[PATCH 0/2] ACPI/PCI/CXL: Enforce _DEP ordering between ACPI0016 and ACPI0017

[Chen Pei <cp0613@linux.alibaba.com>]

On platforms whose ACPI namespace exposes a CXL host bridge (ACPI0016)
with an ACPI0017 CXL root device declaring _DEP on the host bridge,
cxl_acpi can probe before acpi_pci_root has attached the PCI root.
acpi_pci_find_root() then returns NULL, decoder targets read as 0,
and no port/endpoint device shows up under /sys/bus/cxl/devices/.

The root cause is twofold:

  1. acpi_pci_root_add() never calls acpi_dev_clear_dependencies(),
     so _DEP suppliers downstream of a PCI root are never released.

  2. ACPI0016 is not on acpi_honor_dep_ids[], so even when ACPI0017
     declares _DEP on it, acpi_dev_ready_for_enumeration() bypasses
     the dep_unmet check and lets cxl_acpi probe early.

On x86 the bug is usually masked by link order (acpi_pci_root is
built in and probed before cxl_acpi). On architectures like RISC-V
that ordering is not guaranteed, so the standard ACPI _DEP mechanism
must actually work.

This series fixes both sides and the two patches must be applied
together; applying only patch 2 would prevent cxl_acpi from ever
probing on ACPI0016 systems, because the supplier would never clear
the dependency.

  Patch 1 makes acpi_pci_root_add() clear _DEP on the supplier once
          the PCI root bus has been added.
  Patch 2 adds ACPI0016 to acpi_honor_dep_ids[] so the dependency
          declared by ACPI0017 is enforced.

The approach in this series follows the discussion of an earlier
posting:
https://lore.kernel.org/linux-cxl/20260514023238.49984-1-cp0613@linux.alibaba.com/

Chen Pei (2):
  ACPI: PCI: clear _DEP dependencies after PCI root bridge attach
  ACPI: scan: honor _DEP for ACPI0016 PCI/CXL host bridge

 drivers/acpi/pci_root.c | 4 ++++
 drivers/acpi/scan.c     | 1 +
 2 files changed, 5 insertions(+)

-- 
2.50.1