linux-kernel - Re: [PATCH v7 2/2] PCI: Enable runtime pm of the host bridge

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Message-ID: <7882105f-93a3-fab9-70a2-2dc55d6becfc@quicinc.com>
Date: Tue, 7 Jan 2025 19:40:39 +0530
From: Krishna Chaitanya Chundru <quic_krichai@...cinc.com>
To: Johan Hovold <johan@...nel.org>
CC: Kevin Xie <kevin.xie@...rfivetech.com>,
        Lorenzo Pieralisi
	<lpieralisi@...nel.org>,
        Krzysztof Wilczyński
	<kw@...ux.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        "Rob Herring" <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
        <Markus.Elfring@....de>, <quic_mrana@...cinc.com>, <rafael@...nel.org>,
        <m.szyprowski@...sung.com>, <linux-pm@...r.kernel.org>,
        <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <regressions@...ts.linux.dev>
Subject: Re: [PATCH v7 2/2] PCI: Enable runtime pm of the host bridge



On 1/7/2025 6:49 PM, Johan Hovold wrote:
> On Mon, Nov 11, 2024 at 02:11:53PM +0530, Krishna chaitanya chundru wrote:
>> The Controller driver is the parent device of the PCIe host bridge,
>> PCI-PCI bridge and PCIe endpoint as shown below.
>>
>>          PCIe controller(Top level parent & parent of host bridge)
>>                          |
>>                          v
>>          PCIe Host bridge(Parent of PCI-PCI bridge)
>>                          |
>>                          v
>>          PCI-PCI bridge(Parent of endpoint driver)
>>                          |
>>                          v
>>                  PCIe endpoint driver
>>
>> Now, when the controller device goes to runtime suspend, PM framework
>> will check the runtime PM state of the child device (host bridge) and
>> will find it to be disabled. So it will allow the parent (controller
>> device) to go to runtime suspend. Only if the child device's state was
>> 'active' it will prevent the parent to get suspended.
> 
>> Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
>> Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
> 
>> @@ -3106,6 +3106,17 @@ int pci_host_probe(struct pci_host_bridge *bridge)
>>   		pcie_bus_configure_settings(child);
>>   
>>   	pci_bus_add_devices(bus);
>> +
>> +	/*
>> +	 * Ensure pm_runtime_enable() is called for the controller drivers,
>> +	 * before calling pci_host_probe() as pm frameworks expects if the
>> +	 * parent device supports runtime pm then it needs to enabled before
>> +	 * child runtime pm.
>> +	 */
>> +	pm_runtime_set_active(&bridge->dev);
>> +	pm_runtime_no_callbacks(&bridge->dev);
>> +	devm_pm_runtime_enable(&bridge->dev);
>> +
>>   	return 0;
>>   }
>>   EXPORT_SYMBOL_GPL(pci_host_probe);
> 
> I just noticed that this change in 6.13-rc1 is causing the following
> warning on resume from suspend on machines like the Lenovo ThinkPad
> X13s:
>
Hi Johan,

Can you confirm if you are seeing this issue is seen in the boot-up
case also. As this part of the code executes only at the boot time and
will not have effect in resume from suspend.

> 	pci0004:00: pcie4: Enabling runtime PM for inactive device with active children
> 
I believe this is not causing any functional issues.
> which may have unpopulated ports (this laptop SKU does not have a modem).
> 
Can you confirm if this warning goes away if there is some endpoint
connected to it.

- Krishna Chaitanya.
> Reverting dc421bb3c0db ("PCI: Enable runtime PM of the host bridge")
> makes the warning go away.
> 
> Johan
> 
> 
> #regzbot introduced: dc421bb3c0db