net: phy: sfp: detect presence via I2C when no MOD_DEF0 GPIO

An SFP cage (compatible "sff,sfp") whose MOD_DEF0 signal is not wired to a
GPIO currently falls back to sff_gpio_get_state(), which unconditionally
reports the module as present. An empty cage therefore fails its probe and
is parked in SFP_MOD_ERROR forever; because SFP_F_PRESENT never deasserts
there is no REMOVE event to recover the state machine, so a module inserted
after boot is never detected, and empty cages spam -EIO at boot.

This affects boards that route none of the cage presence signal to a
software-readable input. On the NicGiga S100-0800S-M (RTL9303, 8x SFP+) the
cage I2C bus is the switch's SMBus master; TX_DISABLE is driven via a
PCA9534 I/O expander, but no MOD_ABS/MOD_DEF0 line reaches a readable GPIO
(the RTL9303 gpio0 lines read stuck-low, the single PCA9534 is fully
consumed by TX_DISABLE, and there is no RTL8231). The Horaco ZX-SW82TS-L2P
(RTL9302D, 2x SFP+) is independently affected in the same way.

For such an SFP cage, derive presence from a throttled single-byte I2C read
of the module EEPROM instead: a successful read asserts SFP_F_PRESENT,
R_PROBE_ABSENT consecutive failures clear it (to ride out a transient error
on a live module). The existing poll then emits SFP_E_INSERT / SFP_E_REMOVE
normally, giving working hot-plug and silencing the boot-time -EIO spam on
empty cages. Presence is re-probed every T_PROBE_PRESENT, so insertion is
detected within that interval and removal within
T_PROBE_PRESENT * R_PROBE_ABSENT.

A soldered-down module (compatible "sff,sff") has no presence signal and is
genuinely always present, so it continues to use sff_gpio_get_state(); the
new path is gated on the cage type advertising SFP_F_PRESENT.

Signed-off-by: Greg Patrick <gregspatrick@hotmail.com>
Tested-by: Manuel Stocker <mensi@mensi.ch>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Tested-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20260611175341.2223184-1-gregspatrick@hotmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions