Re: [PATCH v4 06/29] bus: Introduce simple-platorm-bus

Andy Shevchenko
2025-10-21T14:07:50Z

On Wed, Oct 15, 2025 at 09:13:53AM +0200, Herve Codina wrote:
> The simple-pm-bus driver handles several simple busses. When it is used
> with busses other than a compatible "simple-pm-bus", it doesn't populate
> its child devices during its probe.
>
> This confuses fw_devlink and results in wrong or missing devlinks.
>
> Once a driver is bound to a device and the probe() has been called,
> device_links_driver_bound() is called.
>
> This function performs operation based on the following assumption:
> If a child firmware node of the bound device is not added as a
> device, it will never be added.
>
> Among operations done on fw_devlinks of those "never be added" devices,
> device_links_driver_bound() changes their supplier.
>
> With devices attached to a simple-bus compatible device, this change
> leads to wrong devlinks where supplier of devices points to the device
> parent (i.e. simple-bus compatible device) instead of the device itself
> (i.e. simple-bus child).
>
> When the device attached to the simple-bus is removed, because devlinks
> are not correct, its consumers are not removed first.
>
> In order to have correct devlinks created, make the simple-bus driver
> compliant with the devlink assumption and create its child devices
> during its probe.
>
> Doing that leads to other issues due to the fact that simple-bus is
> closely related to of_platform_populate().
>
> Indeed, of_platform_populate() can probe child devices if a simple-bus
> compatible node is detected. This behavior is expected by some drivers
> such as some MFD drivers. Those drivers perform some operations in their
> probe() but rely on the core (simple-mfd, simple-bus compatible) to
> populate child devices [1].
>
> Avoiding recursive probing in of_platform_populate() and let the
> simple-bus driver probe its child devices will break some system.
>
> For this reason, keep the current behavior of the simple-bus driver and
> of_platform_populate() as they are and introduce simple-platform-bus
> driver.
>
> This driver doesn't interfere with of_platform_populate() and populates
> child devices during its probe() as expected by fw_devlink.
>
> [1] https://lore.kernel.org/all/20250715095201.1bcb4ab7@bootlin.com/

Link tag?

...

The below is simply wrong. The luck that you got no errors is due to CONFIG_OF
being bool and not tristate in Kconfig. I dunno if this driver ever gets the
'm' capability, but currently it uses tons of dead code (such as MODULE_*()
macros). Disregard of that, the proposed change should go to the separate
compilation unit at bare minimum.

...

> module_platform_driver(simple_pm_bus_driver);

> +module_platform_driver(simple_platform_bus_driver);

^^^ WRONG!

--
With Best Regards,
Andy Shevchenko