keyboard: Fix kbpress after recent keyboard change

After commit 98ab7484d331 ("keyboard: prevent races enabling/disabling
kb scanning") kbpress was totally broken, which wasn't so good for
FAFT.  Fix it by making sure we go into polling mode for simulated
keyboard presses.

BUG=chrome-os-partner:48849
TEST=kbpress works

Change-Id: Icd663c2ee7a184e6af4438368595087b35724a4f
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/319586
Reviewed-by: Randall Spangler <rspangler@chromium.org>

common/keyboard_scan.c

@@ -101,6 +101,9 @@ static volatile uint32_t __bss_slow disable_scanning_mask;
 /* Constantly incrementing counter of the number of times we polled */
 static volatile int kbd_polls;
 
+/* If true, we'll force a keyboard poll */
+static volatile int force_poll;
+
 static int keyboard_scan_is_enabled(void)
 {
 	/* NOTE: this is just an instantaneous glimpse of the variable. */
@@ -184,6 +187,9 @@ static void simulate_key(int row, int col, int pressed)
 
 	print_state(simulated_key, "simulated ");
 
+	/* Force a poll even though no keys are pressed */
+	force_poll = 1;
+
 	/* Wake the task to handle changes in simulated keys */
 	task_wake(TASK_ID_KEYSCAN);
 
@@ -664,12 +670,16 @@ void keyboard_scan_task(void)
 			 * user pressing a key and enable_interrupt()
 			 * starting to pay attention to edges.
 			 */
-			if (!local_disable_scanning && keyboard_raw_read_rows())
+			if (!local_disable_scanning &&
+			    (keyboard_raw_read_rows() || force_poll))
 				break;
 			else
 				task_wait_event(-1);
 		}
 
+		/* We're about to poll, so any existing forces are fulfilled */
+		force_poll = 0;
+
 		/* Enter polling mode */
 		CPRINTS("KB poll");
 		keyboard_raw_enable_interrupt(0);