linux-kernel - Re: [PATCH v5 2/5] mfd: Add support for the Lantiq PEF2256 framer

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Date:   Wed, 5 Apr 2023 18:00:23 +0200
From:   Herve Codina <herve.codina@...tlin.com>
To:     Lee Jones <lee@...nel.org>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, alsa-devel@...a-project.org,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v5 2/5] mfd: Add support for the Lantiq PEF2256 framer

Hi Lee,
On Wed, 5 Apr 2023 14:54:50 +0100
Lee Jones <lee@...nel.org> wrote:

> On Tue, 04 Apr 2023, Krzysztof Kozlowski wrote:
> 
> > On 04/04/2023 10:07, Herve Codina wrote:
> >  
> > >>> So, the structure I have in mind:
> > >>> - pef2256.c (MFD)
> > >>>   implement and do the setup at probe()
> > >>>   Add the children at probe():
> > >>>     - pef2256-pinctrl (pinctrl) added using mfd_add_devices()
> > >>>     - pef2256-codec (ASoC codec) added using devm_of_platform_populate()
> > >>>
> > >>> Lee, with this in mind, can the core pef2256.c be a MFD driver ?  
> > >>
> > >> You do not use MFD here, so why do you want to keep it in MFD? If you
> > >> disagree, please tell me where is the MFD code in your patch?  
> > >
> > > I don't want to absolutely use MFD.
> > > I just want to put my driver somewhere and I don't know the right location
> > > between MFD and Misc.
> > >
> > > Basically, the driver needs to do (little simplified and error path removed):
> > >
> > >   static const struct mfd_cell pef2256_devs[] = {
> > >   	{ .name = "lantiq-pef2256-pinctrl", },
> > >   };
> > >
> > >   static int pef2256_probe(struct platform_device *pdev)
> > >   {
> > > 	struct pef2256 *pef2256;
> > > 	void __iomem *iomem;
> > > 	int ret;
> > > 	int irq;
> > >
> > > 	pef2256 = devm_kzalloc(&pdev->dev, sizeof(*pef2256), GFP_KERNEL);
> > > 	if (!pef2256)
> > > 		return -ENOMEM;
> > >
> > > 	pef2256->dev = &pdev->dev;
> > >
> > > 	iomem = devm_platform_ioremap_resource(pdev, 0);
> > >
> > > 	pef2256->regmap = devm_regmap_init_mmio(&pdev->dev, iomem,
> > > 						&pef2256_regmap_config);
> > >
> > > 	pef2256->mclk = devm_clk_get_enabled(&pdev->dev, "mclk");
> > > 	pef2256->sclkr = devm_clk_get_enabled(&pdev->dev, "sclkr");
> > > 	pef2256->sclkx = devm_clk_get_enabled(&pdev->dev, "sclkx");
> > >
> > > 	pef2256->reset_gpio = devm_gpiod_get_optional(&pdev->dev, "reset", GPIOD_OUT_LOW);
> > > 	if (pef2256->reset_gpio) {
> > > 		gpiod_set_value_cansleep(pef2256->reset_gpio, 1);
> > > 		udelay(10);
> > > 		gpiod_set_value_cansleep(pef2256->reset_gpio, 0);
> > > 		udelay(10);
> > > 	}
> > >
> > > 	pef2556_of_parse(pef2256, np);
> > >
> > > 	irq = platform_get_irq(pdev, 0);
> > > 	ret = devm_request_irq(pef2256->dev, irq, pef2256_irq_handler, 0, "pef2256", pef2256);
> > >
> > > 	platform_set_drvdata(pdev, pef2256);
> > >
> > > 	mfd_add_devices(pef2256->dev, PLATFORM_DEVID_NONE, pef2256_devs,
> > > 	      		ARRAY_SIZE(pef2256_devs), NULL, 0, NULL);  
> >
> > Wait, now you use MFD framework, so the driver is suitable for MFD.
> > Before there was nothing like that in your code.  
> 
> Agree, the above is suitable for MFD, since it does all the things I
> said your last one did not.  You *can* also use of_platform_populate()
> here, since you are *also* requesting and initialising shared resources.
> You cannot do *both* however.
> 

Thanks for having confirmed that this driver can be a MFD driver.

Related to of_platform_populate() / mfd_add_devices(), I wanted to use both
because:
- the pinctrl part does not have (and does not need to have) a specific node
  with a specific compatible property. In order to instantiate the related
  driver mfd_add_devices() is the only way I know.
- the audio component nodes have a compatible string and several components
  (ie several nodes) can be present. of_platform_populate() call seems the
  simple way to instantiate them.

Is there a way to use mfd_add_devices() in this case without the need to
count the audio component nodes in order to allocate as much mfd_cell as
nodes having a matching compatible property ? Is there an other API to do
it ?

Best regards,
Hervé