net: sfp: add quirk for XikeStor SKT-2.5G-100M

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This 2.5G copper SFP module contains a RTL8221B-VB-CG PHY which can be
accessed using Rollball protocol.

Add a SFP quirk to enable Rollball protocol. It includes a small delay
to avoid unnecessary attempts at reading PHY registers before the
module is ready.

Note: The RTL8221B PHY in this module becomes stuck in a broken state
after attempting to read some registers on MMD 30 while it has already
established a link (this is a general issue with this PHY which happens
when it is configured for rate adaptation mode). This includes the
registers 2/3/8 which are read by "get_phy_c45_ids" during PHY probing.
However, the PHY takes about 4 seconds to establish a link after reset,
so in practice any host that supports TX_DISABLE should be unaffected,
as that puts the PHY into reset.

Signed-off-by: Jan Hoffmann <jan@3e8.eu>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20260920192632.72729-2-jan@3e8.eu
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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Jan Hoffmann 2026-09-20 21:26:10 +02:00 • committed by Jakub Kicinski

parent 1196e46f6d

commit a9e94a7faa

1 changed files with 15 additions and 0 deletions

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drivers/net/phy/sfp.c

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