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

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Message-ID: <20220914221154.GA710889@bhelgaas>
Date:   Wed, 14 Sep 2022 17:11:54 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Robert Richter <rrichter@....com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, 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 Fri, Sep 09, 2022 at 12:20:45PM +0200, Robert Richter wrote:
> On 08.09.22 12:45:16, Dan Williams wrote:
> > Rafael J. Wysocki wrote:
> > > On Thu, Sep 8, 2022 at 8:05 AM Dan Williams <dan.j.williams@...el.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.

> ...
> No, it is x86. And true, it is set. So this series is actually working
> without this patch. It can be dropped.
> 
> Now, I just checked my logs. The reason I was adding this is that
> during code development I modified the code to have bridge->dev.parent
> set. Then, the fwnode is not linked. I later dropped that change but
> kept this patch.

If this patch does the same thing as the ACPI_COMPANION_SET() in
several pcibios_root_bridge_prepare() implementations, I would love to
keep this patch, which does it in a generic place, and drop the
corresponding code from those arch-specific functions.

But I don't understand the fwnode stuff well enough to know if this is
feasible.

Bjorn