[PATCH v3 4/6] powerpc/powernv: replace the hard coded boundary with gate

[Wei Yang <weiyang@linux.vnet.ibm.com>]

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 (m64_segsize >> 1) and adds
comment to explain the reason for it.

Signed-off-by: Wei Yang <weiyang@linux.vnet.ibm.com>
---
 arch/powerpc/platforms/powernv/pci-ioda.c |   22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
index 4da0f50..3e8c0b4 100644
--- a/arch/powerpc/platforms/powernv/pci-ioda.c
+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
@@ -2688,7 +2688,7 @@ static void pnv_pci_ioda_fixup_iov_resources(struct pci_dev *pdev)
 	struct pnv_phb *phb;
 	struct resource *res;
 	int i;
-	resource_size_t size;
+	resource_size_t size, gate;
 	struct pci_dn *pdn;
 	int mul, total_vfs;
 
@@ -2704,6 +2704,17 @@ static void pnv_pci_ioda_fixup_iov_resources(struct pci_dev *pdev)
 
 	total_vfs = pci_sriov_get_totalvfs(pdev);
 	mul = phb->ioda.total_pe;
+	/*
+	 * If bigger than or equal to half 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.
+	 */
+	gate = phb->ioda.m64_segsize >> 1;
 
 	for (i = 0; i < PCI_SRIOV_NUM_BARS; i++) {
 		res = &pdev->resource[i + PCI_IOV_RESOURCES];
@@ -2718,10 +2729,11 @@ 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);
+		/* bigger than or equal to gate */
+		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;
-- 
1.7.9.5