[PATCH v4] PCI: vmd: Clean up domain before enumeration

[Nirmal Patel <nirmal.patel@xxxxxxxxxxxxxxx>]

During VT-d pass-through, the VMD driver occasionally fails to
enumerate underlying NVMe devices when repetitive reboots are
performed in the guest OS. The issue can be resolved by resetting
VMD root ports for proper enumeration and triggering secondary bus
reset which will also propagate reset through downstream bridges.

Signed-off-by: Nirmal Patel <nirmal.patel@xxxxxxxxxxxxxxx>
Reviewed-by: Jon Derrick <jonathan.derrick@xxxxxxxxx>
---
v3->v4: Using pci_reset_bus function for secondary bus reset instead of
        manually triggering secondary bus reset, addressing review
        comments of v3.
v2->v3: Combining two functions into one, Remove redundant definations
        and Formatting fixes

 drivers/pci/controller/vmd.c | 37 ++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
index a5987e52700e..79f8b86ee45b 100644
--- a/drivers/pci/controller/vmd.c
+++ b/drivers/pci/controller/vmd.c
@@ -498,6 +498,40 @@ static inline void vmd_acpi_begin(void) { }
 static inline void vmd_acpi_end(void) { }
 #endif /* CONFIG_ACPI */
 
+static void vmd_domain_reset(struct vmd_dev *vmd)
+{
+	u16 bus, max_buses = resource_size(&vmd->resources[0]);
+	u8 dev, functions, fn, hdr_type;
+	char __iomem *base;
+
+	for (bus = 0; bus < max_buses; bus++) {
+		for (dev = 0; dev < 32; dev++) {
+			base = vmd->cfgbar + PCIE_ECAM_OFFSET(bus,
+						PCI_DEVFN(dev, 0), 0);
+
+			hdr_type = readb(base + PCI_HEADER_TYPE) &
+					 PCI_HEADER_TYPE_MASK;
+
+			functions = !!(hdr_type & 0x80) ? 8 : 1;
+			for (fn = 0; fn < functions; fn++) {
+				base = vmd->cfgbar + PCIE_ECAM_OFFSET(bus,
+						PCI_DEVFN(dev, fn), 0);
+
+				hdr_type = readb(base + PCI_HEADER_TYPE) &
+						PCI_HEADER_TYPE_MASK;
+
+				if (hdr_type != PCI_HEADER_TYPE_BRIDGE ||
+				    (readw(base + PCI_CLASS_DEVICE) !=
+				     PCI_CLASS_BRIDGE_PCI))
+					continue;
+
+				memset_io(base + PCI_IO_BASE, 0,
+					  PCI_ROM_ADDRESS1 - PCI_IO_BASE);
+			}
+		}
+	}
+}
+
 static void vmd_attach_resources(struct vmd_dev *vmd)
 {
 	vmd->dev->resource[VMD_MEMBAR1].child = &vmd->resources[1];
@@ -801,6 +835,9 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
 	vmd_acpi_begin();
 
 	pci_scan_child_bus(vmd->bus);
+	vmd_domain_reset(vmd);
+	list_for_each_entry(child, &vmd->bus->children, node)
+		pci_reset_bus(child->self);
 	pci_assign_unassigned_bus_resources(vmd->bus);
 
 	/*
-- 
2.27.0