PCI: add pci_request_acs

Commit ae21ee65e8bc228416bbcc8a1da01c56a847a60c "PCI: acs p2p upsteram
forwarding enabling" doesn't actually enable ACS.

Add a function to pci core to allow an IOMMU to request that ACS
be enabled.  The existing mechanism of using iommu_found() in the pci
core to know when ACS should be enabled doesn't actually work due to
initialization order;  iommu has only been detected not initialized.

Have Intel and AMD IOMMUs request ACS, and Xen does as well during early
init of dom0.

Cc: Allen Kay <allen.m.kay@intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 6af212c509c5..cd9b375f49d5 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1550,6 +1550,16 @@ void pci_enable_ari(struct pci_dev *dev)
         bridge->ari_enabled = 1;
 }
 
+static int pci_acs_enable;
+
+/**
+ * pci_request_acs - ask for ACS to be enabled if supported
+ */
+void pci_request_acs(void)
+{
+        pci_acs_enable = 1;
+}
+
 /**
  * pci_enable_acs - enable ACS if hardware support it
  * @dev: the PCI device
@@ -1560,6 +1570,9 @@ void pci_enable_acs(struct pci_dev *dev)
         u16 cap;
         u16 ctrl;
 
+        if (!pci_acs_enable)
+                return;
+
         if (!pci_is_pcie(dev))
                 return;