linux-kernel - Re: [PATCH v2 05/26] bus: simple-pm-bus: Populate child nodes at probe

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Message-ID: <20250519135818.01db3341@bootlin.com>
Date: Mon, 19 May 2025 13:58:18 +0200
From: Herve Codina <herve.codina@...tlin.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Andrew Lunn <andrew@...n.ch>, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, "Rafael J. Wysocki" <rafael@...nel.org>,
 Danilo Krummrich <dakr@...nel.org>, Shawn Guo <shawnguo@...nel.org>, Sascha
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 Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v2 05/26] bus: simple-pm-bus: Populate child nodes at
 probe

Hi Andy,

On Thu, 8 May 2025 17:27:52 +0300
Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:

> On Wed, May 07, 2025 at 09:12:47AM +0200, Herve Codina wrote:
> > The simple-pm-bus drivers handles several simple bus. When it is used  
> 
> bus --> busses ?

Yes sure.

> 
> > with busses other than a compatible "simple-pm-bus", it don'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.  
> 
> ...
> 
> >  	if (match && match->data) {
> >  		if (of_property_match_string(np, "compatible", match->compatible) == 0)  
> 
> Side note, there is an fwnode_is_device_compatible() API for such cases. And IIRC
> there is also OF variant of it.

fwnode_device_is_compatible() checked for all compatible string. I mean, if
we have compatible = "foo,custom-bus", "simple-bus";
fwnode_device_is_compatible() checking against "simple-bus" returns true.

Here, we want "simple-bus" as the first position in the compatible string.
In other word, we want to match the more specific compatible string as
mentioned in the comment.

> 
> > -			return 0;
> > +			goto populate;
> >  		else
> >  			return -ENODEV;
> >  	}  
> 
> ...
> 
> > +	if (pdev->dev.of_node)  
> 
> Why do you need this check? AFAICS it dups the one the call has already in it.

of_platform_populate() was called only if an OF node is present.
I want to call of_platform_depopulate() on removal also only if an OF node
is present.

I don't see the other call that duplicated this check.

Can you clarify?

> 
> > +		of_platform_depopulate(&pdev->dev);  
> 

Best regards,
Hervé