This is a 2.5G copper module which appears to be based on a Motorcomm
YT8821 PHY. There doesn't seem to be a usable way to to access the PHY
(I2C address 0x56 provides only read-only C22 access, and Rollball is
also not working).

The module does not report the correct extended compliance code for
2.5GBase-T, and instead claims to support SONET OC-48 and Fibre Channel:

  Identifier          : 0x03 (SFP)
  Extended identifier : 0x04 (GBIC/SFP defined by 2-wire interface ID)
  Connector           : 0x07 (LC)
  Transceiver codes   : 0x00 0x01 0x00 0x00 0x40 0x40 0x04 0x00 0x00
  Transceiver type    : FC: Multimode, 50um (M5)
  Encoding            : 0x05 (SONET Scrambled)
  BR Nominal          : 2500MBd

Despite this, the kernel still enables the correct 2500Base-X interface
mode. However, for the module to actually work, it is also necessary to
disable inband auto-negotiation.

Enable the existing "sfp_quirk_oem_2_5g" for this module, which handles
that and also sets the bit for 2500Base-T link mode.

Signed-off-by: Jan Hoffmann <jan@3e8.eu>
---
v2:
 - use "sfp_quirk_oem_2_5g" instead of "sfp_quirk_disable_autoneg"

 drivers/net/phy/sfp.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/phy/sfp.c b/drivers/net/phy/sfp.c
index 5db841377199..0a455a2daccb 100644
--- a/drivers/net/phy/sfp.c
+++ b/drivers/net/phy/sfp.c
@@ -567,6 +567,8 @@ static const struct sfp_quirk sfp_quirks[] = {
 	SFP_QUIRK_F("Turris", "RTSFP-2.5G", sfp_fixup_rollball),
 	SFP_QUIRK_F("Turris", "RTSFP-10", sfp_fixup_rollball),
 	SFP_QUIRK_F("Turris", "RTSFP-10G", sfp_fixup_rollball),
+
+	SFP_QUIRK_S("ZOERAX", "SFP-2.5G-T", sfp_quirk_oem_2_5g),
 };
 
 static size_t sfp_strlen(const char *str, size_t maxlen)
-- 
2.53.0

On Sun, Mar 29, 2026 at 09:11:11PM +0200, Jan Hoffmann wrote:
> This is a 2.5G copper module which appears to be based on a Motorcomm
> YT8821 PHY. There doesn't seem to be a usable way to to access the PHY
> (I2C address 0x56 provides only read-only C22 access, and Rollball is
> also not working).
> 
> The module does not report the correct extended compliance code for
> 2.5GBase-T, and instead claims to support SONET OC-48 and Fibre Channel:
> 
>   Identifier          : 0x03 (SFP)
>   Extended identifier : 0x04 (GBIC/SFP defined by 2-wire interface ID)
>   Connector           : 0x07 (LC)
>   Transceiver codes   : 0x00 0x01 0x00 0x00 0x40 0x40 0x04 0x00 0x00
>   Transceiver type    : FC: Multimode, 50um (M5)
>   Encoding            : 0x05 (SONET Scrambled)
>   BR Nominal          : 2500MBd
> 
> Despite this, the kernel still enables the correct 2500Base-X interface
> mode. However, for the module to actually work, it is also necessary to
> disable inband auto-negotiation.
> 
> Enable the existing "sfp_quirk_oem_2_5g" for this module, which handles
> that and also sets the bit for 2500Base-T link mode.
> 
> Signed-off-by: Jan Hoffmann <jan@3e8.eu>

Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

Thanks!

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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