linux-kernel - Re: [PATCH 1/3] PCI: host-common: Add an API to check for any device under the Root Ports

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Message-ID: <4aface5d-66eb-41bb-b6f3-ee8ce5d5da6b@oss.qualcomm.com>
Date: Thu, 6 Nov 2025 10:47:48 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>,
        lpieralisi@...nel.org, kwilczynski@...nel.org, mani@...nel.org,
        bhelgaas@...gle.com
Cc: will@...nel.org, linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        robh@...nel.org, linux-arm-msm@...r.kernel.org,
        zhangsenchuan@...incomputing.com
Subject: Re: [PATCH 1/3] PCI: host-common: Add an API to check for any device
 under the Root Ports

On 11/6/25 7:13 AM, Manivannan Sadhasivam wrote:
> Some controller drivers need to check if there is any device available
> under the Root Ports. So add an API that returns 'true' if a device is
> found under any of the Root Ports, 'false' otherwise.
> 
> Controller drivers can use this API for usecases like turning off the
> controller resources only if there are no devices under the Root Ports,
> skipping PME_Turn_Off broadcast etc...
> 
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
> ---
>  drivers/pci/controller/pci-host-common.c | 21 +++++++++++++++++++++
>  drivers/pci/controller/pci-host-common.h |  2 ++
>  2 files changed, 23 insertions(+)
> 
> diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
> index 810d1c8de24e..6b4f90903dc6 100644
> --- a/drivers/pci/controller/pci-host-common.c
> +++ b/drivers/pci/controller/pci-host-common.c
> @@ -17,6 +17,27 @@
>  
>  #include "pci-host-common.h"
>  
> +/**
> + * pci_root_ports_have_device - Check if the Root Ports under the Root bus have
> + *				any device underneath
> + * @dev: Root bus
> + *
> + * Return: true if a device is found, false otherwise
> + */
> +bool pci_root_ports_have_device(struct pci_bus *root_bus)
> +{
> +	struct pci_bus *child;
> +
> +	/* Iterate over the Root Port busses and look for any device */
> +	list_for_each_entry(child, &root_bus->children, node) {
> +		if (list_count_nodes(&child->devices))

Is this list ever shrunk? I grepped around and couldn't find where
that happens

Konrad