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Date: Tue, 28 May 2024 21:08:20 +0300
From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Rob Herring <robh@kernel.org>
Cc: Krzysztof Kozlowski <krzk@kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= <ukleinek@kernel.org>,
	linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
	linux-gpio@vger.kernel.org, linux-pwm@vger.kernel.org,
	Alexandru Ardelean <alexandru.ardelean@analog.com>,
	Bartosz Golaszewski <brgl@bgdev.pl>,
	Conor Dooley <conor+dt@kernel.org>,
	Krzysztof Kozlowski <krzk+dt@kernel.org>,
	Lee Jones <lee@kernel.org>, Saravana Kannan <saravanak@google.com>
Subject: Re: [PATCH 2/5] dt-bindings: Add bindings for the Analog Devices
 ADP5585
Message-ID: <20240528180820.GE29970@pendragon.ideasonboard.com>
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In-Reply-To: <20240528151251.GA155664-robh@kernel.org>

Hi Rob,

On Tue, May 28, 2024 at 10:12:51AM -0500, Rob Herring wrote:
> On Fri, May 24, 2024 at 02:16:41AM +0300, Laurent Pinchart wrote:
> > Hi Krzysztof,
> > 
> > (There's a question for the GPIO and PWM maintainers below)
> > 
> > On Wed, May 22, 2024 at 09:40:02AM +0200, Krzysztof Kozlowski wrote:
> > > On 22/05/2024 09:22, Laurent Pinchart wrote:
> > > > On Wed, May 22, 2024 at 08:57:56AM +0200, Krzysztof Kozlowski wrote:
> > > >> On 21/05/2024 21:43, Laurent Pinchart wrote:
> > > >>> On Tue, May 21, 2024 at 09:05:50PM +0200, Krzysztof Kozlowski wrote:
> > > >>>> On 20/05/2024 21:59, Laurent Pinchart wrote:
> > > >>>>> The ADP5585 is a 10/11 input/output port expander with a built in keypad
> > > >>>>> matrix decoder, programmable logic, reset generator, and PWM generator.
> > > >>>>> These bindings model the device as an MFD, and support the GPIO expander
> > > >>>>> and PWM functions.
> > > >>>>>
> > > >>>>> These bindings support the GPIO and PWM functions.
> > > >>>>>
> > > >>>>> Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > >>>>> ---
> > > >>>>> I've limited the bindings to GPIO and PWM as I lack hardware to design,
> > > >>>>> implement and test the rest of the features the chip supports.
> > > >>>>> ---
> > > >>>>>  .../bindings/gpio/adi,adp5585-gpio.yaml       |  36 ++++++
> > > >>>>>  .../devicetree/bindings/mfd/adi,adp5585.yaml  | 117 ++++++++++++++++++
> > > >>>>>  .../bindings/pwm/adi,adp5585-pwm.yaml         |  35 ++++++
> > > >>>>>  MAINTAINERS                                   |   7 ++
> > > >>>>>  4 files changed, 195 insertions(+)
> > > >>>>>  create mode 100644 Documentation/devicetree/bindings/gpio/adi,adp5585-gpio.yaml
> > > >>>>>  create mode 100644 Documentation/devicetree/bindings/mfd/adi,adp5585.yaml
> > > >>>>>  create mode 100644 Documentation/devicetree/bindings/pwm/adi,adp5585-pwm.yaml
> > > >>>>>
> > > >>>>> diff --git a/Documentation/devicetree/bindings/gpio/adi,adp5585-gpio.yaml b/Documentation/devicetree/bindings/gpio/adi,adp5585-gpio.yaml
> > > >>>>> new file mode 100644
> > > >>>>> index 000000000000..210e4d53e764
> > > >>>>> --- /dev/null
> > > >>>>> +++ b/Documentation/devicetree/bindings/gpio/adi,adp5585-gpio.yaml
> > > >>>>> @@ -0,0 +1,36 @@
> > > >>>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > >>>>> +%YAML 1.2
> > > >>>>> +---
