drivers/acpi/pci_root.c | 4 ++++ drivers/acpi/scan.c | 1 + 2 files changed, 5 insertions(+)
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
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@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 For the set: Tested-by: Alison Schofield <alison.schofield@intel.com> Reviewed-by: Alison Schofield <alison.schofield@intel.com>
On Wed, May 27, 2026 at 3:15 AM Alison Schofield <alison.schofield@intel.com> 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@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 > > For the set: > Tested-by: Alison Schofield <alison.schofield@intel.com> > Reviewed-by: Alison Schofield <alison.schofield@intel.com> And so applied as 7.2 material, thanks!
On 5/25/26 7:51 PM, 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@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(+) > For the series Reviewed-by: Dave Jiang <dave.jiang@intel.com> Are Fixes tags needed?
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