vgaarb: use bridges to control VGA routing where possible.

So in a lot of modern systems, a GPU will always be below a parent bridge that won't share with any other GPUs. This means VGA arbitration on those GPUs can be controlled by using the bridge routing instead of io/mem decodes.

The problem is locating which GPUs share which upstream bridges. This patch attempts to identify all the GPUs which can be controlled via bridges, and ones that can't. This patch endeavours to work out the bridge sharing semantics.

When disabling GPUs via a bridge, it doesn't do irq callbacks or touch the io/mem decodes for the gpu.

Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 14 insertions, 11 deletions

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 2472e7177b4b..a339237f4f96 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -2875,31 +2875,34 @@ static int pci_set_vga_state_arch(struct pci_dev *dev, bool decode,
  * @dev: the PCI device
  * @decode: true = enable decoding, false = disable decoding
  * @command_bits: PCI_COMMAND_IO and/or PCI_COMMAND_MEMORY
- * @change_bridge: traverse ancestors and change bridges
+ * @change_bridge_flags: traverse ancestors and change bridges
+ * CHANGE_BRIDGE_ONLY / CHANGE_BRIDGE
  */
 int pci_set_vga_state(struct pci_dev *dev, bool decode,
-                      unsigned int command_bits, bool change_bridge)
+                      unsigned int command_bits, u32 flags)
 {
         struct pci_bus *bus;
         struct pci_dev *bridge;
         u16 cmd;
         int rc;
 
-        WARN_ON(command_bits & ~(PCI_COMMAND_IO|PCI_COMMAND_MEMORY));
+        WARN_ON((flags & PCI_VGA_STATE_CHANGE_DECODES) & (command_bits & ~(PCI_COMMAND_IO|PCI_COMMAND_MEMORY)));
 
         /* ARCH specific VGA enables */
-        rc = pci_set_vga_state_arch(dev, decode, command_bits, change_bridge);
+        rc = pci_set_vga_state_arch(dev, decode, command_bits, flags);
         if (rc)
                 return rc;
 
-        pci_read_config_word(dev, PCI_COMMAND, &cmd);
-        if (decode == true)
-                cmd |= command_bits;
-        else
-                cmd &= ~command_bits;
-        pci_write_config_word(dev, PCI_COMMAND, cmd);
+        if (flags & PCI_VGA_STATE_CHANGE_DECODES) {
+                pci_read_config_word(dev, PCI_COMMAND, &cmd);
+                if (decode == true)
+                        cmd |= command_bits;
+                else
+                        cmd &= ~command_bits;
+                pci_write_config_word(dev, PCI_COMMAND, cmd);
+        }
 
-        if (change_bridge == false)
+        if (!(flags & PCI_VGA_STATE_CHANGE_BRIDGE))
                 return 0;
 
         bus = dev->bus;