[PATCH v2 1/4] PCI: Clean up pci_scan_slot()

Niklas Schnelle
2022-04-12T14:30:52Z

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 duplicating the code from the scan loop and
splitting the condition that the first function exits from it being
multifunction which is tested in next_fn().

Furthermore the non ARI branch of next_fn() mixes the case that
multifunction devices may have non-contiguous function ranges and dev
may thus be NULL with the multifunction requirement. It also signals
that no further functions need to be scanned by returning 0 which is
a valid function number.

Improve upon this by moving all conditions for having to scan for more
functions into next_fn() and make them obvious and commented.

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.

No functional change is intended.

Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
---
drivers/pci/probe.c | 41 +++++++++++++++++++----------------------
1 file changed, 19 insertions(+), 22 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 17a969942d37..389aa1f9cb2c 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2579,33 +2579,35 @@ 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;
unsigned int next_fn;

- if (pci_ari_enabled(bus)) {
- if (!dev)
- return 0;
+ if (dev && pci_ari_enabled(bus)) {
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;
-
- return 0;
+ /* only multifunction devices may have more functions */
+ if (dev && !dev->multifunction)
+ return -ENODEV;
+ /*
+ * A function 0 is required but multifunction devices may
+ * be non-contiguous so dev can be NULL otherwise.
+ */
+ if (!fn && !dev)
+ return -ENODEV;
+ return (fn <= 6) ? fn + 1 : -ENODEV;
}

static int only_one_child(struct pci_bus *bus)
@@ -2643,24 +2645,19 @@ 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, nr = 0;
+ struct pci_dev *dev = NULL;

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)) {
+ for (fn = 0; fn >= 0; fn = next_fn(bus, dev, fn)) {
dev = pci_scan_single_device(bus, devfn + fn);
if (dev) {
if (!pci_dev_is_added(dev))
nr++;
- dev->multifunction = 1;
+ if (nr > 1)
+ dev->multifunction = 1;
}
}

--
2.32.0