linux-kernel - Re: [PATCH 4/5] PCI/pwrctrl: Add APIs to power on/off the pwrctrl devices

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Message-ID: <CAMRc=MeRVLALxdPoFP2fXpq+inZpA7h-eCBRuegTkxWUGOpDew@mail.gmail.com>
Date: Tue, 25 Nov 2025 05:34:04 -0800
From: Bartosz Golaszewski <brgl@...ev.pl>
To: manivannan.sadhasivam@....qualcomm.com
Cc: Manivannan Sadhasivam via B4 Relay <devnull+manivannan.sadhasivam.oss.qualcomm.com@...nel.org>, 
	linux-pci@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Chen-Yu Tsai <wens@...nel.org>, 
	Brian Norris <briannorris@...omium.org>, 
	Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>, Niklas Cassel <cassel@...nel.org>, 
	Alex Elder <elder@...cstar.com>, Manivannan Sadhasivam <mani@...nel.org>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Krzysztof Wilczyński <kwilczynski@...nel.org>, 
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>, 
	Bartosz Golaszewski <brgl@...ev.pl>
Subject: Re: [PATCH 4/5] PCI/pwrctrl: Add APIs to power on/off the pwrctrl devices

On Mon, 24 Nov 2025 17:20:47 +0100, Manivannan Sadhasivam via B4 Relay
<devnull+manivannan.sadhasivam.oss.qualcomm.com@...nel.org> said:
> From: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
>
> To fix PCIe bridge resource allocation issues when powering PCIe
> switches with the pwrctrl driver, introduce APIs to explicitly power
> on and off all related devices simultaneously.
>
> Previously, the individual pwrctrl drivers powered on/off the PCIe devices
> autonomously, without any control from the controller drivers. But to
> enforce ordering w.r.t powering on the devices, these APIs will power
> on/off all the devices at the same time.
>
> The pci_pwrctrl_power_on_devices() API recursively scans the PCI child
> nodes, makes sure that pwrctrl drivers are bind to devices, and calls their
> power_on() callbacks.
>
> Similarly, pci_pwrctrl_power_off_devices() API powers off devices
> recursively via their power_off() callbacks.
>
> These APIs are expected to be called during the controller probe and
> suspend/resume time to power on/off the devices. But before calling these
> APIs, the pwrctrl devices should've been created beforehand using the
> pci_pwrctrl_{create/destroy}_devices() APIs.
>
> Co-developed-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
> ---
>  drivers/pci/pwrctrl/core.c  | 121 ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/pci-pwrctrl.h |   4 ++
>  2 files changed, 125 insertions(+)
>
> diff --git a/drivers/pci/pwrctrl/core.c b/drivers/pci/pwrctrl/core.c
> index 6eca54e0d540..e0a0cf015bd0 100644
> --- a/drivers/pci/pwrctrl/core.c
> +++ b/drivers/pci/pwrctrl/core.c
> @@ -65,6 +65,7 @@ void pci_pwrctrl_init(struct pci_pwrctrl *pwrctrl, struct device *dev)
>  {
>  	pwrctrl->dev = dev;
>  	INIT_WORK(&pwrctrl->work, rescan_work_func);
> +	dev_set_drvdata(dev, pwrctrl);
>  }
>  EXPORT_SYMBOL_GPL(pci_pwrctrl_init);
>
> @@ -152,6 +153,126 @@ int devm_pci_pwrctrl_device_set_ready(struct device *dev,
>  }
>  EXPORT_SYMBOL_GPL(devm_pci_pwrctrl_device_set_ready);
>
> +static int __pci_pwrctrl_power_on_device(struct device *dev)

Both this and __pci_pwrctrl_power_off_device() are only used once each. Does
it really make sense to split it out?

> +{
> +	struct pci_pwrctrl *pwrctrl = dev_get_drvdata(dev);
> +
> +	if (!pwrctrl)
> +		return 0;
> +
> +	return pwrctrl->power_on(pwrctrl);
> +}
> +
> +/*
> + * Power on the devices in a depth first manner. Before powering on the device,
> + * make sure its driver is bound.
> + */
> +static int pci_pwrctrl_power_on_device(struct device_node *np)
> +{
> +	struct platform_device *pdev;
> +	int ret;
> +
> +	for_each_available_child_of_node_scoped(np, child) {
> +		ret = pci_pwrctrl_power_on_device(child);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	pdev = of_find_device_by_node(np);
> +	if (pdev) {
> +		if (!device_is_bound(&pdev->dev)) {
> +			dev_err(&pdev->dev, "driver is not bound\n");

This is not an error though, is it? If there are multiple deferalls, we'll
spam the kernel log.

> +			ret = -EPROBE_DEFER;
> +		} else {
> +			ret = __pci_pwrctrl_power_on_device(&pdev->dev);
> +		}
> +		put_device(&pdev->dev);
> +
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;

Bart