HID: apple: option to swap the 'Option' ("Alt") and 'Command' ("Flag") keys.

Use case: people who use both Apple and PC keyboards regularly, and desire to
keep&use their PC muscle memory.

A particular use case: an Apple compact external keyboard connected to a PC
laptop. (This use case can't be covered well by X.org key remappings etc.)
Signed-off-by: Nanno Langstraat <langstr@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-apple.c

@@ -46,6 +46,12 @@ module_param(iso_layout, uint, 0644);
 MODULE_PARM_DESC(iso_layout, "Enable/Disable hardcoded ISO-layout of the keyboard. "
 		"(0 = disabled, [1] = enabled)");
 
+static unsigned int swap_opt_cmd = 0;
+module_param(swap_opt_cmd, uint, 0644);
+MODULE_PARM_DESC(swap_opt_cmd, "Swap the Option (\"Alt\") and Command (\"Flag\") keys. "
+		"(For people who want to keep Windows PC keyboard muscle memory. "
+		"[0] = as-is, Mac layout. 1 = swapped, Windows layout.)");
+
 struct apple_sc {
 	unsigned long quirks;
 	unsigned int fn_on;
@@ -150,6 +156,14 @@ static const struct apple_key_translation apple_iso_keyboard[] = {
 	{ }
 };
 
+static const struct apple_key_translation swapped_option_cmd_keys[] = {
+	{ KEY_LEFTALT,	KEY_LEFTMETA },
+	{ KEY_LEFTMETA,	KEY_LEFTALT },
+	{ KEY_RIGHTALT,	KEY_RIGHTMETA },
+	{ KEY_RIGHTMETA,KEY_RIGHTALT },
+	{ }
+};
+
 static const struct apple_key_translation *apple_find_translation(
 		const struct apple_key_translation *table, u16 from)
 {
@@ -242,6 +256,14 @@ static int hidinput_apple_event(struct hid_device *hid, struct input_dev *input,
 		}
 	}
 
+	if (swap_opt_cmd) {
+		trans = apple_find_translation(swapped_option_cmd_keys, usage->code);
+		if (trans) {
+			input_event(input, usage->type, trans->to, value);
+			return 1;
+		}
+	}
+
 	return 0;
 }