powerpc/powernv: replace the hard coded boundary with gate

At the moment 64bit-prefetchable window can be maximum 64GB, which is
currently got from device tree. This means that in shared mode the maximum
supported VF BAR size is 64GB/256=256MB. While this size could exhaust the
whole 64bit-prefetchable window. This is a design decision to set a
boundary to 64MB of the VF BAR size. Since VF BAR size with 64MB would
occupy a quarter of the 64bit-prefetchable window, this is affordable.

This patch replaces magic limit of 64MB with "gate", which is 1/4 of the
M64 Segment Size(m64_segsize >> 2) and adds comment to explain the reason
for it.

Signed-off-by: Wei Yang <weiyang@linux.vnet.ibm.com>
Reviewed-by: Gavin Shan <gwshan@linux.vent.ibm.com>
Acked-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
index 4004c0a..b8c01fc 100644 (file)
--- a/arch/powerpc/platforms/powernv/pci-ioda.c
+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
@@ -2798,8 +2798,9 @@ static void pnv_pci_init_ioda_msis(struct pnv_phb *phb) { }
 #ifdef CONFIG_PCI_IOV
 static void pnv_pci_ioda_fixup_iov_resources(struct pci_dev *pdev)
 {
-       struct pci_controller *hose;
-       struct pnv_phb *phb;
+       struct pci_controller *hose = pci_bus_to_host(pdev->bus);
+       struct pnv_phb *phb = hose->private_data;
+       const resource_size_t gate = phb->ioda.m64_segsize >> 2;
        struct resource *res;
        int i;
        resource_size_t size;
@@ -2809,9 +2810,6 @@ static void pnv_pci_ioda_fixup_iov_resources(struct pci_dev *pdev)
        if (!pdev->is_physfn || pdev->is_added)
                return;
 
-       hose = pci_bus_to_host(pdev->bus);
-       phb = hose->private_data;
-
        pdn = pci_get_pdn(pdev);
        pdn->vfs_expanded = 0;
        pdn->m64_single_mode = false;
@@ -2832,10 +2830,22 @@ static void pnv_pci_ioda_fixup_iov_resources(struct pci_dev *pdev)
 
                size = pci_iov_resource_size(pdev, i + PCI_IOV_RESOURCES);
 
-               /* bigger than 64M */
-               if (size > (1 << 26)) {
-                       dev_info(&pdev->dev, "PowerNV: VF BAR%d: %pR IOV size is bigger than 64M, roundup power2\n",
-                                i, res);
+               /*
+                * If bigger than quarter of M64 segment size, just round up
+                * power of two.
+                *
+                * Generally, one M64 BAR maps one IOV BAR. To avoid conflict
+                * with other devices, IOV BAR size is expanded to be
+                * (total_pe * VF_BAR_size).  When VF_BAR_size is half of M64
+                * segment size , the expanded size would equal to half of the
+                * whole M64 space size, which will exhaust the M64 Space and
+                * limit the system flexibility.  This is a design decision to
+                * set the boundary to quarter of the M64 segment size.
+                */
+               if (size > gate) {
+                       dev_info(&pdev->dev, "PowerNV: VF BAR%d: %pR IOV size "
+                               "is bigger than %lld, roundup power2\n",
+                                i, res, gate);
                        mul = roundup_pow_of_two(total_vfs);
                        pdn->m64_single_mode = true;
                        break;