Linux Kernel EUVD-2026-59296

PMBus (Power Management Bus) is an I2C-based protocol for digital power management in server and embedded hardware. The Linux kernel hwmon subsystem's PMBus core driver (drivers/hwmon/pmbus/pmbus_core.c) handles voltage output regulation via VID (Voltage Identifier) encoding tables that differ across standards: VR11, VR12, VR13, and IMVP9. The bug is a classic read/write asymmetry: pmbus_reg2data_vid() (register-to-data, i.e., reads) already performed a switch(data->vrm_version) dispatch, while pmbus_data2reg_vid() (data-to-register, i.e., writes) was hardcoded to VR11 encoding only. Drivers such as the Nvidia PMBUS driver that configure vrm_version to a non-VR11 mode and expose a voltage regulator or hwmon vout setter would encode output voltage targets using the wrong lookup table, producing values that the chip interprets as far higher voltages than intended. The fix mirrors the read path logic into the write path to ensure round-trip consistency. CWE is not formally assigned, but this is functionally a CWE-697 (Incorrect Comparison) or CWE-682 (Incorrect Calculation) - an incorrect encoding table selection leading to wrong output values.