LED failed attempt, GPIO working

kernel_config_fragment

@@ -57,3 +57,38 @@ CONFIG_TRACER_SNAPSHOT=y
 # https://stackoverflow.com/questions/20069620/print-kernels-page-table-entries
 # cat /sys/kernel/debug/kernel_page_tables
 CONFIG_X86_PTDUMP=y
+
+# LEDs.
+#
+#     modprobe led-class
+#     modprobe leds-versatile
+#     ls /sys/class/leds
+#
+# TODO: the LEDs don't appear there. There are some entires under:
+#
+#     /sys/devices/platform/10000000.core-module/10000000.core-module:led@08.0/
+#
+# but they don't have brightness file.
+#
+# https://raspberrypi.stackexchange.com/questions/697/how-do-i-control-the-system-leds-using-my-software
+#
+# Relevant QEMU files:
+#
+# - hw/arm/versatilepb.c
+# - hw/misc/arm_sysctl.c
+#
+# Relevant kernel files:
+#
+# - arch/arm/boot/dts/versatile-pb.dts
+# - drivers/leds/led-class.c
+# - drivers/leds/leds-versatile.c
+#
+CONFIG_LEDS_CLASS=y
+CONFIG_LEDS_VERSATILE=y
+CONFIG_NEW_LEDS=y
+
+# GPIO.
+CONFIG_ARM_AMBA=y
+CONFIG_GPIOLIB=y
+CONFIG_GPIO_SYSFS=y
+CONFIG_GPIO_PL061=y