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Date:   Mon, 24 Apr 2023 21:26:11 +0200
From:   Igor Mammedov <imammedo@redhat.com>
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     linux-kernel@vger.kernel.org, rafael@kernel.org, lenb@kernel.org,
        bhelgaas@google.com, linux-acpi@vger.kernel.org,
        linux-pci@vger.kernel.org, imammedo@redhat.com
Subject: Re: [PATCH] pci: acpiphp: try to reassign resources on bridge if
 necessary
Message-ID: <20230424212611.6ec28e12@imammedo.users.ipa.redhat.com>
In-Reply-To: <20230418070640-mutt-send-email-mst@kernel.org>
References: <20230418085030.2154918-1-imammedo@redhat.com>
        <20230418070640-mutt-send-email-mst@kernel.org>
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On Tue, 18 Apr 2023 07:08:09 -0400
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Tue, Apr 18, 2023 at 10:50:30AM +0200, Igor Mammedov 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.
> > 
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>  
> 
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> 
> And I think:
> 
> Fixes: d66ecb7220a7 ("PCI / ACPI: Use boot-time resource allocation rules during hotplug")

Probably not, this commit basically added pcibios_resource_survey_bus() and
nothing else important. Looking through history it was always broken this way.

> 
> > ---
> > 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)
> >  				}
> >  			}
> >  		}
> > -		__pci_bus_assign_resources(bus, &add_list, NULL);
> > +		pci_assign_unassigned_bridge_resources(bus->self);
> >  	}
> >  
> >  	acpiphp_sanitize_bus(bus);
> > -- 
> > 2.39.1  
>