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Date:   Tue, 11 Apr 2023 18:16:40 +0200
From:   Herve Codina <herve.codina@bootlin.com>
To:     Lee Jones <lee@kernel.org>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Liam Girdwood <lgirdwood@gmail.com>,
        Mark Brown <broonie@kernel.org>,
        Jaroslav Kysela <perex@perex.cz>,
        Takashi Iwai <tiwai@suse.com>, linux-kernel@vger.kernel.org,
        devicetree@vger.kernel.org, alsa-devel@alsa-project.org,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Subject: Re: [PATCH v5 2/5] mfd: Add support for the Lantiq PEF2256 framer
Message-ID: <20230411181640.50c19d4e@bootlin.com>
In-Reply-To: <20230405180023.4aebaa08@bootlin.com>
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 <20230331141104.42445da9@bootlin.com>
 <a642e653-e3e2-c3d2-68cb-1efc92be05bb@linaro.org>
 <20230331165904.4e7f46a1@bootlin.com>
 <20230403142822.GA8371@google.com>
 <20230404092036.2d1cd5d9@bootlin.com>
 <f7ab2fcc-93fc-ce87-8767-579d33907225@linaro.org>
 <20230404100759.5bc9cd20@bootlin.com>
 <143754c2-9e37-4386-af92-174c0df2eb0a@linaro.org>
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Hi Lee,

On Wed, 5 Apr 2023 18:00:23 +0200
Herve Codina <herve.codina@bootlin.com> wrote:

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

I looked deeper for using mfd_add_devices() only and found an issue (related
to my use-case).

mfd_add_devices() calls mfd_add_device() and in this function we have:
---- 8< ----
	if (IS_ENABLED(CONFIG_OF) && parent->of_node && cell->of_compatible) {
		for_each_child_of_node(parent->of_node, np) {
			if (of_device_is_compatible(np, cell->of_compatible)) {
				/* Ignore 'disabled' devices error free */
				if (!of_device_is_available(np)) {
					of_node_put(np);
					ret = 0;
					goto fail_alias;
				}

				ret = mfd_match_of_node_to_dev(pdev, np, cell);
				if (ret == -EAGAIN)
					continue;
				of_node_put(np);
				if (ret)
					goto fail_alias;

				break;
			}
		}

		if (!pdev->dev.of_node)
			pr_warn("%s: Failed to locate of_node [id: %d]\n",
				cell->name, platform_id);
	}
---- 8< ----

My issue is related to the loop.
The loop is aborted if the device is not available (typically 'Disabled' in the
DT node).

My full pef2256 node can have several pef2256 audio subnodes with compatible
set to "lantiq,pef2256-codec" and some of them can have 'status = "Disabled";'
As soon as one device (with my expected compatible) is found 'Disabled', there
is no way to look at other children.

Having 'continue' in case of device not available in the loop to look at the
next child will change the behavior of mfd_add_device().
Do you think that looking at next child if we find a 'not available' child
can be correct for mfd_add_device() ?
This probably will have impacts on other MFD drivers.

Best regards,
Hervé