vgaarb: Add support for setting the default video device (v2)

The default VGA device is a somewhat fluid concept on platforms with
multiple GPUs. Add support for setting it so switching code can update
things appropriately, and make sure that the sysfs code returns the right
device if it's changed.

v2: Updated to fix builds when __ARCH_HAS_VGA_DEFAULT_DEVICE is false.

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Acked-by: benh@kernel.crashing.org
Cc: airlied@redhat.com
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/vga/vgaarb.c

@@ -136,6 +136,11 @@ struct pci_dev *vga_default_device(void)
 {
 	return vga_default;
 }
+
+void vga_set_default_device(struct pci_dev *pdev)
+{
+	vga_default = pdev;
+}
 #endif
 
 static inline void vga_irq_set_state(struct vga_device *vgadev, bool state)
@@ -605,10 +610,12 @@ static bool vga_arbiter_del_pci_device(struct pci_dev *pdev)
 		goto bail;
 	}
 
+#ifndef __ARCH_HAS_VGA_DEFAULT_DEVICE
 	if (vga_default == pdev) {
 		pci_dev_put(vga_default);
 		vga_default = NULL;
 	}
+#endif
 
 	if (vgadev->decodes & (VGA_RSRC_LEGACY_IO | VGA_RSRC_LEGACY_MEM))
 		vga_decode_count--;