linux-kernel - Re: [PATCH V6] PCI: Add support for preserving boot configuration

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Date: Sun, 21 Apr 2024 14:03:24 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Vidya Sagar <vidyas@...dia.com>
Cc: bhelgaas@...gle.com, rafael@...nel.org, lenb@...nel.org,
	will@...nel.org, lpieralisi@...nel.org, kw@...ux.com,
	robh@...nel.org, frowand.list@...il.com, linux-pci@...r.kernel.org,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	treding@...dia.com, jonathanh@...dia.com, kthota@...dia.com,
	mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH V6] PCI: Add support for preserving boot configuration

On Thu, Apr 18, 2024 at 11:10:43PM +0530, Vidya Sagar wrote:
> Add support for preserving the boot configuration done by the
> platform firmware per host bridge basis, based on the presence of
> 'linux,pci-probe-only' property in the respective PCI host bridge
> device-tree node. It also unifies the ACPI and DT based boot flows
> in this regard.

This looks great; my only comments are:

  - It might make sense to move the _DSM evaluation to pci-acpi.c
    instead of probe.c.

  - There are a few different things going on (move _DSM, look at DT
    host bridge in addition to of_chosen, integrate ACPI and DT flows,
    tweak usage of PCI_PROBE_ONLY vs bridge->preserve_config, use
    pci_assign_unassigned_root_bus_resources() when we didn't before),
    and I think they could be split into multiple patches to make it
    easier to read.

I took a stab at splitting this, but didn't quite complete it.  I'll
post that as v7-incomplete, and if you compare with v6, you'll see
what's missing (the PCI_PROBE_ONLY and assign resources stuff --
there's some subtlety there that wasn't obvious to me).

Bjorn