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>

4 files changed, 55 insertions, 2 deletions

diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index ed43111bce..a88160236e 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -674,6 +674,10 @@ static void pci_init_mask_bridge(PCIDevice *d)
 #define  PCI_BRIDGE_CTL_SEC_DISCARD	0x200	/* Secondary discard timer */
 #define  PCI_BRIDGE_CTL_DISCARD_STATUS	0x400	/* Discard timer status */
 #define  PCI_BRIDGE_CTL_DISCARD_SERR	0x800	/* Discard timer SERR# enable */
+/*
+ * TODO: Bridges default to 10-bit VGA decoding but we currently only
+ * implement 16-bit decoding (no alias support).
+ */
     pci_set_word(d->wmask + PCI_BRIDGE_CONTROL,
                  PCI_BRIDGE_CTL_PARITY |
                  PCI_BRIDGE_CTL_SERR |
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) |
diff --git a/hw/pci/pci_bus.h b/hw/pci/pci_bus.h
index f905b9e11e..aef559ae1f 100644
--- a/hw/pci/pci_bus.h
+++ b/hw/pci/pci_bus.h
@@ -47,6 +47,13 @@ struct PCIBridgeWindows {
     MemoryRegion alias_pref_mem;
     MemoryRegion alias_mem;
     MemoryRegion alias_io;
+    /*
+     * When bridge control VGA forwarding is enabled, bridges will
+     * provide positive decode on the PCI VGA defined I/O port and
+     * MMIO ranges.  When enabled forwarding is only qualified on the
+     * I/O and memory enable bits in the bridge command register.
+     */
+    MemoryRegion alias_vga[QEMU_PCI_VGA_NUM_REGIONS];
 };
 
 struct PCIBridge {
diff --git a/hw/pci/pcie_port.c b/hw/pci/pcie_port.c
index 33a6b0a08a..1be107b0c9 100644
--- a/hw/pci/pcie_port.c
+++ b/hw/pci/pcie_port.c
@@ -28,10 +28,12 @@ void pcie_port_init_reg(PCIDevice *d)
     pci_set_word(d->config + PCI_SEC_STATUS, 0);
 
     /* Unlike conventional pci bridge, some bits are hardwired to 0. */
+#define  PCI_BRIDGE_CTL_VGA_16BIT       0x10    /* VGA 16-bit decode */
     pci_set_word(d->wmask + PCI_BRIDGE_CONTROL,
                  PCI_BRIDGE_CTL_PARITY |
                  PCI_BRIDGE_CTL_ISA |
                  PCI_BRIDGE_CTL_VGA |
+                 PCI_BRIDGE_CTL_VGA_16BIT | /* Req, but no alias support yet */
                  PCI_BRIDGE_CTL_SERR |
                  PCI_BRIDGE_CTL_BUS_RESET);
 }