linux-kernel - Re: [PATCH v4] PCI: Enable runtime pm of the host bridge

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Message-ID: <20240708073056.GC3866@thinkpad>
Date: Mon, 8 Jul 2024 13:00:56 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Krishna chaitanya chundru <quic_krichai@...cinc.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, quic_vbadigan@...cinc.com,
	quic_ramkri@...cinc.com, quic_nitegupt@...cinc.com,
	quic_skananth@...cinc.com, quic_parass@...cinc.com
Subject: Re: [PATCH v4] PCI: Enable runtime pm of the host bridge

On Mon, Jul 08, 2024 at 10:19:40AM +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.
> 
> Since runtime PM is disabled for host bridge, the state of the child
> devices under the host bridge is not taken into account by PM framework
> for the top level parent, PCIe controller. So PM framework, allows
> the controller driver to enter runtime PM irrespective of the state
> of the devices under the host bridge. And this causes the topology
> breakage and also possible PM issues like controller driver goes to
> runtime suspend while endpoint driver is doing some transfers.
> 
> So enable runtime PM for the host bridge, so that controller driver
> goes to suspend only when all child devices goes to runtime suspend.
> 
> Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>

Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

Note to the maintainers: This patch should be applied at the start of the RC
window to give enough testing in linux-next since it touches the PM of all host
bridges.

- Mani

> ---
> Changes in v4:
> - Changed pm_runtime_enable() to devm_pm_runtime_enable() (suggested by mayank)
> - Link to v3: https://lore.kernel.org/lkml/20240609-runtime_pm-v3-1-3d0460b49d60@quicinc.com/
> Changes in v3:
> - Moved the runtime API call's from the dwc driver to PCI framework
>   as it is applicable for all (suggested by mani)
> - Updated the commit message.
> - Link to v2: https://lore.kernel.org/all/20240305-runtime_pm_enable-v2-1-a849b74091d1@quicinc.com
> Changes in v2:
> - Updated commit message as suggested by mani.
> - Link to v1: https://lore.kernel.org/r/20240219-runtime_pm_enable-v1-1-d39660310504@quicinc.com
> ---
> 
> ---
>  drivers/pci/probe.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 8e696e547565..fd49563a44d9 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -3096,6 +3096,10 @@ int pci_host_probe(struct pci_host_bridge *bridge)
>  	}
>  
>  	pci_bus_add_devices(bus);
> +
> +	pm_runtime_set_active(&bridge->dev);
> +	devm_pm_runtime_enable(&bridge->dev);
> +
>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(pci_host_probe);
> 
> ---
> base-commit: 1613e604df0cd359cf2a7fbd9be7a0bcfacfabd0
> change-id: 20240708-runtime_pm-978ccbca6130
> 
> Best regards,
> -- 
> Krishna chaitanya chundru <quic_krichai@...cinc.com>
> 

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