net: phy: sfp: Add support for SMBus module access

The SFP module's eeprom and internals are accessible through an i2c bus.

It is possible that the SFP might be connected to an SMBus-only
controller, such as the one found in some PHY devices in the VSC85xx
family.

Introduce a set of sfp read/write ops that are going to be used if the
i2c bus is only capable of doing smbus byte accesses.

As Single-byte SMBus transaction go against SFF-8472 and breaks the
atomicity for diagnostics data access, hwmon is disabled in the case
of SMBus access.

Moreover, as this may cause other instabilities, print a warning at
probe time to indicate that the setup may be unreliable because of the
hardware design.

As hwmon may be disabled for both broken EEPROM and smbus, the warnings
are udpated accordingly.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250322075745.120831-2-maxime.chevallier@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions