Re: [PATCH 2/2] ACPI: scan: Honor _DEP for ACPI0016 PCI/CXL host bridge

[Rafael J. Wysocki]

On Tue, May 26, 2026 at 4:51 AM Chen Pei <cp0613@xxxxxxxxxxxxxxxxx> wrote:
>
> CXL root devices (ACPI0017) declare _DEP on their parent ACPI0016
> PCI/CXL host bridge so that cxl_acpi probes only after acpi_pci_root
> has attached the PCI root and registered it for acpi_pci_find_root().
> However, acpi_dev_ready_for_enumeration() only consults dep_unmet
> when the supplier's HID is on acpi_honor_dep_ids[]; otherwise the
> dependency is silently ignored.
>
> Without honoring the dependency, cxl_acpi can probe before the PCI
> root is ready. The resulting CXL topology is broken: decoder targets
> read as 0 and no port/endpoint devices appear under
> /sys/bus/cxl/devices/.
>
> Add ACPI0016 to acpi_honor_dep_ids[] so the _DEP declared by ACPI0017
> is enforced. This relies on the preceding patch ("ACPI: PCI: clear
> _DEP dependencies after PCI root bridge attach"), which releases the
> dependency once the PCI root is fully enumerated; the two patches
> must be applied together.
>
> Signed-off-by: Chen Pei <cp0613@xxxxxxxxxxxxxxxxx>
> ---
>  drivers/acpi/scan.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> index 530547cda8b2..5f20e7748f36 100644
> --- a/drivers/acpi/scan.c
> +++ b/drivers/acpi/scan.c
> @@ -866,6 +866,7 @@ static const char * const acpi_honor_dep_ids[] = {
>         "RSCV0005", /* RISC-V SBI MPXY MBOX */
>         "RSCV0006", /* RISC-V RPMI SYSMSI */
>         "PNP0C0F",  /* PCI Link Device */
> +       "ACPI0016", /* CXL/PCIe host bridge: CXL root (ACPI0017) depends on PCI root attach */
>         NULL
>  };
>
> --

If anyone has any objections or comments on this one, please let me
know.  In the absence of any, it will be queued up (as 7.2 material)
next week.

Thanks!