linux-kernel - Re: [PATCH 06/15] PCI/ACPI: Link host bridge to its ACPI fw node

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Date:   Wed, 7 Sep 2022 22:15:01 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Robert Richter <rrichter@....com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>, linux-cxl@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Len Brown <lenb@...nel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH 06/15] PCI/ACPI: Link host bridge to its ACPI fw node

On Wed, Sep 7, 2022 at 8:37 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Wed, Aug 31, 2022 at 10:15:54AM +0200, 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.
> >
> > Make this work by linking the host bridge to its ACPI fw node.
>
> s/acpi device/ACPI device/ to match other "ACPI" usage
> s/fw node/fwnode/ (if it should match "fwnode handle" above)
>
> I guess this patch makes ACPI_COMPANION() work where it didn't before,
> right?  E.g., the two ACPI_COMPANION() uses added by this series
> (cxl_find_next_rch() and cxl_restricted_host_probe()).
>
> I'm not really clear on the strategy of when we should use acpi_device
> vs acpi_handle,

acpi_handle should be used for interactions with the ACPICA code, like
when AML is evaluated, and acpi_device for pretty much everything
else.

> but does this mean there's code in places like
> pci_root.c that should be reworked to take advantage of this?  That
> code evaluates _DSM and _OSC, but I think it currently uses
> acpi_handle for that.

That's fine.