[+cc Rafael, linux-pm, since I'd really like his ack/review]
On Thu, Apr 14, 2022 at 08:37:36PM +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().
>
> A similar issue is met and solved by
> d963f6512e15 ("PCI: Power on bridges before scanning new devices")
> which rescan the devices through /sys/bus/pci/devices/0000:80:00.0/rescan.
> The callstack is like:
>
> dev_rescan_restore()
> pci_rescan_bus()
> pci_scan_bridge_extend()
> pci_scan_child_bus_extend() /* will wake up the bridge with this patch */
>
> With this patch the issue is also resolved, so let's remove the calls of
> pm_runtime_*() in pci_scan_bridge_extend().
>
> Cc: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Signed-off-by: Yicong Yang <yangyicong@xxxxxxxxxxxxx>
> ---
> Change since v2:
> - just rebase it on v5.18-rc2
> Link: https://lore.kernel.org/linux-pci/1601029386-4928-1-git-send-email-yangyicong@xxxxxxxxxxxxx/
>
> Change since v1:
> - use an intermediate variable *bridge as suggested
> - remove the pm_runtime_*() calls in pci_scan_bridge_extend()
> Link: https://lore.kernel.org/linux-pci/1596022223-4765-1-git-send-email-yangyicong@xxxxxxxxxxxxx/
>
> drivers/pci/probe.c | 21 ++++++++++++---------
> 1 file changed, 12 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 17a969942d37..2ca6b4b708e3 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1257,12 +1257,6 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
> u8 fixed_sec, fixed_sub;
> int next_busnr;
>
> - /*
> - * Make sure the bridge is powered on to be able to access config
> - * space of devices below it.
> - */
> - pm_runtime_get_sync(&dev->dev);
> -
> pci_read_config_dword(dev, PCI_PRIMARY_BUS, &buses);
> primary = buses & 0xFF;
> secondary = (buses >> 8) & 0xFF;
> @@ -1464,8 +1458,6 @@ static int pci_scan_bridge_extend(struct pci_bus *bus, struct pci_dev *dev,
> out:
> pci_write_config_word(dev, PCI_BRIDGE_CONTROL, bctl);
>
> - pm_runtime_put(&dev->dev);
> -
> return max;
> }
>
> @@ -2859,11 +2851,19 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
> unsigned int used_buses, normal_bridges = 0, hotplug_bridges = 0;
> unsigned int start = bus->busn_res.start;
> unsigned int devfn, fn, cmax, max = start;
> - struct pci_dev *dev;
> + struct pci_dev *dev, *bridge = bus->self;
> int nr_devs;
>
> 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 (bridge)
> + pm_runtime_get_sync(&bridge->dev);
> +
> /* Go find them, Rover! */
> for (devfn = 0; devfn < 256; devfn += 8) {
> nr_devs = pci_scan_slot(bus, devfn);
> @@ -2976,6 +2976,9 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
> }
> }
>
> + 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
> --
> 2.24.0
>
