Libpayload: Add keyboard-disble function.

Add a function to disable and clear the keyboard controller.

BUG=chrome-os-partner:20758
TEST=Verified Code flow in normal boot/S3 resume with print statements.
     Verified Keyboard was correctly disabled and flushed by booting
     to recovery mode screen while pressing keys on the integrated
     keyboard.
BRANCH=none

Change-Id: I3e1f011c3436fee5ce10993c6c26a3c8597c6fca
Signed-off-by: Martin Roth <martin.roth@se-eng.com>
Reviewed-on: https://gerrit.chromium.org/gerrit/63627
Reviewed-by: Shawn Nematbakhsh <shawnn@chromium.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: Shawn Nematbakhsh <shawnn@chromium.org>
Commit-Queue: Shawn Nematbakhsh <shawnn@chromium.org>

payloads/libpayload/drivers/keyboard.c

@@ -33,6 +33,7 @@
 
 #define I8042_CMD_READ_MODE  0x20
 #define I8042_CMD_WRITE_MODE 0x60
+#define I8042_CMD_DIS_KB     0xad
 
 #define I8042_MODE_XLATE     0x40
 
@@ -352,3 +353,22 @@ void keyboard_init(void)
 	console_add_input_driver(&cons);
 }
 
+void keyboard_disconnect(void)
+{
+	/* If 0x64 returns 0xff, then we have no keyboard
+	 * controller */
+	if (inb(0x64) == 0xFF)
+		return;
+
+	/* Empty keyboard buffer */
+	while (keyboard_havechar())
+		keyboard_getchar();
+
+	/* Send keyboard disconnect command */
+	outb(I8042_CMD_DIS_KB, 0x64);
+	keyboard_wait_write();
+
+	/* Hand off with empty buffer */
+	while (keyboard_havechar())
+		keyboard_getchar();
+}

payloads/libpayload/include/libpayload.h

@@ -150,6 +150,7 @@ int add_reset_handler(void (*new_handler)(void));
  * @{
  */
 void keyboard_init(void);
+void keyboard_disconnect(void);
 int keyboard_havechar(void);
 unsigned char keyboard_get_scancode(void);
 int keyboard_getchar(void);