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

[Rafael J. Wysocki]

On Wed, May 27, 2026 at 3:15 AM Alison Schofield
<alison.schofield@xxxxxxxxx> wrote:
>
> On Tue, May 26, 2026 at 10:51:16AM +0800, Chen Pei wrote:
> > 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@xxxxxxxxxxxxxxxxx/
> >
> > Chen Pei (2):
> >   ACPI: PCI: clear _DEP dependencies after PCI root bridge attach
> >   ACPI: scan: honor _DEP for ACPI0016 PCI/CXL host bridge
>
> For the set:
>         Tested-by: Alison Schofield <alison.schofield@xxxxxxxxx>
>         Reviewed-by: Alison Schofield <alison.schofield@xxxxxxxxx>

And so applied as 7.2 material, thanks!