Re: [PATCH v5 04/11] pwm: max7360: Add MAX7360 PWM support

[Andy Shevchenko]

On Tue, Mar 25, 2025 at 03:37:29PM +0100, Mathieu Dubois-Briand wrote:
> On Thu Mar 20, 2025 at 11:48 AM CET, Andy Shevchenko wrote:
> > On Thu, Mar 20, 2025 at 08:50:00AM +0100, Uwe Kleine-König wrote:
> > > On Wed, Mar 19, 2025 at 01:18:50PM +0200, Andy Shevchenko wrote:
> > > > On Tue, Mar 18, 2025 at 05:26:20PM +0100, mathieu.dubois-briand@xxxxxxxxxxx wrote:

...

> > > > > +	chip = devm_pwmchip_alloc(dev->parent, MAX7360_NUM_PWMS, 0);
> > > > 
> > > > This is quite worrying. The devm_ to parent makes a lot of assumptions that may
> > > > not be realised. If you really need this, it has to have a very good comment
> > > > explaining why and object lifetimes.
> > > 
> > > Pretty sure this is broken. This results for example in the device link
> > > being created on the parent. So if the pwm devices goes away a consumer
> > > might not notice (at least in the usual way). I guess this was done to
> > > ensure that #pwm-cells is parsed from the right dt node? If so, that
> > > needs a different adaption. That will probably involve calling
> > > device_set_of_node_from_dev().
> >
> > It's an MFD based driver, and MFD core cares about propagating fwnode by
> > default. I believe it should just work if we drop that '->parent' part.
> 
> Are you sure about that?

Yes and no. If your DT looks like (pseudo code as I don't know
DTS syntax by heart):

	device: {
		parent-property = value;
		child0:
			...
		child1:
			...
	}

the parent-property value is automatically accessible via fwnode API,
but I don't know what will happen to the cases when each of the children
has its own compatible string. This might be your case, but again,
I'm not an expert in DT.

> On my side it does not work if I just drop the '->parent', this is why I
> ended whit this (bad) pattern.

> Now it does work if I do call device_set_of_node_from_dev() manually,

AFAICT, this is wrong API to be called in the children. Are you talking about
parent code?

> so it's definitely better. But I believe the MFD core is not propagating
> OF data, and I did not find where it would do that in the code. Yet it
> does something like this for ACPI in mfd_acpi_add_device(). Or maybe we
> do something bad in our MFD driver?

...or MFD needs something to have... Dunno.

-- 
With Best Regards,
Andy Shevchenko