[PATCH 10/25] PCI: Add pci_resource_num() helper

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

A few places in PCI code, mainly in setup-bus.c, need to reverse lookup
the index of a resource in pci_dev's resource array. Create
pci_resource_num() helper to avoid repeating the pointer arithmetic
trick used to calculate the index.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
 drivers/pci/pci.h       | 24 +++++++++++++++++++++++-
 drivers/pci/setup-bus.c | 10 +++++-----
 2 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 25bae4bfebea..0b722d158b6a 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -330,6 +330,28 @@ void pci_walk_bus_locked(struct pci_bus *top,
 
 const char *pci_resource_name(struct pci_dev *dev, unsigned int i);
 
+/**
+ * pci_resource_num - Reverse lookup resource number from device resources
+ * @dev: PCI device
+ * @res: Resource to lookup index for (MUST be a @dev's resource)
+ *
+ * Perform reverse lookup to determine the resource number for @res within
+ * @dev resource array. NOTE: The caller is responsible for ensuring @res is
+ * among @dev's resources!
+ *
+ * Returns: resource number.
+ */
+static inline int pci_resource_num(const struct pci_dev *dev,
+				   const struct resource *res)
+{
+	int resno = res - &dev->resource[0];
+
+	/* Passing a resource that is not among dev's resources? */
+	WARN_ON_ONCE(resno >= PCI_NUM_RESOURCES);
+
+	return resno;
+}
+
 void pci_reassigndev_resource_alignment(struct pci_dev *dev);
 void pci_disable_bridge_window(struct pci_dev *dev);
 struct pci_bus *pci_bus_get(struct pci_bus *bus);
@@ -682,7 +704,7 @@ unsigned long pci_cardbus_resource_alignment(struct resource *);
 static inline resource_size_t pci_resource_alignment(struct pci_dev *dev,
 						     struct resource *res)
 {
-	int resno = res - dev->resource;
+	int resno = pci_resource_num(dev, res);
 
 	if (pci_resource_is_iov(resno))
 		return pci_sriov_resource_alignment(dev, resno);
diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index 63c134b087d5..8831365418d6 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -242,7 +242,7 @@ static void reassign_resources_sorted(struct list_head *realloc_head,
 		if (!found_match) /* Just skip */
 			continue;
 
-		idx = res - &add_res->dev->resource[0];
+		idx = pci_resource_num(add_res->dev, res);
 		res_name = pci_resource_name(add_res->dev, idx);
 		add_size = add_res->add_size;
 		align = add_res->min_align;
@@ -284,7 +284,7 @@ static void assign_requested_resources_sorted(struct list_head *head,
 
 	list_for_each_entry(dev_res, head, list) {
 		res = dev_res->res;
-		idx = res - &dev_res->dev->resource[0];
+		idx = pci_resource_num(dev_res->dev, res);
 
 		if (!resource_size(res))
 			continue;
@@ -2211,7 +2211,7 @@ void pci_assign_unassigned_root_bus_resources(struct pci_bus *bus)
 		res->flags = fail_res->flags;
 
 		if (pci_is_bridge(fail_res->dev)) {
-			idx = res - &fail_res->dev->resource[0];
+			idx = pci_resource_num(fail_res->dev, res);
 			if (idx >= PCI_BRIDGE_RESOURCES &&
 			    idx <= PCI_BRIDGE_RESOURCE_END)
 				res->flags = 0;
@@ -2295,7 +2295,7 @@ void pci_assign_unassigned_bridge_resources(struct pci_dev *bridge)
 		res->flags = fail_res->flags;
 
 		if (pci_is_bridge(fail_res->dev)) {
-			idx = res - &fail_res->dev->resource[0];
+			idx = pci_resource_num(fail_res->dev, res);
 			if (idx >= PCI_BRIDGE_RESOURCES &&
 			    idx <= PCI_BRIDGE_RESOURCE_END)
 				res->flags = 0;
@@ -2402,7 +2402,7 @@ int pci_reassign_bridge_resources(struct pci_dev *bridge, unsigned long type)
 		struct resource *res = dev_res->res;
 
 		bridge = dev_res->dev;
-		i = res - bridge->resource;
+		i = pci_resource_num(bridge, res);
 
 		res->start = dev_res->start;
 		res->end = dev_res->end;
-- 
2.39.5