pci: Teach PCI Bridges about VGA routing

Each PCI Bridge has a set of implied VGA regions that are enabled when
the VGA bit is set in the bridge control register.  This allows VGA
devices behind bridges.  Unfortunately with VGA Enable, which we
formerly allowed but didn't back, comes along some required VGA
baggage.  VGA Palette Snooping is required, along with VGA 16-bit
decoding.  We don't yet have support for palette snooping.
We also don't have support for 10-bit VGA aliases, the default mode, but
we enable the register, even on root ports, to avoid confusing guests.
Fortunately there's likely nothing from this century that requires these
features, so the missing bits are noted with TODOs.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 42 insertions, 2 deletions

diff --git a/hw/pci/pci_bridge.c b/hw/pci/pci_bridge.c
index 995842a72d..edb8c8d9c9 100644
--- a/hw/pci/pci_bridge.c
+++ b/hw/pci/pci_bridge.c
@@ -151,6 +151,28 @@ static void pci_bridge_init_alias(PCIBridge *bridge, MemoryRegion *alias,
     memory_region_add_subregion_overlap(parent_space, base, alias, 1);
 }
 
+static void pci_bridge_init_vga_aliases(PCIBridge *br, PCIBus *parent,
+                                        MemoryRegion *alias_vga)
+{
+    uint16_t brctl = pci_get_word(br->dev.config + PCI_BRIDGE_CONTROL);
+
+    memory_region_init_alias(&alias_vga[QEMU_PCI_VGA_IO_LO],
+                             "pci_bridge_vga_io_lo", &br->address_space_io,
+                             QEMU_PCI_VGA_IO_LO_BASE, QEMU_PCI_VGA_IO_LO_SIZE);
+    memory_region_init_alias(&alias_vga[QEMU_PCI_VGA_IO_HI],
+                             "pci_bridge_vga_io_hi", &br->address_space_io,
+                             QEMU_PCI_VGA_IO_HI_BASE, QEMU_PCI_VGA_IO_HI_SIZE);
+    memory_region_init_alias(&alias_vga[QEMU_PCI_VGA_MEM],
+                             "pci_bridge_vga_mem", &br->address_space_mem,
+                             QEMU_PCI_VGA_MEM_BASE, QEMU_PCI_VGA_MEM_SIZE);
+
+    if (brctl & PCI_BRIDGE_CTL_VGA) {
+        pci_register_vga(&br->dev, &alias_vga[QEMU_PCI_VGA_MEM],
+                         &alias_vga[QEMU_PCI_VGA_IO_LO],
+                         &alias_vga[QEMU_PCI_VGA_IO_HI]);
+    }
+}
+
 static PCIBridgeWindows *pci_bridge_region_init(PCIBridge *br)
 {
     PCIBus *parent = br->dev.bus;
@@ -175,7 +197,8 @@ static PCIBridgeWindows *pci_bridge_region_init(PCIBridge *br)
                           &br->address_space_io,
                           parent->address_space_io,
                           cmd & PCI_COMMAND_IO);
-   /* TODO: optinal VGA and VGA palette snooping support. */
+
+    pci_bridge_init_vga_aliases(br, parent, w->alias_vga);
 
     return w;
 }
@@ -187,6 +210,7 @@ static void pci_bridge_region_del(PCIBridge *br, PCIBridgeWindows *w)
     memory_region_del_subregion(parent->address_space_io, &w->alias_io);
     memory_region_del_subregion(parent->address_space_mem, &w->alias_mem);
     memory_region_del_subregion(parent->address_space_mem, &w->alias_pref_mem);
+    pci_unregister_vga(&br->dev);
 }
 
 static void pci_bridge_region_cleanup(PCIBridge *br, PCIBridgeWindows *w)
@@ -194,6 +218,9 @@ static void pci_bridge_region_cleanup(PCIBridge *br, PCIBridgeWindows *w)
     memory_region_destroy(&w->alias_io);
     memory_region_destroy(&w->alias_mem);
     memory_region_destroy(&w->alias_pref_mem);
+    memory_region_destroy(&w->alias_vga[QEMU_PCI_VGA_IO_LO]);
+    memory_region_destroy(&w->alias_vga[QEMU_PCI_VGA_IO_HI]);
+    memory_region_destroy(&w->alias_vga[QEMU_PCI_VGA_MEM]);
     g_free(w);
 }
 
@@ -227,7 +254,10 @@ void pci_bridge_write_config(PCIDevice *d,
 
         /* memory base/limit, prefetchable base/limit and
            io base/limit upper 16 */
-        ranges_overlap(address, len, PCI_MEMORY_BASE, 20)) {
+        ranges_overlap(address, len, PCI_MEMORY_BASE, 20) ||
+
+        /* vga enable */
+        ranges_overlap(address, len, PCI_BRIDGE_CONTROL, 2)) {
         pci_bridge_update_mappings(s);
     }
 
@@ -306,6 +336,16 @@ int pci_bridge_initfn(PCIDevice *dev)
 
     pci_word_test_and_set_mask(dev->config + PCI_STATUS,
                                PCI_STATUS_66MHZ | PCI_STATUS_FAST_BACK);
+
+    /*
+     * TODO: We implement VGA Enable in the Bridge Control Register
+     * therefore per the PCI to PCI bridge spec we must also implement
+     * VGA Palette Snooping.  When done, set this bit writable:
+     *
+     * pci_word_test_and_set_mask(dev->wmask + PCI_COMMAND,
+     *                            PCI_COMMAND_VGA_PALETTE);
+     */
+
     pci_config_set_class(dev->config, PCI_CLASS_BRIDGE_PCI);
     dev->config[PCI_HEADER_TYPE] =
         (dev->config[PCI_HEADER_TYPE] & PCI_HEADER_TYPE_MULTI_FUNCTION) |