[PATCH 0/2] Add UCSI I2C transport driver for ITE885x USB-C controllers

[Edward Blair <edward.blair@gmail.com>]

ASUS Z690/Z790/X670E motherboards use ITE8853 (and related ITE8800-ITE8805)
USB Type-C controllers that implement UCSI over I2C. These are currently
unsupported in Linux, causing a boot error:

  i2c i2c-1: Failed to register i2c client ITE8853:00 at 0x40 (-16)

The BIOS on these boards declares two ACPI devices for the same physical
hardware at the same I2C address: a generic UCSI device (MSFT8000) and a
vendor-specific device (ITE8853). The generic device registers first during
ACPI enumeration, blocking the vendor-specific one with -EBUSY. The ITE8853
ACPI device carries the GPIO interrupt resource needed for proper operation,
while MSFT8000 does not.

Patch 1 fixes the i2c ACPI enumeration to skip known generic devices when a
vendor-specific sibling exists at the same address. This is a general fix
that could benefit other platforms with the same BIOS pattern.

Patch 2 adds the ITE885x UCSI transport driver, modeled after ucsi_stm32g0.c.
The only device-specific quirk is that PPM_RESET is handled internally by the
ITE8853 and must not be sent over I2C.

Tested on ASUS ROG Strix Z790-E Gaming WiFi:
  - Boot error eliminated
  - /sys/class/typec/port0 registered successfully
  - UCSI commands complete within one polling cycle (~50ms)
  - USB-C device attach/detach detected with partner enumeration
  - USB Power Delivery negotiation functional
  - SuperSpeed Plus Gen 2x1 devices operational through UCSI-managed port

No MAINTAINERS entry is added as the driver falls under the existing
USB TYPEC UCSI section. Happy to add one if preferred.

Edward Blair (2):
  i2c: acpi: skip generic I2C device when vendor-specific sibling exists
  usb: typec: ucsi: add ITE885x I2C transport driver

 drivers/i2c/i2c-core-acpi.c       |  88 +++++++++
 drivers/usb/typec/ucsi/Kconfig    |  11 ++
 drivers/usb/typec/ucsi/Makefile   |   1 +
 drivers/usb/typec/ucsi/ucsi_ite.c | 285 ++++++++++++++++++++++++++++++
 4 files changed, 385 insertions(+)
 create mode 100644 drivers/usb/typec/ucsi/ucsi_ite.c

-- 
2.53.0