Re: [PATCH net-next v2] net: dsa: microchip: enable SGMII port for KSZ9897

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

Hi Tapio

On 11.8.2026 12:20, Tapio Reijonen wrote:
> The KSZ9897 has an SGMII/1000BASE-X capable port 7, but its chip_info
> entry never set .sgmii_port.

AFAIK only the KSZ9897S variant.  AN5513 says the S "contains the same 
SGMII
port as the KSZ9477 however, the KSZ9897R has a second RGMII port", and
the R data sheet never mentions SGMII at all.

Unfortunately the chip id for both seems to be identical (0x00989700), 
so
this would apply to the R variant too. With this the R variant should
return -ENODEV in ksz9477_pcs_create() during probe.

Have a look how KSZ9563 is split off the KSZ9893 chip id, so maybe it 
can
be solved in a similar manner.  PORT_SGMII_SEL could also be worth a 
look.

> As a result ksz_has_sgmii_port() is false,
> ksz9477_pcs_create() is never called, and 
> ksz9477_phylink_mac_select_pcs()
> returns NULL for port 7, so no PCS is ever instantiated and a
> phy-mode = "sgmii" or "1000base-x" link on that port cannot come up.
> 
> The KSZ9897 shares the KSZ9477 register layout and operations
> (ksz9477_dev_ops, ksz9477_regs) and reaches its port-7 PCS through the
> same SPI-indirect XPCS register window. The register-identical LAN9646
> already enables this via .sgmii_port = 7. Set the same for the KSZ9897
> so the XPCS instance is created and 1000BASE-X / SGMII links on port 7
> negotiate correctly.
> 
> Tested on a KSZ9897 with a 1000BASE-X fibre SFP wired directly to
> port 7: the link negotiates at 1Gbps/full duplex and passes traffic.
> 
> Signed-off-by: Tapio Reijonen <tapio.reijonen@vaisala.com>
> ---
> Changes in v2:
> - Resend only, no functional change: v1 was dropped when the netdev
>   patch queue overflowed.
> - Rebased onto current net-next.
> - Link to v1: 
> https://lore.kernel.org/r/20260703-ksz9897-sgmii-port-v1-1-387e7632dd0b@vaisala.com
> ---
>  drivers/net/dsa/microchip/ksz_common.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/net/dsa/microchip/ksz_common.c 
> b/drivers/net/dsa/microchip/ksz_common.c
> index 
> 1a9d6f83a0232830ac4996ae5f53b8bde0b3747d..a80fde0a8c7e93ea2db4baeb2f941a260e23b687 
> 100644
> --- a/drivers/net/dsa/microchip/ksz_common.c
> +++ b/drivers/net/dsa/microchip/ksz_common.c
> @@ -1484,6 +1484,7 @@ const struct ksz_chip_data ksz_switch_chips[] = {
>  		.internal_phy	= {true, true, true, true,
>  				   true, false, false},
>  		.gbit_capable	= {true, true, true, true, true, true, true},
> +		.sgmii_port = 7,
>  	},
> 
>  	[KSZ9893] = {
> 
> ---
> base-commit: b54074ffb813aa4b97585d97ae1ead69d96432b5
> change-id: 20260703-ksz9897-sgmii-port-48ddb100e015
> 
> Best regards,

Thanks,
Nicolai