linux-kernel - Re: [PATCH v2] PCI: acpiphp: Reassign resources on bridge if necessary

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Date:   Tue, 30 May 2023 12:12:44 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Igor Mammedov <imammedo@...hat.com>
Cc:     linux-kernel@...r.kernel.org, mst@...hat.com, rafael@...nel.org,
        lenb@...nel.org, bhelgaas@...gle.com, linux-acpi@...r.kernel.org,
        linux-pci@...r.kernel.org, mika.westerberg@...ux.intel.com
Subject: Re: [PATCH v2] PCI: acpiphp: Reassign resources on bridge if
 necessary

On Mon, Apr 24, 2023 at 09:15:57PM +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)

Ugh, I just noticed that we turned on PCI_COMMAND_MEMORY even though
BARs 0 and 1 haven't been assigned.  How did that happen?  It looks
like pci_enable_resources() checks for that, but there must be a hole
somewhere.

>    Unable to create vram_mapping
>    qxl: probe of 0000:01:00.0 failed with error -12