PCI: Add arch_can_pci_mmap_io() on architectures which can mmap() I/O space

This is relatively esoteric, and knowing that we don't have it makes life
easier in some cases rather than just an eventual -EINVAL from
pci_mmap_page_range().

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
diff --git a/drivers/pci/proc.c b/drivers/pci/proc.c
index a2aa58a..45e5cf7 100644
--- a/drivers/pci/proc.c
+++ b/drivers/pci/proc.c
@@ -202,6 +202,8 @@
 
 #ifdef HAVE_PCI_MMAP
 	case PCIIOC_MMAP_IS_IO:
+		if (!arch_can_pci_mmap_io())
+			return -EINVAL;
 		fpriv->mmap_state = pci_mmap_io;
 		break;
 
@@ -232,15 +234,16 @@
 {
 	struct pci_dev *dev = PDE_DATA(file_inode(file));
 	struct pci_filp_private *fpriv = file->private_data;
-	int i, ret, write_combine = 0, res_bit;
+	int i, ret, write_combine = 0, res_bit = IORESOURCE_MEM;
 
 	if (!capable(CAP_SYS_RAWIO))
 		return -EPERM;
 
-	if (fpriv->mmap_state == pci_mmap_io)
+	if (fpriv->mmap_state == pci_mmap_io) {
+		if (!arch_can_pci_mmap_io())
+			return -EINVAL;
 		res_bit = IORESOURCE_IO;
-	else
-		res_bit = IORESOURCE_MEM;
+	}
 
 	/* Make sure the caller is mapping a real resource for this device */
 	for (i = 0; i < PCI_ROM_RESOURCE; i++) {