input-wacom: Conditionally compile LED trigger brightness support

This change is only for input-wacom to ensure that it continues to build
properly on older kernels which may not support trigger brightness.

4.18/wacom_sys.c

@@ -1400,8 +1400,10 @@ static int wacom_led_register_one(struct device *dev, struct wacom *wacom,
 
 	if (!read_only) {
 		led->trigger.name = name;
+#ifdef WACOM_TRIGGER_BRIGHTNESS
 		if (id == wacom->led.groups[group].select)
 			led->trigger.brightness = wacom_leds_brightness_get(led);
+#endif
 		error = devm_led_trigger_register(dev, &led->trigger);
 		if (error) {
 			hid_err(wacom->hdev,

configure.ac

@@ -256,6 +256,22 @@ int test(struct hid_usage *usage) { return usage->resolution_multiplier; }
 	AC_MSG_RESULT([no])
 ])
 
+dnl Check if LED triggers define brightness. This should be in Linux
+dnl 6.10 and later.
+AC_MSG_CHECKING(trigger brightness)
+WACOM_LINUX_TRY_COMPILE([
+#include <linux/leds.h>
+int test(struct led_trigger *trigger) { return trigger->brightness; }
+],[
+],[
+	HAVE_TRIGGER_BRIGHTNESS=yes
+	AC_MSG_RESULT([yes])
+	AC_DEFINE([WACOM_TRIGGER_BRIGHTNESS], [], [kernel defines trigger brightness from v6.10+])
+],[
+	HAVE_TRIGGER_BRIGHTNESS=no
+	AC_MSG_RESULT([no])
+])
+
 
 
 dnl Check which version of the driver we should compile