dm: button: support remapping phone keys

We don't have audio support in U-Boot, but we do have boot menus. Add an
option to re-map the volume and power buttons to up/down/enter so that
in situations where these are the only available buttons (such as on
mobile phones) it's still possible to navigate menus built in U-Boot or
an external EFI app like GRUB or systemd-boot.

Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>

drivers/button/Kconfig

@@ -9,6 +9,17 @@ config BUTTON
 	  can provide access to board-specific buttons. Use of the device tree
 	  for configuration is encouraged.
 
+config BUTTON_REMAP_PHONE_KEYS
+	bool "Remap phone keys for navigation"
+	depends on BUTTON
+	help
+	  Enable remapping of phone keys to navigation keys. This is useful for
+	  devices with phone keys that are not used in U-Boot. The phone keys
+	  are remapped to the following navigation keys:
+	  - Volume up: Up
+	  - Volume down: Down
+	  - Power: Enter
+
 config BUTTON_ADC
 	bool "Button adc"
 	depends on BUTTON

drivers/button/button-uclass.c

@@ -10,6 +10,7 @@
 #include <button.h>
 #include <dm.h>
 #include <dm/uclass-internal.h>
+#include <dt-bindings/input/linux-event-codes.h>
 
 int button_get_by_label(const char *label, struct udevice **devp)
 {
@@ -37,14 +38,33 @@ enum button_state_t button_get_state(struct udevice *dev)
 	return ops->get_state(dev);
 }
 
+static int button_remap_phone_keys(int code)
+{
+	switch (code) {
+	case KEY_VOLUMEUP:
+		return KEY_UP;
+	case KEY_VOLUMEDOWN:
+		return KEY_DOWN;
+	case KEY_POWER:
+		return KEY_ENTER;
+	default:
+		return code;
+	}
+}
+
 int button_get_code(struct udevice *dev)
 {
 	struct button_ops *ops = button_get_ops(dev);
+	int code;
 
 	if (!ops->get_code)
 		return -ENOSYS;
 
-	return ops->get_code(dev);
+	code = ops->get_code(dev);
+	if (CONFIG_IS_ENABLED(BUTTON_REMAP_PHONE_KEYS))
+		return button_remap_phone_keys(code);
+	else
+		return code;
 }
 
 UCLASS_DRIVER(button) = {