[+cc Mika, Rafael, Peter]
On Wed, Jul 29, 2020 at 07:30:23PM +0800, Yicong Yang wrote:
> When the bus bridge is runtime suspended, we'll fail to rescan
> the devices through sysfs as we cannot access the configuration
> space correctly when the bridge is in D3hot.
> It can be reproduced like:
>
> $ echo 1 > /sys/bus/pci/devices/0000:80:00.0/0000:81:00.1/remove
> $ echo 1 > /sys/bus/pci/devices/0000:80:00.0/pci_bus/0000:81/rescan
>
> 0000:80:00.0 is root port and is runtime suspended and we cannot
> get 0000:81:00.1 after rescan.
>
> Make bridge powered on when scanning the child bus, by adding
> pm_runtime_get_sync()/pm_runtime_put() in pci_scan_child_bus_extend().
>
> Signed-off-by: Yicong Yang <yangyicong@xxxxxxxxxxxxx>
> ---
> drivers/pci/probe.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 2f66988..5bb502b 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2795,6 +2795,14 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
>
> dev_dbg(&bus->dev, "scanning bus\n");
>
> + /*
> + * Make sure the bus bridge is powered on, otherwise we may not be
> + * able to scan the devices as we may fail to access the configuration
> + * space of subordinates.
> + */
> + if (bus->self)
> + pm_runtime_get_sync(&bus->self->dev);
I think if we do this, we should be able to remove the call from
pci_scan_bridge() added by d963f6512e15 ("PCI: Power on bridges before
scanning new devices"), right?
The reason we need it here is because there are two paths to
pci_scan_child_bus_extend() and only one of them calls
pm_runtime_get_sync():
pci_scan_bridge_extend
pm_runtime_get_sync
pci_scan_child_bus_extend
pci_scan_child_bus
pci_scan_child_bus_extend
If we move the pm_runtime_get_sync() from pci_scan_bridge_extend() to
pci_scan_child_bus_extend(), both paths should be safe.
> /* Go find them, Rover! */
> for (devfn = 0; devfn < 256; devfn += 8) {
> nr_devs = pci_scan_slot(bus, devfn);
> @@ -2907,6 +2915,9 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
> }
> }
>
> + if (bus->self)
> + pm_runtime_put(&bus->self->dev);
I would probably do this:
struct pci_dev *bridge = bus->self;
if (bridge)
pm_runtime_get_sync(&bridge->dev);
...
if (bridge)
pm_runtime_put(&bridge->dev);
> /*
> * We've scanned the bus and so we know all about what's on
> * the other side of any bridges that may be on this bus plus
> --
> 2.8.1
>
