linux-kernel - Re: [PATCH] pci: acpiphp: try to reassign resources on bridge if necessary

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Date:   Tue, 18 Apr 2023 07:08:09 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Igor Mammedov <imammedo@...hat.com>
Cc:     linux-kernel@...r.kernel.org, rafael@...nel.org, lenb@...nel.org,
        bhelgaas@...gle.com, linux-acpi@...r.kernel.org,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH] pci: acpiphp: try to reassign resources on bridge if
 necessary

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@...hat.com>

Acked-by: Michael S. Tsirkin <mst@...hat.com>

And I think:

Fixes: d66ecb7220a7 ("PCI / ACPI: Use boot-time resource allocation rules during hotplug")


> ---
> 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