linux-kernel - Re: [PATCH 0/3] PCI & resource: Make coalescing host bridge windows safer

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Message-ID: <20844374-d3df-cc39-a265-44a3008a3bcb@linux.intel.com>
Date: Tue, 21 Oct 2025 14:54:03 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
cc: linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>, 
    Kai-Heng Feng <kaihengf@...dia.com>, Rob Herring <robh@...nel.org>, 
    LKML <linux-kernel@...r.kernel.org>, 
    Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
    Krzysztof Wilczyński <kw@...ux.com>, 
    Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH 0/3] PCI & resource: Make coalescing host bridge windows
 safer

On Tue, 21 Oct 2025, Geert Uytterhoeven wrote:
> On Mon, 20 Oct 2025 at 18:20, Ilpo Järvinen
> <ilpo.jarvinen@...ux.intel.com> wrote:
> > On Mon, 20 Oct 2025, Geert Uytterhoeven wrote:
> > > On Fri, 10 Oct 2025 at 16:42, Ilpo Järvinen
> > > <ilpo.jarvinen@...ux.intel.com> wrote:
> > > > Here's a series for Geert to test if this fixes the improper coalescing
> > > > of resources as was experienced with the pci_add_resource() change (I
> > > > know the breaking change was pulled before 6.18 main PR but I'd want to
> > > > retry it later once the known issues have been addressed). The expected
> > > > result is there'll be two adjacent host bridge resources in the
> > > > resource tree as the different name should disallow coalescing them
> > > > together, and therefore BAR0 has a window into which it belongs to.
> > > >
> > > > Generic info for the series:
> > > >
> > > > PCI host bridge windows were coalesced in place into one of the structs
> > > > on the resources list. The host bridge window coalescing code does not
> > > > know who holds references and still needs the struct resource it's
> > > > coalescing from/to so it is safer to perform coalescing into entirely
> > > > a new struct resource instead and leave the old resource addresses as
> > > > they were.
> > > >
> > > > The checks when coalescing is allowed are also made stricter so that
> > > > only resources that have identical the metadata can be coalesced.
> > > >
> > > > As a bonus, there's also a bit of framework to easily create kunit
> > > > tests for resource tree functions (beyond just resource_coalesce()).
> > > >
> > > > Ilpo Järvinen (3):
> > > >   PCI: Refactor host bridge window coalescing loop to use prev
> > > >   PCI: Do not coalesce host bridge resource structs in place
> > > >   resource, kunit: add test case for resource_coalesce()
> > >
> > > Thanks for your series!
> > >
> > > I have applied this on top of commit 06b77d5647a4d6a7 ("PCI:
> > > Mark resources IORESOURCE_UNSET when outside bridge windows"), and
> > > gave it a a try on Koelsch (R-Car M2-W).
> >
> > So the pci_bus_add_resource() patch to rcar_pci_probe() was not included?
> > No coalescing would be attempted without that change.
> 
> Sorry, I didn't realize you wanted that (and anything else) to be
> included, too.  Please tell me the exact base I should use for testing,
> and I will give it another run.

I'm sorry, it's indeed a bit confusing as some of these patches never 
have been in Linus' tree.

So I'm interested on what's the result with these changes/series together:

[PATCH 1/2] PCI: Setup bridge resources earlier 
[PATCH 2/2] PCI: Resources outside their window must set IORESOURCE_UNSET 
[PATCH 1/1] PCI: rcar-gen2: Add BAR0 into host bridge resources
[PATCH 1/3] PCI: Refactor host bridge window coalescing loop to use prev 
[PATCH 2/3] PCI: Do not coalesce host bridge resource structs in place
[PATCH 3/3] resource, kunit: add test case for resource_coalesce()

You might also want to change that pci_dbg() in the IORESOURCE_UNSET patch 
to pci_info() (as otherwise dyndbg is necessary to make it visible).

Lore links to these series/patches:

https://lore.kernel.org/linux-pci/20250924134228.1663-1-ilpo.jarvinen@linux.intel.com/
https://lore.kernel.org/linux-pci/7640a03e-dfea-db9c-80f5-d80fa2c505b7@linux.intel.com/
https://lore.kernel.org/linux-pci/20251010144231.15773-1-ilpo.jarvinen@linux.intel.com/

The expected result is that those usb resources are properly parented and 
the ee080000-ee08ffff and ee090000-ee090bff are not coalesced together (as 
that would destroy information). So something along the lines of:

    ee080000-ee08ffff : pci@...90000
      ee080000-ee080fff : 0000:00:01.0
        ee080000-ee080fff : ohci_hcd
      ee081000-ee0810ff : 0000:00:02.0
        ee081000-ee0810ff : ehci_hcd
    ee090000-ee090bff : ee090000.pci pci@...90000

-- 
 i.