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

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Ilpo,

On Tue, 21 Oct 2025 at 13:54, Ilpo Järvinen
<ilpo.jarvinen@linux.intel.com> wrote:
> On Tue, 21 Oct 2025, Geert Uytterhoeven wrote:
> > On Mon, 20 Oct 2025 at 18:20, Ilpo Järvinen
> > <ilpo.jarvinen@linux.intel.com> wrote:
> > > On Mon, 20 Oct 2025, Geert Uytterhoeven wrote:
> > > > On Fri, 10 Oct 2025 at 16:42, Ilpo Järvinen
> > > > <ilpo.jarvinen@linux.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).

Thanks, all done:

    $ git cherry -v --abbrev=1 v6.18-rc2^
    + 211ddde0 Linux 6.18-rc2
    + 3fdaf2 PCI: Setup bridge resources earlier
    + 5be02e5 PCI: Resources outside their window must set IORESOURCE_UNSET
    + adf6f11 PCI: rcar-gen2: Add BAR0 into host bridge resources
    + eecb500 PCI: Refactor host bridge window coalescing loop to use prev
    + 60470b3 PCI: Do not coalesce host bridge resource structs in place
    + afe3ec resource, kunit: add test case for resource_coalesce()
    + 487c98 Use dev_info() in drivers/pci/probe.c:__pci_read_base()
IORESOURCE_UNSET path

Compared to v6.18-rc2, dmesg changed (for the first PCI/USB instance)
like:

     pci-rcar-gen2 ee090000.pci: host bridge /soc/pci@ee090000 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_bus 0000:00: root bus resource [mem 0xee090000-0xee090bff]
     pci 0000:00:00.0: [1033:0000] type 00 class 0x060000 conventional
PCI endpoint
     pci 0000:00:00.0: BAR 0 [mem 0xee090800-0xee090bff]
    -pci 0000:00:00.0: BAR 1 [mem 0x40000000-0x7fffffff pref]
    +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]
    +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]
    +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_bus 0000:00: resource 5 [mem 0xee090000-0xee090bff]
     pci 0000:00:01.0: enabling device (0140 -> 0142)
     pci 0000:00:02.0: enabling device (0140 -> 0142)

> 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@ee090000
>       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@ee090000

Compared to v6.18-rc2, the output of "lspci -v" or "cat /proc/iomem"
did not change.  Hence for the two PCI/USB instances:

    ee080000-ee08ffff : pci@ee090000
      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@ee090000
    ee0c0000-ee0cffff : pci@ee0d0000
      ee0c0000-ee0c0fff : 0001:01:01.0
        ee0c0000-ee0c0fff : ohci_hcd
      ee0c1000-ee0c10ff : 0001:01:02.0
        ee0c1000-ee0c10ff : ehci_hcd
    ee0d0000-ee0d0bff : ee0d0000.pci pci@ee0d0000

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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