[RFC v5 6/7] PCI: Add a new bit to pci_bus_flags to indicate interrupt remapping

[Yongji Xie]

I'm trying to find a proper way to indicate
the capability of interrupt remapping on PPC64
because we need this to determine whether it is
safe to mmap MSI-X table in VFIO driver.

There is a existing flag for this in the IOMMU
space:

enum iommu_cap {
	IOMMU_CAP_CACHE_COHERENCY,
--->    IOMMU_CAP_INTR_REMAP,
	IOMMU_CAP_NOEXEC,
};

But it seems to be not a good idea to use
bus_set_iommu() to add this flag on PPC64 which
never set/use iommu_ops.

Eric also posted a patchset [1] to abstract
this capability on MSI controller side for ARM.
But I found we also never use msi_domain_info
on PPC64. We have to rework the MSI code on
PPC64 to support msi_domain_ops if we want to
use msi_domain_info.

Then I noticed that interrupt remapping is
abstracted on PCI host bridge side on PPC64.
So I'm thinking whether we could add a new
bit to pci_bus_flags to indicate this
capability, like this patch does.

Compared with IOMMU_CAP_INTR_REMAP, this
flag is more common. Any arch can set/use this
easily. And it can provide a better granularity
(pci_bus_type -> pci_bus).

[1] http://www.spinics.net/lists/kvm/msg130262.html

Signed-off-by: Yongji Xie <xyjxie@xxxxxxxxxxxxxxxxxx>
---
 arch/powerpc/platforms/powernv/pci-ioda.c |    8 ++++++++
 include/linux/pci.h                       |    1 +
 2 files changed, 9 insertions(+)

diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
index f90dc04..9557638 100644
--- a/arch/powerpc/platforms/powernv/pci-ioda.c
+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
@@ -3080,6 +3080,12 @@ static void pnv_pci_ioda_fixup(void)
 	pnv_npu_ioda_fixup();
 }
 
+int pnv_pci_ioda_root_bridge_prepare(struct pci_host_bridge *bridge)
+{
+	bridge->bus->bus_flags |= PCI_BUS_FLAGS_MSI_REMAP;
+	return 0;
+}
+
 /*
  * Returns the alignment for I/O or memory windows for P2P
  * bridges. That actually depends on how PEs are segmented.
@@ -3364,6 +3370,8 @@ static void __init pnv_pci_init_ioda_phb(struct device_node *np,
 	 */
 	ppc_md.pcibios_fixup = pnv_pci_ioda_fixup;
 
+	ppc_md.pcibios_root_bridge_prepare = pnv_pci_ioda_root_bridge_prepare;
+
 	if (phb->type == PNV_PHB_NPU)
 		hose->controller_ops = pnv_npu_ioda_controller_ops;
 	else
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 27df4a6..741dcaf 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -193,6 +193,7 @@ typedef unsigned short __bitwise pci_bus_flags_t;
 enum pci_bus_flags {
 	PCI_BUS_FLAGS_NO_MSI   = (__force pci_bus_flags_t) 1,
 	PCI_BUS_FLAGS_NO_MMRBC = (__force pci_bus_flags_t) 2,
+	PCI_BUS_FLAGS_MSI_REMAP = (__force pci_bus_flags_t) 3,
 };
 
 /* These values come from the PCI Express Spec */
-- 
1.7.9.5