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

Pierre Morel
2022-06-30T12:36:16Z

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@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;

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