Re: [RESEND PATCH v5] PCI: Make sure the bus bridge powered on when scanning bus

From: Yicong Yang <yangyicong@huawei.com>
To: <bhelgaas@google.com>, <linux-pci@vger.kernel.org>
Cc: <linux-kernel@vger.kernel.org>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>
Subject: Re: [RESEND PATCH v5] PCI: Make sure the bus bridge powered on when scanning bus
Date: Tue, 17 May 2022 20:48:13 +0800	[thread overview]
Message-ID: <eb120037-d22b-15ca-1bb0-8bfe728a6055@huawei.com> (raw)
In-Reply-To: <20220517124319.47125-1-yangyicong@hisilicon.com>

On 2022/5/17 20:43, 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 a Root Port and it is runtime-suspended, so
> 0000:81:00.1 is unreachable after a rescan.
> 
> Power up the bridge when scanning the child bus and allow it to
> suspend again by adding pm_runtime_get_sync()/pm_runtime_put()
> in pci_scan_child_bus_extend().
> 
> Cc: Rafael J. Wysocki <rafael@kernel.org>
> Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
> Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---

Attach the change log here. Sorry for my forgetness..

Change since v4:
- rephrase the commit suggested by Rafael
Link: https://lore.kernel.org/lkml/20220422080404.27724-1-yangyicong@hisilicon.com/

Change since v3:
- retain the pm_runtime_*() calls in pci_scan_bridge_extend() as Rafael points
  out that it's necessary when the brigde is in D3cold
Link: https://lore.kernel.org/linux-pci/20220414123736.34150-1-yangyicong@hisilicon.com/

Change since v2:
- just rebase it on v5.18-rc2
Link: https://lore.kernel.org/linux-pci/1601029386-4928-1-git-send-email-yangyicong@hisilicon.com/

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@hisilicon.com/

>  drivers/pci/probe.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 17a969942d37..b108e72b6586 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2859,11 +2859,20 @@ 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 *bridge = bus->self;
>  	struct pci_dev *dev;
>  	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 +2985,9 @@ 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
> 