[PATCH V3] PCI: vmd: Fix secondary bus reset for Intel bridges

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From: Francisco Munoz <francisco.munoz.ruiz@xxxxxxxxxxxxxxx>

The reset was never applied in the current implementation because Intel
Bridges owned by VMD are parentless. Internally, pci_reset_bus() applies
a reset to the parent of the PCI device supplied as argument, but in this
case it failed because there wasn't a parent.

In more detail, this change allows the VMD driver to enumerate NVMe devices
in pass-through configurations when guest reboots are performed. Commit id
6aab5622296b ("PCI: vmd: Clean up domain before enumeration") attempted to
fix this, but later we discovered that the code inside pci_reset_bus() wasn’t
triggering secondary bus resets.  Therefore, we updated the parameters passed
to it, and now NVMe SSDs attached to VMD bridges are properly enumerated in
VT-d pass-through scenarios.

Signed-off-by: Francisco Munoz <francisco.munoz.ruiz@xxxxxxxxxxxxxxx>
Reviewed-by: Nirmal Patel <nirmal.patel@xxxxxxxxxxxxxxx>
Reviewed-by: Jonathan Derrick <jonathan.derrick@xxxxxxxxx>
---
V3:
    - Add WARN_ON
    - Include Jonathan as reviewer
    - Update commit message
V2:
    - Update commit message

 drivers/pci/controller/vmd.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
index e06e9f4fc50f..2406be6644f3 100644
--- a/drivers/pci/controller/vmd.c
+++ b/drivers/pci/controller/vmd.c
@@ -859,8 +859,17 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
 
 	pci_scan_child_bus(vmd->bus);
 	vmd_domain_reset(vmd);
-	list_for_each_entry(child, &vmd->bus->children, node)
-		pci_reset_bus(child->self);
+
+	list_for_each_entry(child, &vmd->bus->children, node) {
+		if (!list_empty(&child->devices)) {
+			ret = pci_reset_bus(list_first_entry(&child->devices,
+							     struct pci_dev,
+							     bus_list));
+			WARN_ON(ret);
+			break;
+		}
+	}
+
 	pci_assign_unassigned_bus_resources(vmd->bus);
 
 	/*
-- 
2.25.1




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