gpio: nomadik: grab optional reset control and deassert it at probe

Fetch a reference to the optional shared reset control and deassert it
if it exists.

Optional because not all platforms that use this driver have a reset
attached to the reset block. Shared because some platforms that use the
reset (at least Mobileye EyeQ5) share the reset across banks.

Do not keep a reference to the reset control as it is not needed
afterwards; the driver does not handle suspend, does not use runtime
PM, does not register a remove callback and does not support unbinding
from sysfs (made explicit with suppress_bind_attrs).

The operation is done in nmk_gpio_populate_chip(). This function is
called by either gpio-nomadik or pinctrl-nomadik, whoever comes first.
This is here for historic reasons and could probably be removed now; it
seems gpio-ranges enforces the ordering to be pinctrl-first. It is not
the topic of the present patch however.

Signed-off-by: Théo Lebrun <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Linus Walleij <[e-mail]>

drivers/gpio/gpio-nomadik.c

···
 {
 	struct nmk_gpio_chip *nmk_chip;
 	struct platform_device *gpio_pdev;
+	struct reset_control *reset;
 	struct device *gpio_dev;
 	struct gpio_chip *chip;
 	struct clk *clk;
 	void __iomem *base;
 	u32 id, ngpio;
+	int ret;
 
 	gpio_dev = bus_find_device_by_of_node(&platform_bus_type, np);
 	if (!gpio_dev) {
···
 	}
 	clk_prepare(clk);
 	nmk_chip->clk = clk;
+
+	reset = devm_reset_control_get_optional_shared(gpio_dev, NULL);
+	if (IS_ERR(reset)) {
+		dev_err(&pdev->dev, "failed getting reset control: %ld\n",
+			PTR_ERR(reset));
+		return ERR_CAST(reset);
+	}
+
+	/*
+	 * Reset might be shared and asserts/deasserts calls are unbalanced. We
+	 * only support sharing this reset with other gpio-nomadik devices that
+	 * use this reset to ensure deassertion at probe.
+	 */
+	ret = reset_control_deassert(reset);
+	if (ret) {
+		dev_err(&pdev->dev, "failed reset deassert: %d\n", ret);
+		return ERR_PTR(ret);
+	}
 
 #ifdef CONFIG_PINCTRL_NOMADIK
 	BUG_ON(nmk_chip->bank >= ARRAY_SIZE(nmk_gpio_chips));
···
 	.driver = {
 		.name = "nomadik-gpio",
 		.of_match_table = nmk_gpio_match,
+		.suppress_bind_attrs = true,
 	},
 	.probe = nmk_gpio_probe,
 };