Re: Behavior of the PM framework w.r.t the parent-child relationship

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

+ linux-pci

On Mon, Apr 22, 2024 at 03:30:18PM +0530, Krishna Chaitanya Chundru wrote:
> Hi Rafael,
> 
> We are planning to add runtime PM support to the PCIe controller driver
> and facing some issues with runtime PM. These are the details.
> 
> PCIe controller is a parent of the PCIe bridge dev node and PCIe
> endpoint driver as shown below
> 
> PCIe controller(Top level parent & parent of host bridge)
>                         |
>                         v
>         PCIe Host bridge(Parent of PCI-PCI bridge driver)
>                         |
>                         v
>         PCI-PCI bridge(Parent of endpoint driver)
>                         |
>                         v
>                PCIe endpoint driver
> 
> There is no driver associated with the PCIe Host bridge device node.
> And the runtime pm for the bridge node is not enabled explicitly.
> 
> we are seeing PCIe controller driver is getting runtime suspended even
> when the PCI-PCI bridge and PCIe endpoint driver are active.
> Our expectation is controller driver runtime suspend will be called only
> when the child drivers went to the runtime suspend as the controller
> is parent device.
> 
> For the things to work properly we are calling pm_runtime_set_active() &
> pm_runtime_enable() in [1]
> 
> As bridge device node doesn't have driver associated and it is kind of
> integrated with the controller, So we are expecting when the controller
> driver enables its runtime pm it should enable the bridge runtime pm
> also and vice versa.
> 
> Can you please check this behavior and see if it is something which
> needs to be fixed at the PM framework.
> 

Hi Rafael,

Gentle ping on this thread!

- Mani

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