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Date:   Mon, 22 May 2023 16:51:41 -0500
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Igor Mammedov <imammedo@redhat.com>
Cc:     linux-kernel@vger.kernel.org, mst@redhat.com, rafael@kernel.org,
        lenb@kernel.org, bhelgaas@google.com, linux-acpi@vger.kernel.org,
        linux-pci@vger.kernel.org, mika.westerberg@linux.intel.com
Subject: Re: [PATCH v2] PCI: acpiphp: Reassign resources on bridge if
 necessary
Message-ID: <ZGvj7aqaY3InNqun@bhelgaas>
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In-Reply-To: <20230424191557.2464760-1-imammedo@redhat.com>
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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)
>    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>

Tentatively applied to pci/hotplug for v6.5.

Tentative only because I'm hoping for your ack or review, Rafael (I
see you acked v1, but this one is a little different).

And I think you'd like a stable tag, Michael?  I'm happy to add one,
but wasn't sure if you wanted a separate ack for that.

> ---
> tested in QEMU with Q35 machine on PCIE root port and also
> with nested conventional bridge attached to root port.
> 
> v2:
>   * fixup subject to match expected style
>   * drop no longer needed __pci_bus_size_bridges() to avoid
>     memory leak (Bjorn Helgaas <helgaas@kernel.org>)
> ---
>  drivers/pci/hotplug/acpiphp_glue.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/drivers/pci/hotplug/acpiphp_glue.c b/drivers/pci/hotplug/acpiphp_glue.c
> index 5b1f271c6034..328d1e416014 100644
> --- a/drivers/pci/hotplug/acpiphp_glue.c
> +++ b/drivers/pci/hotplug/acpiphp_glue.c
> @@ -498,7 +498,6 @@ static void enable_slot(struct acpiphp_slot *slot, bool bridge)
>  				acpiphp_native_scan_bridge(dev);
>  		}
>  	} else {
> -		LIST_HEAD(add_list);
>  		int max, pass;
>  
>  		acpiphp_rescan_slot(slot);
> @@ -512,12 +511,10 @@ static void enable_slot(struct acpiphp_slot *slot, bool bridge)
>  				if (pass && dev->subordinate) {
>  					check_hotplug_bridge(slot, dev);
>  					pcibios_resource_survey_bus(dev->subordinate);
> -					__pci_bus_size_bridges(dev->subordinate,
> -							       &add_list);
>  				}
>  			}
>  		}
> -		__pci_bus_assign_resources(bus, &add_list, NULL);
> +		pci_assign_unassigned_bridge_resources(bus->self);
>  	}
>  
>  	acpiphp_sanitize_bus(bus);
> -- 
> 2.39.1
>