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

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On 6/28/22 16:30, Niklas Schnelle wrote:
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@xxxxxxxxxxx>
Signed-off-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
---
  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;

No more % 8 ?
Even it disapear later shouldn't we keep it ?



  }
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)


Otherwise LGTM


--
Pierre Morel
IBM Lab Boeblingen



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