PCI: Add support for multiple DMA aliases

Solve IOMMU support issues with PCIe non-transparent bridges that use
Requester ID look-up tables (RID-LUT), e.g., the PEX8733.

The NTB connects devices in two independent PCI domains.  Devices separated
by the NTB are not able to discover each other.  A PCI packet being
forwared from one domain to another has to have its RID modified so it
appears on correct bus and completions are forwarded back to the original
domain through the NTB.  The RID is translated using a preprogrammed table
(LUT) and the PCI packet propagates upstream away from the NTB.  If the
destination system has IOMMU enabled, the packet will be discarded because
the new RID is unknown to the IOMMU.  Adding a DMA alias for the new RID
allows IOMMU to properly recognize the packet.

Each device behind the NTB has a unique RID assigned in the RID-LUT.  The
current DMA alias implementation supports only a single alias, so it's not
possible to support mutiple devices behind the NTB when IOMMU is enabled.

Enable all possible aliases on a given bus (256) that are stored in a
bitset.  Alias devfn is directly translated to a bit number.  The bitset is
not allocated for devices that have no need for DMA aliases.

More details can be found in the following article:
http://www.plxtech.com/files/pdf/technical/expresslane/RTC_Enabling%20MulitHostSystemDesigns.pdf

Signed-off-by: Jacek Lawrynowicz <jacek.lawrynowicz@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: David Woodhouse <David.Woodhouse@intel.com>
Acked-by: Joerg Roedel <jroedel@suse.de>

1 files changed, 17 insertions, 2 deletions

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index c82ebd0f6982..0b90c2186f1c 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4588,12 +4588,27 @@ int pci_set_vga_state(struct pci_dev *dev, bool decode,
  */
 void pci_add_dma_alias(struct pci_dev *dev, u8 devfn)
 {
-        dev->dma_alias_devfn = devfn;
-        dev->dev_flags |= PCI_DEV_FLAGS_DMA_ALIAS_DEVFN;
+        if (!dev->dma_alias_mask)
+                dev->dma_alias_mask = kcalloc(BITS_TO_LONGS(U8_MAX),
+                                              sizeof(long), GFP_KERNEL);
+        if (!dev->dma_alias_mask) {
+                dev_warn(&dev->dev, "Unable to allocate DMA alias mask\n");
+                return;
+        }
+
+        set_bit(devfn, dev->dma_alias_mask);
         dev_info(&dev->dev, "Enabling fixed DMA alias to %02x.%d\n",
                  PCI_SLOT(devfn), PCI_FUNC(devfn));
 }
 
+bool pci_devs_are_dma_aliases(struct pci_dev *dev1, struct pci_dev *dev2)
+{
+        return (dev1->dma_alias_mask &&
+                test_bit(dev2->devfn, dev1->dma_alias_mask)) ||
+               (dev2->dma_alias_mask &&
+                test_bit(dev1->devfn, dev2->dma_alias_mask));
+}
+
 bool pci_device_is_present(struct pci_dev *pdev)
 {
         u32 v;