[Qemu-devel] [PATCH] hw/pci-bridge: remove 16 PCIe devices limitation by making IO forwarding optional

[Marcel Apfelbaum <marcel@redhat.com>]

PCIe downstream ports (Root Ports and switches Downstream Ports) appear
to firmware as PCI-PCI bridges and a 4K IO space is allocated for them.
Because of the available IO space, maximum 16 PCI-PCI bridges can exist
per system.

However PCIe devices can work without IO, so add 'disable-io-forwarding'
property to bridges that makes the optional IOBASE/IO_LIMIT read-only
allowing the firmware to skip allocating IO space.

Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
---
 hw/pci/pci.c             | 21 +++++++++++++++------
 hw/pci/pci_bridge.c      | 25 +++++++++++++++++++++----
 include/hw/pci/pci_bus.h |  4 ++++
 3 files changed, 40 insertions(+), 10 deletions(-)

diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index 168b9cc..bda3391 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -707,13 +707,18 @@ static void pci_init_w1cmask(PCIDevice *dev)
 
 static void pci_init_mask_bridge(PCIDevice *d)
 {
+    bool io_forwarding_enabled = !(PCI_BRIDGE(d)->flags &
+                                   PCI_BRIDGE_FLAG_DISABLE_IO_FWD);
+
     /* PCI_PRIMARY_BUS, PCI_SECONDARY_BUS, PCI_SUBORDINATE_BUS and
        PCI_SEC_LETENCY_TIMER */
     memset(d->wmask + PCI_PRIMARY_BUS, 0xff, 4);
 
     /* base and limit */
-    d->wmask[PCI_IO_BASE] = PCI_IO_RANGE_MASK & 0xff;
-    d->wmask[PCI_IO_LIMIT] = PCI_IO_RANGE_MASK & 0xff;
+    if (io_forwarding_enabled) {
+        d->wmask[PCI_IO_BASE] = PCI_IO_RANGE_MASK & 0xff;
+        d->wmask[PCI_IO_LIMIT] = PCI_IO_RANGE_MASK & 0xff;
+    }
     pci_set_word(d->wmask + PCI_MEMORY_BASE,
                  PCI_MEMORY_RANGE_MASK & 0xffff);
     pci_set_word(d->wmask + PCI_MEMORY_LIMIT,
@@ -727,8 +732,10 @@ static void pci_init_mask_bridge(PCIDevice *d)
     memset(d->wmask + PCI_PREF_BASE_UPPER32, 0xff, 8);
 
     /* Supported memory and i/o types */
-    d->config[PCI_IO_BASE] |= PCI_IO_RANGE_TYPE_16;
-    d->config[PCI_IO_LIMIT] |= PCI_IO_RANGE_TYPE_16;
+    if (io_forwarding_enabled) {
+        d->config[PCI_IO_BASE] |= PCI_IO_RANGE_TYPE_16;
+        d->config[PCI_IO_LIMIT] |= PCI_IO_RANGE_TYPE_16;
+    }
     pci_word_test_and_set_mask(d->config + PCI_PREF_MEMORY_BASE,
                                PCI_PREF_RANGE_TYPE_64);
     pci_word_test_and_set_mask(d->config + PCI_PREF_MEMORY_LIMIT,
@@ -754,8 +761,10 @@ static void pci_init_mask_bridge(PCIDevice *d)
      * completeness. */
     pci_set_word(d->w1cmask + PCI_BRIDGE_CONTROL,
                  PCI_BRIDGE_CTL_DISCARD_STATUS);
-    d->cmask[PCI_IO_BASE] |= PCI_IO_RANGE_TYPE_MASK;
-    d->cmask[PCI_IO_LIMIT] |= PCI_IO_RANGE_TYPE_MASK;
+    if (io_forwarding_enabled) {
+        d->cmask[PCI_IO_BASE] |= PCI_IO_RANGE_TYPE_MASK;
+        d->cmask[PCI_IO_LIMIT] |= PCI_IO_RANGE_TYPE_MASK;
+    }
     pci_word_test_and_set_mask(d->cmask + PCI_PREF_MEMORY_BASE,
                                PCI_PREF_RANGE_TYPE_MASK);
     pci_word_test_and_set_mask(d->cmask + PCI_PREF_MEMORY_LIMIT,
diff --git a/hw/pci/pci_bridge.c b/hw/pci/pci_bridge.c
index 40c97b1..8b418dd 100644
--- a/hw/pci/pci_bridge.c
+++ b/hw/pci/pci_bridge.c
@@ -276,10 +276,13 @@ void pci_bridge_disable_base_limit(PCIDevice *dev)
 {
     uint8_t *conf = dev->config;
 
