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Message-ID: <20230424205014.2c213437@imammedo.users.ipa.redhat.com>
Date: Mon, 24 Apr 2023 20:50:14 +0200
From: Igor Mammedov <imammedo@...hat.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
linux-kernel@...r.kernel.org, mst@...hat.com, lenb@...nel.org,
bhelgaas@...gle.com, linux-acpi@...r.kernel.org,
linux-pci@...r.kernel.org,
Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH] pci: acpiphp: try to reassign resources on bridge if
necessary
On Tue, 18 Apr 2023 11:31:14 -0500
Bjorn Helgaas <helgaas@...nel.org> wrote:
> [+cc Mika, who made previous changes in this area]
>
> On Tue, Apr 18, 2023 at 05:38:15PM +0200, Rafael J. Wysocki wrote:
> > On Tue, Apr 18, 2023 at 4:17 PM Igor Mammedov <imammedo@...hat.com> wrote:
> > > On Tue, 18 Apr 2023 14:55:29 +0200
> > > "Rafael J. Wysocki" <rafael@...nel.org> wrote:
> > > > On Tue, Apr 18, 2023 at 10:50 AM Igor Mammedov <imammedo@...hat.com> wrote:
> > > > >
> > > > > When using ACPI PCI hotplug, hotplugging a device with
> > > > > large BARs may fail if bridge windows programmed by
> > > > > firmware are not large enough.
> > > > >
> > > > > Reproducer:
> > > > > $ qemu-kvm -monitor stdio -M q35 -m 4G \
> > > > > -global ICH9-LPC.acpi-pci-hotplug-with-bridge-support=on \
> > > > > -device id=rp1,pcie-root-port,bus=pcie.0,chassis=4 \
> > > > > disk_image
> > > > >
> > > > > wait till linux guest boots, then hotplug device
> > > > > (qemu) device_add qxl,bus=rp1
> > > > >
> > > > > hotplug on guest side fails with:
> > > > > pci 0000:01:00.0: [1b36:0100] type 00 class 0x038000
> > > > > pci 0000:01:00.0: reg 0x10: [mem 0x00000000-0x03ffffff]
> > > > > pci 0000:01:00.0: reg 0x14: [mem 0x00000000-0x03ffffff]
> > > > > pci 0000:01:00.0: reg 0x18: [mem 0x00000000-0x00001fff]
> > > > > pci 0000:01:00.0: reg 0x1c: [io 0x0000-0x001f]
> > > > > pci 0000:01:00.0: BAR 0: no space for [mem size 0x04000000]
> > > > > pci 0000:01:00.0: BAR 0: failed to assign [mem size 0x04000000]
> > > > > pci 0000:01:00.0: BAR 1: no space for [mem size 0x04000000]
> > > > > pci 0000:01:00.0: BAR 1: failed to assign [mem size 0x04000000]
> > > > > pci 0000:01:00.0: BAR 2: assigned [mem 0xfe800000-0xfe801fff]
> > > > > pci 0000:01:00.0: BAR 3: assigned [io 0x1000-0x101f]
> > > > > qxl 0000:01:00.0: enabling device (0000 -> 0003)
> > > > > Unable to create vram_mapping
> > > > > qxl: probe of 0000:01:00.0 failed with error -12
> > > > >
> > > > > However when using native PCIe hotplug
> > > > > '-global ICH9-LPC.acpi-pci-hotplug-with-bridge-support=off'
> > > > > it works fine, since kernel attempts to reassign unused resources.
> > > > > Use the same machinery as native PCIe hotplug to (re)assign resources.
>
> Thanks for the nice reproducer and logs!
>
> > > > > Signed-off-by: Igor Mammedov <imammedo@...hat.com>
> > > >
> > > > Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > >
> > > > or please let me know if you want me to pick this up.
> > >
> > > It would be nice if you could pick it up.
> >
> > OK, I'll do that unless Bjorn tells me that he prefers to take it via
> > the PCI tree.
>
> It's OK with me if you pick this up, but please update the subject to
> use the style of previous commits, e.g.,
>
> PCI: acpiphp: Reassign resources on bridge if necessary
>
> Previous changes involving pci_assign_unassigned_bridge_resources() in
> enable_slot() (these are from Mika, so I cc'd him in case he wants to
> comment):
>
> 84c8b58ed3ad ("ACPI / hotplug / PCI: Don't scan bridges managed by native hotplug")
> 77adf9355304 ("ACPI / hotplug / PCI: Allocate resources directly under the non-hotplug bridge")
>
> > > > > ---
> > > > > tested in QEMU with Q35 machine on PCIE root port and also
> > > > > with nested conventional bridge attached to root port.
> > > > > ---
> > > > > drivers/pci/hotplug/acpiphp_glue.c | 2 +-
> > > > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/pci/hotplug/acpiphp_glue.c b/drivers/pci/hotplug/acpiphp_glue.c
> > > > > index 5b1f271c6034..9aebde28a92f 100644
> > > > > --- a/drivers/pci/hotplug/acpiphp_glue.c
> > > > > +++ b/drivers/pci/hotplug/acpiphp_glue.c
> > > > > @@ -517,7 +517,7 @@ static void enable_slot(struct acpiphp_slot *slot, bool bridge)
>
> Previous context:
>
> __pci_bus_size_bridges(dev->subordinate,
> &add_list);
>
> > > > > }
> > > > > }
> > > > > }
> > > > > - __pci_bus_assign_resources(bus, &add_list, NULL);
> > > > > + pci_assign_unassigned_bridge_resources(bus->self);
>
> "add_list" is now used only for __pci_bus_size_bridges(), which
> *looks* unnecessary unless there's some obscure side-effect of that
> path when that parameter is non-NULL.
>
> If "add_list" is unnecessary, you would probably use
> pci_bus_size_bridges() above instead of __pci_bus_size_bridges().
pci_assign_unassigned_bridge_resources() calls __pci_bus_size_bridges()
so original one is not needed anymore, in addition it might leak entries
added to add_list.
I'll remove __pci_bus_size_bridges() and respin patch (incl. updated subject)
> After this patch, we have:
>
> if (bridge && bus->self && hotplug_is_native(bus->self)) {
> for_each_pci_bridge(dev, bus)
> acpiphp_native_scan_bridge(dev);
> } else {
> ...
> pci_assign_unassigned_bridge_resources(bus->self);
> }
>
> We do not do pci_assign_unassigned_bridge_resources() in the "then"
> part of the "if". Per the comment, that case may be used for adding
> Thunderbolt controllers. Is there a reason we do not want
> pci_assign_unassigned_bridge_resources() in that path,
> or should it be
> in both cases?
acpiphp_native_scan_bridge() looks very similar to 'else'
branch modulo skip native hp bridge condition.
Otherwise both branches look similar,
but I don't have means to test that usecase,
so I'd avoid touching something nobody complains about.
>
> > > > > }
> > > > >
> > > > > acpiphp_sanitize_bus(bus);
>
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