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References: <20220831081603.3415-1-rrichter@amd.com> <20220831081603.3415-7-rrichter@amd.com>
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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Thu, 8 Sep 2022 15:06:16 +0200
Message-ID: <CAJZ5v0iQNSNzO+mw7zqkvpniiYdipprTYnkzx-M7Jxq4_Cs8VQ@mail.gmail.com>
Subject: Re: [PATCH 06/15] PCI/ACPI: Link host bridge to its ACPI fw node
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     Robert Richter <rrichter@amd.com>,
        Alison Schofield <alison.schofield@intel.com>,
        Vishal Verma <vishal.l.verma@intel.com>,
        Ira Weiny <ira.weiny@intel.com>,
        Ben Widawsky <bwidawsk@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>, linux-cxl@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Len Brown <lenb@kernel.org>,
        Linux PCI <linux-pci@vger.kernel.org>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>
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On Thu, Sep 8, 2022 at 8:05 AM Dan Williams <dan.j.williams@intel.com> wrote:
>
> Robert Richter wrote:
> > A lookup of a host bridge's corresponding acpi device (struct
> > acpi_device) is not possible, for example:
> >
> >       adev = ACPI_COMPANION(&host_bridge->dev);
> >
> > This could be useful to find a host bridge's fwnode handle and to
> > determine and call additional host bridge ACPI parameters and methods
> > such as HID/CID or _UID.
>
> When is this explicitly needed. "Could be useful" is interesting, but it
> needs to have a practical need.

It is needed and it is present on x86 AFAICS (see my last reply in this thread).

This seems to be addressing an ARM64-specific issue.

> >
> > Make this work by linking the host bridge to its ACPI fw node.
> >
> > Signed-off-by: Robert Richter <rrichter@amd.com>
> > ---
> >  drivers/acpi/pci_root.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> > index d57cf8454b93..846c979e4c29 100644
> > --- a/drivers/acpi/pci_root.c
> > +++ b/drivers/acpi/pci_root.c
> > @@ -1083,6 +1083,7 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
> >               goto out_release_info;
> >
> >       host_bridge = to_pci_host_bridge(bus->bridge);
> > +     host_bridge->dev.fwnode = acpi_fwnode_handle(device);
> >       if (!(root->osc_control_set & OSC_PCI_EXPRESS_NATIVE_HP_CONTROL))
> >               host_bridge->native_pcie_hotplug = 0;
> >       if (!(root->osc_control_set & OSC_PCI_SHPC_NATIVE_HP_CONTROL))
> > --
> > 2.30.2
> >
>
>