On Tue, Feb 13, 2018 at 5:31 PM, Mika Westerberg
<mika.westerberg@xxxxxxxxxxxxxxx> wrote:
> When distributing extra buses between hotplug bridges we need to make
> sure each bridge reserve at least one bus number, even if there is
> currently nothing connected to it. For instance ACPI hotplug may bring
> in additional devices to non-hotplug bridges later on. To make sure we
> don't run out of bus numbers for non-hotplug bridges reserve one bus
> number for them upfront before distributing buses for hotplug bridges.
>
> Fixes: 1c02ea810065 ("PCI: Distribute available buses to hotplug-capable bridges")
> Reported-by: Mario Limonciello <mario.limonciello@xxxxxxxx>
> Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
Just a few notation-related nits below.
> ---
> drivers/pci/probe.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index ef5377438a1e..3e91d2191a7d 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2561,7 +2561,8 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
> for_each_pci_bridge(dev, bus) {
> cmax = max;
> max = pci_scan_bridge_extend(bus, dev, max, 0, 0);
> - used_buses += cmax - max;
> + /* Reserve one bus for each bridge */
> + used_buses += cmax - max ?: 1;
I would write this as
used_buses++;
if (cmax - max > 1)
used_buses += cmax - max - 1;
to make this and the new code below look analogous.
> }
>
> /* Scan bridges that need to be reconfigured */
> @@ -2584,12 +2585,14 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
> * bridges if any.
> */
> buses = available_buses / hotplug_bridges;
> - buses = min(buses, available_buses - used_buses);
> + buses = min(buses, available_buses - (used_buses - 1));
You can write the inner expression as "available_buses - used_buses +
1" (without the extra parens).
> }
>
> cmax = max;
> max = pci_scan_bridge_extend(bus, dev, cmax, buses, 1);
> - used_buses += max - cmax;
> + /* One bus is already accounted so don't add it again */
> + if (max - cmax > 1)
> + used_buses += (max - cmax) - 1;
The parens on the right-hand side are not necessary here AFAICS.
> }
>
> /*
> --
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