PCI: Clean up pci_scan_slot()

While determining the next PCI function is factored out of pci_scan_slot()
into next_fn(), the former still handles the first function as a special
case, which duplicates the code from the scan loop.

Furthermore the non-ARI branch of next_fn() is generally hard to understand
and especially the check for multifunction devices is hidden in the
handling of NULL devices for non-contiguous multifunction. It also signals
that no further functions need to be scanned by returning 0 via wraparound
and this is a valid function number.

Improve upon this by transforming the conditions in next_fn() to be easier
to understand.

By changing next_fn() to return -ENODEV instead of 0 when there is no next
function we can then handle the initial function inside the loop and
deduplicate the shared handling. This also makes it more explicit that only
function 0 must exist.

No functional change is intended.

Link: https://lore.kernel.org/r/20220628143100.3228092-2-schnelle@linux.ibm.com
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Jan Kiszka <jan.kiszka@siemens.com>

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 17a9699..b05d0ed 100644 (file)
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2579,8 +2579,7 @@ struct pci_dev *pci_scan_single_device(struct pci_bus *bus, int devfn)
 }
 EXPORT_SYMBOL(pci_scan_single_device);
 
-static unsigned int next_fn(struct pci_bus *bus, struct pci_dev *dev,
-                           unsigned int fn)
+static int next_fn(struct pci_bus *bus, struct pci_dev *dev, int fn)
 {
        int pos;
        u16 cap = 0;
@@ -2588,24 +2587,26 @@ static unsigned int next_fn(struct pci_bus *bus, struct pci_dev *dev,
 
        if (pci_ari_enabled(bus)) {
                if (!dev)
-                       return 0;
+                       return -ENODEV;
                pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ARI);
                if (!pos)
-                       return 0;
+                       return -ENODEV;
 
                pci_read_config_word(dev, pos + PCI_ARI_CAP, &cap);
                next_fn = PCI_ARI_CAP_NFN(cap);
                if (next_fn <= fn)
-                       return 0;       /* protect against malformed list */
+                       return -ENODEV; /* protect against malformed list */
 
                return next_fn;
        }
 
-       /* dev may be NULL for non-contiguous multifunction devices */
-       if (!dev || dev->multifunction)
-               return (fn + 1) % 8;
+       if (fn >= 7)
+               return -ENODEV;
+       /* only multifunction devices may have more functions */
+       if (dev && !dev->multifunction)
+               return -ENODEV;
 
-       return 0;
+       return fn + 1;
 }
 
 static int only_one_child(struct pci_bus *bus)
@@ -2643,26 +2644,25 @@ static int only_one_child(struct pci_bus *bus)
  */
 int pci_scan_slot(struct pci_bus *bus, int devfn)
 {
-       unsigned int fn, nr = 0;
        struct pci_dev *dev;
+       int fn = 0, nr = 0;
 
        if (only_one_child(bus) && (devfn > 0))
                return 0; /* Already scanned the entire slot */
 
-       dev = pci_scan_single_device(bus, devfn);
-       if (!dev)
-               return 0;
-       if (!pci_dev_is_added(dev))
-               nr++;
-
-       for (fn = next_fn(bus, dev, 0); fn > 0; fn = next_fn(bus, dev, fn)) {
+       do {
                dev = pci_scan_single_device(bus, devfn + fn);
                if (dev) {
                        if (!pci_dev_is_added(dev))
                                nr++;
-                       dev->multifunction = 1;
+                       if (fn > 0)
+                               dev->multifunction = 1;
+               } else if (fn == 0) {
+                       /* function 0 is required */
+                       break;
                }
-       }
+               fn = next_fn(bus, dev, fn);
+       } while (fn >= 0);
 
        /* Only one slot has PCIe device */
        if (bus->self && nr)