gpio: mxc: configure dynamic GPIO base for CONFIG_GPIO_SYSFS=n

i.MX GPIO numbering has been deterministic since commit 7e6086d
("gpio/mxc: specify gpio base for device tree probe"), a year after
device tree support was first added back in 2011.

Reverting to dynamically allocated GPIO base now would break most
systems making use of the sysfs API. These systems will be eventually
broken by the removal of the sysfs API, but that would result in GPIO
scripts not working instead of essentially toggling at random according
to probe order, which would happen if we unconditionally set base to -1.

Yet, the warning is annoying and has resulted in many rejected attempts
to remove it over the years[1][2][3].

As the i.MX GPIO driver is device tree only, GPIO_SYSFS is the only
consumer of the deterministic GPIO numbering. Let's therefore restrict the
static base and the warning that comes with it to configurations
with CONFIG_GPIO_SYSFS enabled.

[1]: https://lore.kernel.org/all/[email protected]/
[2]: https://lore.kernel.org/all/[email protected]/
[3]: https://lore.kernel.org/all/[email protected]/

Signed-off-by: Ahmad Fatoum <[email protected]>
Reviewed-by: Linus Walleij <[email protected]>
Link: https://lore.kernel.org/r/20250507-b4-imx-gpio-base-warning-v2-1-d43d09e2c6bf@pengutronix.de
Signed-off-by: Bartosz Golaszewski <[email protected]>

Author: a3f

drivers/gpio/gpio-mxc.c

@@ -490,7 +490,14 @@ static int mxc_gpio_probe(struct platform_device *pdev)
 	port->gc.request = mxc_gpio_request;
 	port->gc.free = mxc_gpio_free;
 	port->gc.to_irq = mxc_gpio_to_irq;
-	port->gc.base = of_alias_get_id(np, "gpio") * 32;
+	/*
+	 * Driver is DT-only, so a fixed base needs only be maintained for legacy
+	 * userspace with sysfs interface.
+	 */
+	if (IS_ENABLED(CONFIG_GPIO_SYSFS))
+		port->gc.base = of_alias_get_id(np, "gpio") * 32;
+	else /* silence boot time warning */
+		port->gc.base = -1;
 
 	err = devm_gpiochip_add_data(&pdev->dev, &port->gc, port);
 	if (err)