linux-kernel - Re: [PATCH V2 5/6] i3c: mipi-i3c-hci-pci: Add optional ability to manage child runtime PM

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Message-ID: <aYNumA0-FvE-g7nl@lizhi-Precision-Tower-5810>
Date: Wed, 4 Feb 2026 11:06:48 -0500
From: Frank Li <Frank.li@....com>
To: Adrian Hunter <adrian.hunter@...el.com>
Cc: alexandre.belloni@...tlin.com, rafael@...nel.org,
	linux-i3c@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [PATCH V2 5/6] i3c: mipi-i3c-hci-pci: Add optional ability to
 manage child runtime PM

On Wed, Feb 04, 2026 at 01:15:10PM +0200, Adrian Hunter wrote:
> Some platforms implement the MIPI I3C HCI Multi-Bus Instance capability,
> where a single parent device hosts multiple I3C controller instances.  In
> such designs, the parent - not the individual child instances - may need to
> coordinate runtime PM so that all controllers runtime PM callbacks are
> invoked in a controlled and synchronized manner.
>
> For example, if the parent enables IBI-wakeup when transitioning into a
> low-power state, every bus instance must remain able to receive IBIs up
> until that point.  This requires deferring the individual controllers'
> runtime suspend callbacks (which disable bus activity) until the parent
> decides it is safe for all instances to suspend together.
>
> To support this usage model:
>
>   * Add runtime PM and system PM callbacks in the PCI driver to invoke
>     the mipi-i3c-hci driver's runtime PM callbacks for each instance.
>
>   * Introduce a driver-data flag, control_instance_pm, which opts into
>     the new parent-managed PM behaviour.
>
>   * Ensure the callbacks are only used when the corresponding instance is
>     operational at suspend time.  This is reliable because the operational
>     state cannot change while the parent device is undergoing a PM
>     transition, and PCI always performs a runtime resume before system
>     suspend on current configurations, so that suspend and resume alternate
>     irrespective of whether it is runtime or system PM.
>
> By that means, parent-managed runtime PM coordination for multi-instance
> MIPI I3C HCI PCI devices is provided without altering existing behaviour on
> platforms that do not require it.
>
> Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
> ---
...
> +
> +static int mipi_i3c_hci_pci_suspend(struct device *dev)
> +{
> +	struct mipi_i3c_hci_pci *hci = dev_get_drvdata(dev);
> +	struct mipi_i3c_hci_pci_pm_data pm_data = {};
> +	int ret;
> +
> +	if (!hci->info->control_instance_pm)
> +		return 0;
> +
> +	ret = device_for_each_child_reverse(dev, &pm_data, mipi_i3c_hci_pci_suspend_instance);
> +	if (ret) {
> +		if (ret == -EAGAIN || ret == -EBUSY)
> +			pm_runtime_mark_last_busy(&hci->pci->dev);

This should not neccessary, the runtime suspend API already call it now.

Frank

> +		for (int i = 0; i < pm_data.dev_cnt; i++)
> +			i3c_hci_rpm_resume(pm_data.dev[i]);
> +	}
> +
> +	return ret;
> +}
> +
> +static int mipi_i3c_hci_pci_resume(struct device *dev)
> +{
> +	struct mipi_i3c_hci_pci *hci = dev_get_drvdata(dev);
> +	struct mipi_i3c_hci_pci_pm_data pm_data = {};
> +	int ret;
> +
> +	if (!hci->info->control_instance_pm)
> +		return 0;
> +
> +	ret = device_for_each_child(dev, &pm_data, mipi_i3c_hci_pci_resume_instance);
> +	if (ret)
> +		for (int i = 0; i < pm_data.dev_cnt; i++)
> +			i3c_hci_rpm_suspend(pm_data.dev[i]);
> +
> +	return ret;
> +}
> +
>  static void mipi_i3c_hci_pci_rpm_allow(struct device *dev)
>  {
>  	pm_runtime_put(dev);
> @@ -323,6 +455,8 @@ static void mipi_i3c_hci_pci_remove(struct pci_dev *pci)
>
>  /* PM ops must exist for PCI to put a device to a low power state */
>  static const struct dev_pm_ops mipi_i3c_hci_pci_pm_ops = {
> +	RUNTIME_PM_OPS(mipi_i3c_hci_pci_suspend, mipi_i3c_hci_pci_resume, NULL)
> +	SYSTEM_SLEEP_PM_OPS(mipi_i3c_hci_pci_suspend, mipi_i3c_hci_pci_resume)
>  };
>
>  static const struct pci_device_id mipi_i3c_hci_pci_devices[] = {
> --
> 2.51.0
>