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

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Message-Id: <D8PF958QL5AK.2JIE4F1N1NI0F@bootlin.com>
Date: Tue, 25 Mar 2025 15:37:29 +0100
From: "Mathieu Dubois-Briand" <mathieu.dubois-briand@...tlin.com>
To: "Andy Shevchenko" <andriy.shevchenko@...el.com>,
 Uwe Kleine-König <ukleinek@...nel.org>
Cc: "Lee Jones" <lee@...nel.org>, "Rob Herring" <robh@...nel.org>,
 "Krzysztof Kozlowski" <krzk+dt@...nel.org>, "Conor Dooley"
 <conor+dt@...nel.org>, "Kamel Bouhara" <kamel.bouhara@...tlin.com>, "Linus
 Walleij" <linus.walleij@...aro.org>, "Bartosz Golaszewski" <brgl@...ev.pl>,
 "Dmitry Torokhov" <dmitry.torokhov@...il.com>, "Michael Walle"
 <mwalle@...nel.org>, "Mark Brown" <broonie@...nel.org>, "Greg
 Kroah-Hartman" <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
 <rafael@...nel.org>, "Danilo Krummrich" <dakr@...nel.org>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <linux-gpio@...r.kernel.org>, <linux-input@...r.kernel.org>,
 <linux-pwm@...r.kernel.org>, Grégory Clement
 <gregory.clement@...tlin.com>, "Thomas Petazzoni"
 <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v5 04/11] pwm: max7360: Add MAX7360 PWM support

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@...tlin.com 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?

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, 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?

-- 
Mathieu Dubois-Briand, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com