On 6/30/22 15:48, Niklas Schnelle wrote:
On Thu, 2022-06-30 at 14:40 +0200, Pierre Morel wrote:
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 ?
The "% 8" became unnecessary due to the explicit "if (fn >= 7)"
above.
The original "% 8" did what I referred to in the commit message with
"It [the function] also signals that no further functions need to be
scanned by returning 0 via wraparound and this is a valid function
number.". Instead we now explicitly return -ENODEV in this case.
Yes it goes with it.
With this code next_fn returns -ENODEV for fn = 8 instead of previously
returning 1. (If I am right)
With the previous code, did we assume that next_fn is never called with
fn > 7?
I guess yes as we test pci_ari_enabled first and without ARI we do not
have more than 7 more functions. is it right?
For what I think this new code seems better as it does not make the
assumption that it get called with fn < 8.
}
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
Thanks for taking a look!
--
Pierre Morel
IBM Lab Boeblingen
