[PATCH v8 4/7] PCI: Document pci_bus_for_each_resource() to avoid confusion

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

There might be a confusion with the implementation of the
pci_bus_for_each_resources() due to side effect of Logical
OR. Document entire macro and explain how it works and why
the conditional needs to be like that.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
---
 include/linux/pci.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/include/linux/pci.h b/include/linux/pci.h
index 5cacd9e4c8cd..e3b3af606280 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1446,6 +1446,26 @@ int devm_request_pci_bus_resources(struct device *dev,
 /* Temporary until new and working PCI SBR API in place */
 int pci_bridge_secondary_bus_reset(struct pci_dev *dev);
 
+/**
+ * pci_bus_for_each_resource - iterate over PCI bus resources
+ * @bus: the PCI bus
+ * @res: a varible to keep a pointer to the current resource
+ * @i: a variable to keep the index of the current resource
+ *
+ * Iterate over PCI bus resources. The first part is to go over PCI bus
+ * resource array, which has at most the %PCI_BRIDGE_RESOURCE_NUM entries.
+ * After that continue with the separate list of the additional resources,
+ * if not empty. That's why the Logical OR is being used.
+ *
+ * Possible usage:
+ *
+ *     struct pci_bus *bus = ...;
+ *     struct resource *res;
+ *     unsigned int i;
+ *
+ *     pci_bus_for_each_resource(bus, res, i)
+ *             pr_info("PCI bus resource[%u]: %pR\n", i, res);
+ */
 #define pci_bus_for_each_resource(bus, res, i)                         \
        for (i = 0;                                                     \
            (res = pci_bus_resource_n(bus, i)) || i < PCI_BRIDGE_RESOURCE_NUM; \
-- 
2.40.0.1.gaa8946217a0b