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

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Message-ID: <20220907183709.GA136851@bhelgaas>
Date:   Wed, 7 Sep 2022 13:37:09 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Robert Richter <rrichter@....com>
Cc:     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@...r.kernel.org, Len Brown <lenb@...nel.org>,
        linux-pci@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH 06/15] PCI/ACPI: Link host bridge to its ACPI fw node

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, 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.

Bjorn