linux-kernel - Re: [PATCH v3 05/28] bus: simple-pm-bus: Populate child nodes at probe

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Message-ID: <20250703093302.4f7743ea@bootlin.com>
Date: Thu, 3 Jul 2025 09:33:02 +0200
From: Herve Codina <herve.codina@...tlin.com>
To: Rob Herring <robh@...nel.org>
Cc: Andrew Lunn <andrew@...n.ch>, Greg Kroah-Hartman
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Subject: Re: [PATCH v3 05/28] bus: simple-pm-bus: Populate child nodes at
 probe

Hi Rob,

On Fri, 27 Jun 2025 10:52:00 -0500
Rob Herring <robh@...nel.org> wrote:

> On Fri, Jun 13, 2025 at 03:47:45PM +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-pm-bus driver
> > compliant with the devlink assumption and create its child devices
> > during its probe.  
> 
> IIRC, skipping child nodes was because there were problems with 
> letting the driver handle 'simple-bus'. How does this avoid that now?

I don't know about the specific issues related to those problems. Do you
have some pointers about them?

> 
> The root of_platform_populate() that created the simple-bus device that 
> gets us to the probe here will continue descending into child nodes. 
> Meanwhile, the probe here is also descending into those same child 
> nodes. Best case, that's just redundant. Worst case, won't you still 
> have the same problem if the first of_platform_populate() creates the 
> devices first?
> 

Maybe we could simply avoid of_platform_populate() to be recursive when a
device populate by of_platform_populate() is one of devices handled by
the simple-bus driver and let the simple-bus driver do the job.

of_platform_populate will handle the first level. It will populate children
of the node given to of_platform_populate() and the children of those
children will be populate by the simple-bus driver.

I could try a modification in that way. Do you think it could be a correct
solution?

Best regards,
Hervé