linux-kernel - Re: [PATCH v2 1/3] PCI: host-common: Add an API to check for any device under the Root Ports

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Message-ID: <aRIUktA5ZZhqj1GA@lizhi-Precision-Tower-5810>
Date: Mon, 10 Nov 2025 11:36:34 -0500
From: Frank Li <Frank.li@....com>
To: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
Cc: lpieralisi@...nel.org, kwilczynski@...nel.org, mani@...nel.org,
	bhelgaas@...gle.com, 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,
	vincent.guittot@...aro.org
Subject: Re: [PATCH v2 1/3] PCI: host-common: Add an API to check for any
 device under the Root Ports

On Fri, Nov 07, 2025 at 10:13:17AM +0530, 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>

Reviewed-by: Frank Li <Frank.Li@....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..772bac8b3bf2 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
> + * @root_bus: Root bus to check for
> + *
> + * 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_empty(&child->devices))
> +			return true;
> +	}
> +
> +	return false;
> +}
> +EXPORT_SYMBOL_GPL(pci_root_ports_have_device);
> +
>  static void gen_pci_unmap_cfg(void *ptr)
>  {
>  	pci_ecam_free((struct pci_config_window *)ptr);
> diff --git a/drivers/pci/controller/pci-host-common.h b/drivers/pci/controller/pci-host-common.h
> index 51c35ec0cf37..ff1c2ff98043 100644
> --- a/drivers/pci/controller/pci-host-common.h
> +++ b/drivers/pci/controller/pci-host-common.h
> @@ -19,4 +19,6 @@ void pci_host_common_remove(struct platform_device *pdev);
>
>  struct pci_config_window *pci_host_common_ecam_create(struct device *dev,
>  	struct pci_host_bridge *bridge, const struct pci_ecam_ops *ops);
> +
> +bool pci_root_ports_have_device(struct pci_bus *root_bus);
>  #endif
> --
> 2.48.1
>