> > > >>>>> +$id: http://devicetree.org/schemas/gpio/adi,adp5585-gpio.yaml#
> > > >>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > >>>>> +
> > > >>>>> +title: Analog Devices ADP5585 GPIO Expander
> > > >>>>> +
> > > >>>>> +maintainers:
> > > >>>>> +  - Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > >>>>> +
> > > >>>>> +description: |
> > > >>>>> +  The Analog Devices ADP5585 has up to 11 GPIOs represented by a "gpio" child
> > > >>>>> +  node of the parent MFD device. See
> > > >>>>> +  Documentation/devicetree/bindings/mfd/adi,adp5585.yaml for further details as
> > > >>>>> +  well as an example.
> > > >>>>> +
> > > >>>>> +properties:
> > > >>>>> +  compatible:
> > > >>>>> +    const: adi,adp5585-gpio
> > > >>>>> +
> > > >>>>> +  gpio-controller: true
> > > >>>>> +
> > > >>>>> +  '#gpio-cells':
> > > >>>>> +    const: 2
> > > >>>>> +
> > > >>>>> +  gpio-reserved-ranges: true
> > > >>>>
> > > >>>> There are no resources here, so new compatible is not really warranted.
> > > >>>> Squash the node into parent.
> > > >>>
> > > >>> Child nodes seem (to me) to be the standard way to model functions in
> > > >>> MFD devices. Looking at mfd_add_device(), for OF-based systems, the
> > > >>> function iterates over child nodes. I don't mind going a different
> > > >>
> > > >> Only to assign of node, which could be skipped as well.
> > > > 
> > > > It has to be assigned somehow, otherwise the GPIO and PWM lookups won't
> > > > work. That doesn't have to be done in mfd_add_device() though, it can
> > > > also be done manually by the driver. Looking at the example you gave,
> > > > cs42l43_pin_probe() handles that assignment. I would have considered
> > > > that a bit of a hack, but if that's your preferred approach, I'm fine
> > > > with it. Could you confirm you're OK with that ?
> > > 
> > > I am fine with the drivers doing that. It's not a hack, for all
> > > sub-devices (e.g. also auxiliary bus) you won't have automatic of_node
> > > assignment.
> > 
> > I gave this a try, and here's what I came up with to drop the compatible
> > string. Please ignore for a moment the fact that the child nodes are
> > still there, that's an orthogonal question which I can address
> > separately. What I would like is feedback on how the OF nodes are
> > handled.
> > 
> > diff --git a/drivers/gpio/gpio-adp5585.c b/drivers/gpio/gpio-adp5585.c
> > index 9696a4cdcfc1..8480ceef05ce 100644
> > --- a/drivers/gpio/gpio-adp5585.c
> > +++ b/drivers/gpio/gpio-adp5585.c
> > @@ -174,6 +174,7 @@ static int adp5585_gpio_probe(struct platform_device *pdev)
> >  	struct adp5585_dev *adp5585 = dev_get_drvdata(pdev->dev.parent);
> >  	struct adp5585_gpio_dev *adp5585_gpio;
> >  	struct device *dev = &pdev->dev;
> > +	struct device_node *node;
> >  	struct gpio_chip *gc;
> >  	int ret;
> > 
> > @@ -187,6 +188,13 @@ static int adp5585_gpio_probe(struct platform_device *pdev)
> > 
> >  	mutex_init(&adp5585_gpio->lock);
> > 
> > +	node = of_get_child_by_name(dev->parent->of_node, "gpio");
> > +	if (!node)
> > +		return dev_err_probe(dev, -ENXIO, "'gpio' child node not found\n");
> > +
> > +	dev->of_node = node;
> > +	dev->fwnode = &node->fwnode;
> 
> Use device_set_of_node_from_dev().

