When Linux runs as a guest VM in Hyper-V and Hyper-V adds the virtual
PCI bus to the guest, Hyper-V always provides unique PCI domain.

commit 4a9b0933bdfc ("PCI: hv: Use device serial number as PCI domain")
overrode unique domain with the serial number of the first device added
to the virtual PCI bus. The reason for that patch is to have a consistent
and short name for the device. But commit 4a9b0933bdfc ("PCI: hv: Use
device serial number as PCI domain") will not guarantee unique domain id.
For example, if the serial number of the device is 0 and there exists a
PCI bus with domain 0 already, this will cause the PCI bus registration
with kernel fails.

commit 4a9b0933bdfc ("PCI: hv: Use device serial number as PCI
domain") need to be reverted.

Revert commit 4a9b0933bdfc ("PCI: hv: Use device serial number as PCI
domain") so we can reliably support multiple devices being assigned to
a guest.

Fixes: 4a9b0933bdfc ("PCI: hv: Use device serial number as PCI domain")
Signed-off-by: Sridhar Pitchai <sridhar.pitc...@microsoft.com>
Cc: sta...@vger.kernel.org

---
Changes in v6:
* fix the commit comment. [Lorenzo Pieralisi, Bjorn Helgaas]
---
 drivers/pci/host/pci-hyperv.c | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/drivers/pci/host/pci-hyperv.c b/drivers/pci/host/pci-hyperv.c
index 2faf38eab785..ac67e56e451a 100644
--- a/drivers/pci/host/pci-hyperv.c
+++ b/drivers/pci/host/pci-hyperv.c
@@ -1518,17 +1518,6 @@ static struct hv_pci_dev *new_pcichild_device(struct 
hv_pcibus_device *hbus,
        get_pcichild(hpdev, hv_pcidev_ref_childlist);
        spin_lock_irqsave(&hbus->device_list_lock, flags);
 
-       /*
-        * When a device is being added to the bus, we set the PCI domain
-        * number to be the device serial number, which is non-zero and
-        * unique on the same VM.  The serial numbers start with 1, and
-        * increase by 1 for each device.  So device names including this
-        * can have shorter names than based on the bus instance UUID.
-        * Only the first device serial number is used for domain, so the
-        * domain number will not change after the first device is added.
-        */
-       if (list_empty(&hbus->children))
-               hbus->sysdata.domain = desc->ser;
        list_add_tail(&hpdev->list_entry, &hbus->children);
        spin_unlock_irqrestore(&hbus->device_list_lock, flags);
        return hpdev;
-- 
2.14.1

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