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: <8dfd167b-246f-446c-bd86-ea9de95e445c@intel.com>
Date: Wed, 4 Feb 2026 20:27:54 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: Frank Li <Frank.li@....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 04/02/2026 18:06, Frank Li wrote:
> 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.

In face it is not necessary because the driver is no longer using
auto-suspend.  I will take it out.