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From:   Igor Mammedov <imammedo@redhat.com>
To:     linux-kernel@vger.kernel.org
Cc:     mst@redhat.com, rafael@kernel.org, lenb@kernel.org,
        bhelgaas@google.com, linux-acpi@vger.kernel.org,
        linux-pci@vger.kernel.org
Subject: [PATCH] pci: acpiphp: try to reassign resources on bridge if necessary
Date:   Tue, 18 Apr 2023 10:50:30 +0200
Message-Id: <20230418085030.2154918-1-imammedo@redhat.com>
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Precedence: bulk

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>
---
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