On Fri, Jul 11, 2025 at 05:43:33PM GMT, Brian Norris wrote:
> From: Brian Norris <briannorris@xxxxxxxxxx>
>
> We have asymmetry w.r.t. pwrctrl device creation and destruction.
> pwrctrl devices are created by the host bridge, as part of scanning for
> child devices, but they are destroyed by the child device. This causes
> confusing behavior in cases like the following:
>
> 1. PCI device is removed (e.g., via /sys/bus/pci/devices/*/remove);
> pwrctrl device is also destroyed
> 2. pwrctrl driver is removed (e.g., rmmod)
> 3. pwrctrl driver is reloaded
>
> One could expect #3 to re-bind to the pwrctrl device and re-power the
> device; but there's no device to bind to, so it remains off. Instead, we
> require a forced rescan (/sys/bus/pci/devices/*/rescan) to recreate the
> pwrctrl device(s) and restore power.
>
> This asymmetry isn't required though; it makes more logical sense to
> retain the pwrctrl devices even without the PCI device, since pwrctrl is
> more of a logical ancestor than a child.
>
> Additionally, Documentation/PCI/sysfs-pci.rst documents the behavior of
> step #1 (remove):
>
> The 'remove' file is used to remove the PCI device, by writing a
> non-zero integer to the file. This does not involve any kind of
> hot-plug functionality, e.g. powering off the device.
>
> Instead, let's destroy a pwrctrl device only when its parent (the host
> bridge) is destroyed.
>
Sounds good to me!
> We use of_platform_device_destroy(), since it's the logical inverse of
> pwrctrl creation (of_platform_device_create()). It performs more or less
> the same things pci_pwrctrl_unregister() did, with some added bonus of
> ensuring these are OF_POPULATED devices.
>
If you take a look at commit f1536585588b ("PCI: Don't rely on
of_platform_depopulate() for reused OF-nodes"), you can realize that the PCI
core clears OF_POPULATED flag while removing the PCI device. So
of_platform_device_destroy() will do nothing.
- Mani
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