-    pci_byte_test_and_set_mask(conf + PCI_IO_BASE,
-                               PCI_IO_RANGE_MASK & 0xff);
-    pci_byte_test_and_clear_mask(conf + PCI_IO_LIMIT,
-                                 PCI_IO_RANGE_MASK & 0xff);
+    if (!(PCI_BRIDGE(dev)->flags & PCI_BRIDGE_FLAG_DISABLE_IO_FWD)) {
+        pci_byte_test_and_set_mask(conf + PCI_IO_BASE,
+                                   PCI_IO_RANGE_MASK & 0xff);
+        pci_byte_test_and_clear_mask(conf + PCI_IO_LIMIT,
+                                     PCI_IO_RANGE_MASK & 0xff);
+    }
+
     pci_word_test_and_set_mask(conf + PCI_MEMORY_BASE,
                                PCI_MEMORY_RANGE_MASK & 0xffff);
     pci_word_test_and_clear_mask(conf + PCI_MEMORY_LIMIT,
@@ -404,10 +407,24 @@ void pci_bridge_map_irq(PCIBridge *br, const char* bus_name,
     br->bus_name = bus_name;
 }
 
+static Property pci_bridge_properties[] = {
+    DEFINE_PROP_BIT("disable-io-forwarding", PCIBridge, flags,
+                    PCI_BRIDGE_FLAG_DISABLE_IO_FWD_BIT, false),
+    DEFINE_PROP_END_OF_LIST(),
+};
+
+static void pci_bridge_class_init(ObjectClass *klass, void *data)
+{
+    DeviceClass *dc = DEVICE_CLASS(klass);
+
+    dc->props = pci_bridge_properties;
+}
+
 static const TypeInfo pci_bridge_type_info = {
     .name = TYPE_PCI_BRIDGE,
     .parent = TYPE_PCI_DEVICE,
     .instance_size = sizeof(PCIBridge),
+    .class_init = pci_bridge_class_init,
     .abstract = true,
 };
 
diff --git a/include/hw/pci/pci_bus.h b/include/hw/pci/pci_bus.h
index 403fec6..1e02198 100644
--- a/include/hw/pci/pci_bus.h
+++ b/include/hw/pci/pci_bus.h
@@ -64,6 +64,9 @@ struct PCIBridgeWindows {
 #define TYPE_PCI_BRIDGE "base-pci-bridge"
 #define PCI_BRIDGE(obj) OBJECT_CHECK(PCIBridge, (obj), TYPE_PCI_BRIDGE)
 
+#define PCI_BRIDGE_FLAG_DISABLE_IO_FWD_BIT 0
+#define PCI_BRIDGE_FLAG_DISABLE_IO_FWD (1 << PCI_BRIDGE_FLAG_DISABLE_IO_FWD_BIT)
+
 struct PCIBridge {
     /*< private >*/
     PCIDevice parent_obj;
@@ -86,6 +89,7 @@ struct PCIBridge {
 
     pci_map_irq_fn map_irq;
     const char *bus_name;
+    uint32_t flags;
 };
 
 #endif /* QEMU_PCI_BUS_H */
-- 
2.1.0