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

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Message-ID: <Z30p2Etwf3F2AUvD@hovoldconsulting.com>
Date: Tue, 7 Jan 2025 14:19:20 +0100
From: Johan Hovold <johan@...nel.org>
To: Krishna chaitanya chundru <quic_krichai@...cinc.com>
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 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:

	pci0004:00: pcie4: Enabling runtime PM for inactive device with active children

which may have unpopulated ports (this laptop SKU does not have a modem).

Reverting dc421bb3c0db ("PCI: Enable runtime PM of the host bridge")
makes the warning go away.

Johan


#regzbot introduced: dc421bb3c0db