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

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Message-ID: <CAMuHMdVwAkC0XOU_SZ0HeH0+oT-j5SvKyRcFcJbbes624Yu9uQ@mail.gmail.com>
Date: Mon, 20 Oct 2025 15:42:32 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Kai-Heng Feng <kaihengf@...dia.com>, Rob Herring <robh@...nel.org>, 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>, 
	Linux-Renesas <linux-renesas-soc@...r.kernel.or>
Subject: Re: [PATCH 0/3] PCI & resource: Make coalescing host bridge windows safer

Hi Ilpo,

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).

Impact on dmesg (for the first PCI/USB) instance:

     pci-rcar-gen2 ee090000.pci: host bridge /soc/pci@...90000 ranges:
     pci-rcar-gen2 ee090000.pci:      MEM 0x00ee080000..0x00ee08ffff
-> 0x00ee080000
     pci-rcar-gen2 ee090000.pci: PCI: revision 11
     pci-rcar-gen2 ee090000.pci: PCI host bridge to bus 0000:00
     pci_bus 0000:00: root bus resource [bus 00]
     pci_bus 0000:00: root bus resource [mem 0xee080000-0xee08ffff]
     pci 0000:00:00.0: [1033:0000] type 00 class 0x060000 conventional
PCI endpoint
    -pci 0000:00:00.0: BAR 0 [mem 0xee090800-0xee090bff]: no initial
claim (no window)
     pci 0000:00:00.0: BAR 0 [mem size 0x00000400]
    -pci 0000:00:00.0: BAR 1 [mem 0x40000000-0x7fffffff pref]: no
initial claim (no window)
     pci 0000:00:00.0: BAR 1 [mem size 0x40000000 pref]
     pci 0000:00:01.0: [1033:0035] type 00 class 0x0c0310 conventional
PCI endpoint
    -pci 0000:00:01.0: BAR 0 [mem 0x00000000-0x00000fff]: no initial
claim (no window)
     pci 0000:00:01.0: BAR 0 [mem size 0x00001000]
     pci 0000:00:01.0: supports D1 D2
     pci 0000:00:01.0: PME# supported from D0 D1 D2 D3hot
     pci 0000:00:02.0: [1033:00e0] type 00 class 0x0c0320 conventional
PCI endpoint
    -pci 0000:00:02.0: BAR 0 [mem 0x00000000-0x000000ff]: no initial
claim (no window)
     pci 0000:00:02.0: BAR 0 [mem size 0x00000100]
     pci 0000:00:02.0: supports D1 D2
     pci 0000:00:02.0: PME# supported from D0 D1 D2 D3hot
     PCI: bus0: Fast back to back transfers disabled
     pci 0000:00:01.0: BAR 0 [mem 0xee080000-0xee080fff]: assigned
     pci 0000:00:02.0: BAR 0 [mem 0xee081000-0xee0810ff]: assigned
     pci_bus 0000:00: resource 4 [mem 0xee080000-0xee08ffff]
     pci 0000:00:01.0: enabling device (0140 -> 0142)
     pci 0000:00:02.0: enabling device (0140 -> 0142)

I.e. the "no initial claim (no window)" messages introduced by commit
06b77d5647a4d6a7 are no longer seen.
The BARs still show "mem size <n>" instead of the "mem <start>-<end>"
before commit 06b77d5647a4d6a7, though.

This series has not impact on /proc/iomem, or on the output of
"lspci -v" (commit 06b77d5647a4d6a7 also had no impact here).
I.e. the part of /proc/iomem related to the first PCI/USB instance
still looks like:

    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 hope this matches your expectation.s

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds