[RFC PATCH v3 16/31] hw/pci: Plumb _UID through host bridges

[Ben Widawsky]

Currently, QEMU makes _UID equivalent to the bus number (_BBN). While
there is nothing wrong with doing it this way, CXL spec has a heavy
reliance on _UID to identify host bridges and there is no link to the
bus number. Having a distinct UID solves two problems. The first is it
gets us around the limitation of 256 (current max bus number). The
second is it allows us to replicate hardware configurations where bus
number and uid aren't equivalent. The latter has benefits for our
development and debugging using QEMU.

The other way to do this would be to implement the expanded bus
numbering, but having an explicit uid makes more sense when trying to
replicate real hardware configurations.

The QEMU commandline to utilize this would be:
  -device pxb-cxl,id=cxl.0,bus="pcie.0",bus_nr=1,uid=x

Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>

--

I'm guessing this patch will be somewhat controversial. For early CXL
work, this can be dropped without too much heartache.
---
 hw/i386/acpi-build.c                |  3 ++-
 hw/pci-bridge/pci_expander_bridge.c | 19 +++++++++++++++++++
 hw/pci/pci.c                        | 11 +++++++++++
 include/hw/pci/pci.h                |  1 +
 include/hw/pci/pci_bus.h            |  1 +
 5 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
index cf6eb54c22..145a503e92 100644
--- a/hw/i386/acpi-build.c
+++ b/hw/i386/acpi-build.c
@@ -1343,6 +1343,7 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
         QLIST_FOREACH(bus, &bus->child, sibling) {
             uint8_t bus_num = pci_bus_num(bus);
             uint8_t numa_node = pci_bus_numa_node(bus);
+            int32_t uid = pci_bus_uid(bus);
 
             /* look only for expander root buses */
             if (!pci_bus_is_root(bus)) {
@@ -1356,7 +1357,7 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
             scope = aml_scope("\\_SB");
             dev = aml_device("PC%.02X", bus_num);
             aml_append(dev, aml_name_decl("_BBN", aml_int(bus_num)));
-            init_pci_acpi(dev, bus_num, pci_bus_is_express(bus) ? PCIE : PCI);
+            init_pci_acpi(dev, uid, pci_bus_is_express(bus) ? PCIE : PCI);
 
             if (numa_node != NUMA_NODE_UNASSIGNED) {
                 aml_append(dev, aml_name_decl("_PXM", aml_int(numa_node)));
diff --git a/hw/pci-bridge/pci_expander_bridge.c 
b/hw/pci-bridge/pci_expander_bridge.c
index b42592e1ff..5021b60435 100644
--- a/hw/pci-bridge/pci_expander_bridge.c
+++ b/hw/pci-bridge/pci_expander_bridge.c
@@ -67,6 +67,7 @@ struct PXBDev {
 
     uint8_t bus_nr;
     uint16_t numa_node;
+    int32_t uid;
 };
 
 static PXBDev *convert_to_pxb(PCIDevice *dev)
@@ -98,12 +99,20 @@ static uint16_t pxb_bus_numa_node(PCIBus *bus)
     return pxb->numa_node;
 }
 
+static int32_t pxb_bus_uid(PCIBus *bus)
+{
+    PXBDev *pxb = convert_to_pxb(bus->parent_dev);
+
+    return pxb->uid;
+}
+
 static void pxb_bus_class_init(ObjectClass *class, void *data)
 {
     PCIBusClass *pbc = PCI_BUS_CLASS(class);
 
     pbc->bus_num = pxb_bus_num;
     pbc->numa_node = pxb_bus_numa_node;
+    pbc->uid = pxb_bus_uid;
 }
 
 static const TypeInfo pxb_bus_info = {
@@ -329,6 +338,7 @@ static Property pxb_dev_properties[] = {
     /* Note: 0 is not a legal PXB bus number. */
     DEFINE_PROP_UINT8("bus_nr", PXBDev, bus_nr, 0),
     DEFINE_PROP_UINT16("numa_node", PXBDev, numa_node, NUMA_NODE_UNASSIGNED),
+    DEFINE_PROP_INT32("uid", PXBDev, uid, -1),
     DEFINE_PROP_END_OF_LIST(),
 };
 
@@ -400,12 +410,21 @@ static const TypeInfo pxb_pcie_dev_info = {
 
 static void pxb_cxl_dev_realize(PCIDevice *dev, Error **errp)
 {
+    PXBDev *pxb = convert_to_pxb(dev);
+
     /* A CXL PXB's parent bus is still PCIe */
     if (!pci_bus_is_express(pci_get_bus(dev))) {
         error_setg(errp, "pxb-cxl devices cannot reside on a PCI bus");
         return;
     }
 
+    if (pxb->uid < 0) {
+        error_setg(errp, "pxb-cxl devices must have a valid uid 
(0-2147483647)");
+        return;
+    }
+
+    /* FIXME: Check that uid doesn't collide with UIDs of other host bridges */
+
     pxb_dev_realize_common(dev, CXL, errp);
 }
 
diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index adbe8aa260..bf019d91a0 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -170,6 +170,11 @@ static uint16_t pcibus_numa_node(PCIBus *bus)
     return NUMA_NODE_UNASSIGNED;
 }
 
+static int32_t pcibus_uid(PCIBus *bus)
+{
+    return -1;
+}
+
 static void pci_bus_class_init(ObjectClass *klass, void *data)
 {
     BusClass *k = BUS_CLASS(klass);
@@ -184,6 +189,7 @@ static void pci_bus_class_init(ObjectClass *klass, void 
*data)
 
     pbc->bus_num = pcibus_num;
     pbc->numa_node = pcibus_numa_node;
+    pbc->uid = pcibus_uid;
 }
 
 static const TypeInfo pci_bus_info = {
@@ -530,6 +536,11 @@ int pci_bus_numa_node(PCIBus *bus)
     return PCI_BUS_GET_CLASS(bus)->numa_node(bus);
 }
 
+int pci_bus_uid(PCIBus *bus)
+{
+    return PCI_BUS_GET_CLASS(bus)->uid(bus);
+}
+
 static int get_pci_config_device(QEMUFile *f, void *pv, size_t size,
                                  const VMStateField *field)
 {
diff --git a/include/hw/pci/pci.h b/include/hw/pci/pci.h
index bde3697bee..a46de48ccd 100644
--- a/include/hw/pci/pci.h
+++ b/include/hw/pci/pci.h
@@ -463,6 +463,7 @@ static inline int pci_dev_bus_num(const PCIDevice *dev)
 }
 
 int pci_bus_numa_node(PCIBus *bus);
+int pci_bus_uid(PCIBus *bus);
 void pci_for_each_device(PCIBus *bus, int bus_num,
                          void (*fn)(PCIBus *bus, PCIDevice *d, void *opaque),
                          void *opaque);
diff --git a/include/hw/pci/pci_bus.h b/include/hw/pci/pci_bus.h
index eb94e7e85c..3c9fbc55bb 100644
--- a/include/hw/pci/pci_bus.h
+++ b/include/hw/pci/pci_bus.h
@@ -17,6 +17,7 @@ struct PCIBusClass {
 
     int (*bus_num)(PCIBus *bus);
     uint16_t (*numa_node)(PCIBus *bus);
+    int32_t (*uid)(PCIBus *bus);
 };
 
 enum PCIBusFlags {
-- 
2.30.0