That only works without child nodes in DT. Here I'm assigning the gpio
child node, not the node of the parent device.

> > +
> >  	gc = &adp5585_gpio->gpio_chip;
> >  	gc->parent = dev;
> >  	gc->direction_input = adp5585_gpio_direction_input;
> > @@ -204,6 +212,9 @@ static int adp5585_gpio_probe(struct platform_device *pdev)
> >  	ret = devm_gpiochip_add_data(&pdev->dev, &adp5585_gpio->gpio_chip,
> >  				     adp5585_gpio);
> >  	if (ret) {
> > +		of_node_put(dev->of_node);
> > +		dev->of_node = NULL;
> > +		dev->fwnode = NULL;
> >  		mutex_destroy(&adp5585_gpio->lock);
> >  		return dev_err_probe(&pdev->dev, ret, "failed to add GPIO chip\n");
> >  	}
> > @@ -215,6 +226,10 @@ static void adp5585_gpio_remove(struct platform_device *pdev)
> >  {
> >  	struct adp5585_gpio_dev *adp5585_gpio = platform_get_drvdata(pdev);
> > 
> > +	of_node_put(pdev->dev.of_node);
> > +	pdev->dev.of_node = NULL;
> > +	pdev->dev.fwnode = NULL;
> > +
> >  	mutex_destroy(&adp5585_gpio->lock);
> >  }
> > 
> > diff --git a/drivers/pwm/pwm-adp5585.c b/drivers/pwm/pwm-adp5585.c
> > index e39a6ea5f794..3b190567ea0b 100644
> > --- a/drivers/pwm/pwm-adp5585.c
> > +++ b/drivers/pwm/pwm-adp5585.c
> > @@ -146,6 +146,8 @@ static const struct pwm_ops adp5585_pwm_ops = {
> >  static int adp5585_pwm_probe(struct platform_device *pdev)
> >  {
> >  	struct adp5585_dev *adp5585 = dev_get_drvdata(pdev->dev.parent);
> > +	struct device *dev = &pdev->dev;
> > +	struct device_node *node;
> >  	struct pwm_chip *chip;
> >  	int ret;
> > 
> > @@ -153,16 +155,34 @@ static int adp5585_pwm_probe(struct platform_device *pdev)
> >  	if (IS_ERR(chip))
> >  		return PTR_ERR(chip);
> > 
> > +	node = of_get_child_by_name(dev->parent->of_node, "pwm");
> > +	if (!node)
> > +		return dev_err_probe(dev, -ENXIO, "'pwm' child node not found\n");
> > +
> > +	dev->of_node = node;
> > +	dev->fwnode = &node->fwnode;
> > +
> >  	pwmchip_set_drvdata(chip, adp5585->regmap);
> >  	chip->ops = &adp5585_pwm_ops;
> > 
> >  	ret = devm_pwmchip_add(&pdev->dev, chip);
> > -	if (ret)
> > +	if (ret) {
> > +		of_node_put(dev->of_node);
> > +		dev->of_node = NULL;
> > +		dev->fwnode = NULL;
> >  		return dev_err_probe(&pdev->dev, ret, "failed to add PWM chip\n");
> > +	}
> > 
> >  	return 0;
> >  }
> > 
> > +static void adp5585_pwm_remove(struct platform_device *pdev)
> > +{
> > +	of_node_put(pdev->dev.of_node);
> 
> Wouldn't the driver core do this already? It's not going to know how or 
> when of_node was set, so should be doing a put regardless.

It does, but only when the struct device is being destroyed. Unbinding
and rebinding would leak a reference. Using
device_set_of_node_from_dev() solves that problem, but doesn't work with
child nodes.

I'm going to send a v2 that squashes everything in a single DT node,
which allows usage of device_set_of_node_from_dev(). Let's see if it
will be more palatable.

> > +	pdev->dev.of_node = NULL;
> > +	pdev->dev.fwnode = NULL;
> > +}
> > +
> >  static struct platform_driver adp5585_pwm_driver = {
> >  	.driver	= {
> >  		.name = "adp5585-pwm",
> > 
> > Is this acceptable ? I'm a bit concerned about poking the internals of
> > struct device directly from drivers.
> > 
> > I have also refrained from setting fnode->dev to point back to the
> > device as fone by cs42l43_pin_probe(), as a comment in struct
> > fwnode_handle indicates that the dev field is for device links only and
> > shouldn't be touched by anything else. I'm not sure if I should set it.
> 
> I think no, but best for Saravana to comment.
> 
> > > >>> routes, could you indicate what you have in mind, perhaps pointing to an
> > > >>> existing driver as an example ?
> > > >>
> > > >> Most of them? OK, let's take the last added driver in MFD directory:
> > > >> cirrus,cs42l43
> > > >> It has three children and only two nodes, because only these two devices
> > > >> actually need/use/benefit the subnodes.
> > > > 
> > > > Still trying to understand what bothers you here, is it the child nodes,
> > > > or the fact that they have a compatible string and are documented in a
> > > > separate binding ? Looking at the cirrus,cs42l43 bindings and the
> > > 
> > > What bothers me (and as expressed in many reviews by us) is representing
> > > driver structure directly in DT. People model DT based how their Linux
> > > drivers are represented. I don't care about driver stuff here, but DT/DTS.
> > 
> > DT models the hardware as seen from a software point of view. 
> 
> True, but it's for all software's PoV, not some specific s/w.

Agreed.

> > It
> > shouldn't reflect the structure of Linux drivers, but it has to be
> > usable by drivers.
> 
> Either way is usable.

-- 
Regards,

Laurent Pinchart