[PATCH v6 1/5] PCI: Clean up pci_scan_slot()

Niklas Schnelle
2022-06-28T14:31:15Z

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. This 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.

Cc: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
---
drivers/pci/probe.c | 38 +++++++++++++++++++-------------------
1 file changed, 19 insertions(+), 19 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 17a969942d37..b05d0ed83a24 100644
--- 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)
--
2.32.0