[RFC PATCH 0/1] reset: gpio: Add support for GPIO providers with #gpio-cells=3

[bigunclemax@gmail.com]

From: Maksim Kiselev <bigunclemax@gmail.com>

Hello everyone,

A little background.
I have a BigTreeTech CB1 board based on the Allwinner H616.
I decided to try upstream Linux v7.0 and ran into the following issue:

[    0.453297] pwrseq_simple wifi-pwrseq: error -ENOENT: reset control not ready
[    0.460472] pwrseq_simple wifi-pwrseq: probe with driver pwrseq_simple failed with error -2

This error prevents the WiFi chip from coming up.

I started investigating and traced it down to the function
__reset_add_reset_gpio_device() in drivers/reset/core.c:

/*
 * @args:	phandle to the GPIO provider with all the args like GPIO number
 */
static int __reset_add_reset_gpio_device(const struct of_phandle_args *args)
{
	struct property_entry properties[3] = { };
	unsigned int offset, of_flags, lflags;
	struct reset_gpio_lookup *rgpio_dev;
	struct device *parent;
	int id, ret, prop = 0;

	/*
	 * Currently only #gpio-cells=2 is supported with the meaning of:
	 * args[0]: GPIO number
	 * args[1]: GPIO flags
	 * TODO: Handle other cases.
	 */
	if (args->args_count != 2)
		return -ENOENT;

As you can see, a GPIO from controller where #gpio-cells != 2 will cause
an error.

Unfortunately, the Allwinner pinctrl is one such GPIO controller.
It uses three arguments to describe a GPIO line: bank, number, and flags.

Here’s the DT fragment that describes wifi_pwrseq in
arch/arm64/boot/dts/allwinner/sun50i-h616-bigtreetech-cb1.dtsi file:

wifi_pwrseq: wifi-pwrseq {
	compatible = "mmc-pwrseq-simple";
	clocks = <&rtc 1>;
	clock-names = "ext_clock";
	reset-gpios = <&pio 6 18 GPIO_ACTIVE_LOW>; /* PG18 */
	post-power-on-delay-ms = <200>;
};

Potentially this problem could also be observed on other GPIO controllers:
spacemit,k1-gpio, microchip,sparx5-sgpio, and many allwinner,___-pinctrl
variants.

I attempted to make a patch for reset/core.c (not pretty in my opinion)
that adds support for three-args GPIO phandles.
But it seems I’ve fallen down a rabbit hole, because next I hit the fact
that gpiolib-swnode expects GPIOs to be described with exactly
two arguments (swnode_gpio_get_reference()).

I also did a git bisect to find when wifi_pwrseq broke for
the BigTreeTech CB1. It turned out to be commit
73bf4b7381f7 ("mmc: pwrseq_simple: add support for one reset control")
in v6.13-rc1.

So, in theory, a patch to pwrseq_simple.c could be made to fix my issue,
but that wouldn’t solve the underlying reset-gpio problem.

I don’t know how to proceed from here and I’m asking for advice.

Best regards
Maksim

Maksim Kiselev (1):
  reset: add support the GPIO provider with #gpio-cells=3

 drivers/reset/core.c | 33 +++++++++++++++++++++++----------
 1 file changed, 23 insertions(+), 10 deletions(-)

-- 
2.51.0