMSR workaround read in unimac_mdio_reset() for children
> compatible with "ethernet-phy-ieee802.3-c45", since such PHYs are not
> expected to respond to C22 accesses.
> 
> Note that providing read_c45/write_c45 also makes the MDIO core scan 
> for
> C45 PHYs at registration time, on addresses that are not masked and do 
> not
> already have a C22 device.
> 
> Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
> Co-developed-by: Carlos Soto <carlos.soto@broadcom.com>
> Signed-off-by: Carlos Soto <carlos.soto@broadcom.com>
> Co-developed-by: Justin Chen <justin.chen@broadcom.com>
> Signed-off-by: Justin Chen <justin.chen@broadcom.com>
> ---
>  drivers/net/mdio/mdio-bcm-unimac.c | 105 +++++++++++++++++++++++++++--
>  1 file changed, 98 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/mdio/mdio-bcm-unimac.c 
> b/drivers/net/mdio/mdio-bcm-unimac.c

> [...]

> @@ -301,6 +390,8 @@ static int unimac_mdio_probe(struct platform_device 
> *pdev)
>  	bus->parent = &pdev->dev;
>  	bus->read = unimac_mdio_read;
>  	bus->write = unimac_mdio_write;
> +	bus->read_c45 = unimac_mdio_read_c45;
> +	bus->write_c45 = unimac_mdio_write_c45;

AFAIU this breaks GENET without DT (e.g. Pi 4 with ACPI). Arguably an 
edge case,
but last time I tried it worked at least. With your changes all 
addresses get
a C45 scan there for which the empty ones return -EIO. get_phy_c45_ids() 
passes
that up instead of mapping it to -ENODEV like the C22 path.

A cheap fix would be to do the same mapping in get_phy_c45_ids() as we 
have for C22.

Thanks,
Nicolai