On Tue, 9 Jun 2026 at 13:48, Jonathan Cameron <[email protected]> wrote:
>
> On Tue, 2 Jun 2026 15:41:25 +0800
> Chen Pei <[email protected]> wrote:
>
> > On RISC-V QEMU virt platform with CXL enabled, the probe ordering
> > of acpi_pci_root (ACPI0016) and cxl_acpi (ACPI0017) is not
> > guaranteed. If cxl_acpi probes before acpi_pci_root has attached
> > the CXL host bridges, the CXL port topology will be incomplete
> > because to_cxl_host_bridge() silently skips devices whose PCI root
> > is not yet ready.
> >
> > Add a _DEP object to the ACPI0017 device in the DSDT, declaring
> > its dependency on the ACPI0016 CXL host bridge devices. This tells
> > the OS to defer ACPI0017 enumeration until all ACPI0016 devices
> > have been attached by acpi_pci_root.
> >
> > This requires a corresponding kernel change to call
> > acpi_dev_clear_dependencies() in acpi_pci_root_add().
> >
> > Signed-off-by: Chen Pei <[email protected]>
>
> It may be a good idea to add a bios tables test as well.
>
> We only have the x86 q35 one today because I argued at the time
> the ARM64 one would be just duplication. Now we have this new _DEP
> stuff we should probably add something to cover it.
>
> Please also include an iasl -d dump of the relevant additions to DSDT
> in the patch description. Much easier to review than the code that
> generates it!
>
> In general looks fine to me and great that you are clearing this up.
> Seems it's luck that x86 and ARM64 worked without this (or strictly
> speaking other things enforcing the ordering). Ultimately we probably
> want to add this to those two architectures a well.
>
> One small thing inline.
> > +
> > + QLIST_FOREACH(bus, &s->bus->child, sibling) {
> > + if (pci_bus_is_root(bus) && pci_bus_is_cxl(bus)) {
> > + num_cxl_hbs++;
>
> I think you only care if there is at least one. Instead of counting, just set
> a bool and break out early if you find one.
> > + Aml *dep_pkg = aml_package(num_cxl_hbs);
Looks like we need it so we can set the num_elements here.
(If we had a version of aml_package() that let you set the number
of elements after the fact we could do this all with a single loop,
but it doesn't look like we have any other places where that would
be useful. Almost all the callers pass a fixed number.)
-- PMM
