linux-kernel - Re: [PATCH v2 3/4] gpio: adp5585: Add Analog Devices ADP5585 support

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Date: Wed, 29 May 2024 17:24:03 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-gpio@...r.kernel.org, linux-pwm@...r.kernel.org, 
	Bartosz Golaszewski <brgl@...ev.pl>, Conor Dooley <conor+dt@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Lee Jones <lee@...nel.org>, 
	Linus Walleij <linus.walleij@...aro.org>, Rob Herring <robh@...nel.org>, 
	Uwe Kleine-König <ukleinek@...nel.org>, 
	Haibo Chen <haibo.chen@....com>
Subject: Re: [PATCH v2 3/4] gpio: adp5585: Add Analog Devices ADP5585 support

On Wed, May 29, 2024 at 12:48 PM Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> On Wed, May 29, 2024 at 09:16:43AM +0300, Andy Shevchenko wrote:
> > On Tue, May 28, 2024 at 11:20 PM Laurent Pinchart wrote:
> > > On Tue, May 28, 2024 at 10:36:06PM +0300, Andy Shevchenko wrote:

..

> > > > > +   device_set_of_node_from_dev(dev, dev->parent);
> > > >
> > > > Why not device_set_node()?
> > >
> > > Because device_set_of_node_from_dev() is meant for this exact use case,
> > > where the same node is used for multiple devices. It also puts any
> > > previous dev->of_node, ensuring proper refcounting when devices are
> > > unbound and rebound, without being deleted.
> >
> > When will the refcount be dropped (in case of removal of this device)?
> > Or you mean it shouldn't?
>
> Any refcount taken on the OF node needs to be dropped. The device core
> only drops the refcount when the device is being deleted, not when
> there's an unbind-rebind cycle without deletion of the device (as
> happens for instance when the module is unloaded and reloaded).

Under "device" you meant the real hardware, as Linux device (instance
of the struct device object) is being rebuilt AFAIK)?

> This has
> to be handled by the driver. device_set_of_node_from_dev() handles it.

But why do you need to keep a parent node reference bumped?
Only very few drivers in the kernel use this API and I believe either
nobody knows what they are doing and you are right, or you are doing
something which is not needed.

--
With Best Regards,
Andy Shevchenko