linux-kernel - Re: [PATCH RFT/RFC] mfd: cs42l43: setup true links with software nodes

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Message-ID: <aR2OU4se7lxcMtGW@opensource.cirrus.com>
Date: Wed, 19 Nov 2025 09:30:59 +0000
From: Charles Keepax <ckeepax@...nsource.cirrus.com>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: David Rhodes <david.rhodes@...rus.com>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>,
        Lee Jones <lee@...nel.org>, Mark Brown <broonie@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Maciej Strozek <mstrozek@...nsource.cirrus.com>,
        Andy Shevchenko <andy@...nel.org>, linux-sound@...r.kernel.org,
        patches@...nsource.cirrus.com, linux-kernel@...r.kernel.org,
        linux-spi@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH RFT/RFC] mfd: cs42l43: setup true links with software
 nodes

On Wed, Nov 19, 2025 at 10:10:24AM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> 
> Currently the SPI driver sets up a software node rerefencing the GPIO
> controller exposing the chip-select GPIO but this node never gets
> attached to the actual GPIO provider. The lookup uses the weird way GPIO
> core performs the software node lookup by the swnode's name. We want to
> switch to a true firmware node lookup so the actual link must exist.
> Move the configuration to the MFD core and connect the SPI and pinctrl
> sub-devices with software node references.
> 
> Fixes: 439fbc97502a ("spi: cs42l43: Add bridged cs35l56 amplifiers")
> Reported-by: Charles Keepax <ckeepax@...nsource.cirrus.com>
> Closes: https://lore.kernel.org/all/aRyf7qDdHKABppP8@opensource.cirrus.com/
> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> ---
> Hi Charles!
> 
> Please give this a try. It's only build-tested so far. I hope I
> understood correctly that it's the SPI driver that needs the "cs" GPIO
> from the pinctrl.

Unfortunately it fails with an -EBUSY on adding the MFD children.
I will investigate a little more and report back.

> +static const struct software_node cs42l43_gpiochip_swnode = {
> +	.name = "cs42l43-pinctrl",
> +};
> +
> +static const struct property_entry cs42l43_cs_props[] = {
> +	PROPERTY_ENTRY_GPIO("cs-gpios", &cs42l43_gpiochip_swnode, 0, GPIO_ACTIVE_LOW),
> +	{ }
> +};

This drops the undefined node, that is important as it lets the
SPI core know that device is using an internal chip select rather
than a GPIO.

> +static const struct software_node cs42l43_spi_swnode = {
> +	.properties = cs42l43_cs_props,
> +};
> +
>  static const struct mfd_cell cs42l43_devs[] = {
> -	{ .name = "cs42l43-pinctrl", },
> -	{ .name = "cs42l43-spi", },
> +	{
> +		.name = "cs42l43-pinctrl",
> +		.swnode = &cs42l43_gpiochip_swnode,
> +	},
> +	{
> +		.name = "cs42l43-spi",
> +		.swnode = &cs42l43_spi_swnode,

I will need to think about this a little more but I suspect this
no longer being conditional on the magic ACPI properties could
cause issues if a system was to use the SPI controller more
traditionally and actually have CS GPIOs in the firmware.
Although maybe that real node would take preference over the
swnode?

Thanks,
Charles