drivers/timer/it8xxx2: fix busy wait timer race condition

Command "waitms 50" on ChromeBook EC console, then it will crash EC.

Because arch_busy_wait() is re-entried by two different tasks,
the second calling will reset the timer and may cause the first
calling to fail to reach the waiting destination
(if the first calling's wait time is longer enough).

Verified by follow test pattern:
west build -p auto -b it8xxx2_evb tests/kernel/timer/timer_api
west build -p auto -b it8xxx2_evb tests/kernel/timer/timer_error_case
west build -p auto -b it8xxx2_evb tests/kernel/timer/timer_monotonic
west build -p auto -b it8xxx2_evb tests/kernel/timer/starve
west build -p auto -b it8xxx2_evb tests/kernel/context

Signed-off-by: Ruibin Chang <[email protected]>

Author: RuibinChang

drivers/timer/ite_it8xxx2_timer.c

@@ -150,23 +150,17 @@ void timer_5ms_one_shot(void)
 #ifdef CONFIG_ARCH_HAS_CUSTOM_BUSY_WAIT
 void arch_busy_wait(uint32_t usec_to_wait)
 {
+	uint32_t start = IT8XXX2_EXT_CNTOX(BUSY_WAIT_H_TIMER);
+
 	if (!usec_to_wait) {
 		return;
 	}
 
 	/* Decrease 1us here to calibrate our access registers latency */
 	usec_to_wait--;
 
-	/*
-	 * We want to set the bit(1) re-start busy wait timer as soon
-	 * as possible, so we directly write 0xb instead of | bit(1).
-	 */
-	IT8XXX2_EXT_CTRLX(BUSY_WAIT_L_TIMER) = IT8XXX2_EXT_ETX_COMB_RST_EN;
-
 	for (;;) {
-		uint32_t curr = IT8XXX2_EXT_CNTOX(BUSY_WAIT_H_TIMER);
-
-		if (curr >= usec_to_wait) {
+		if ((IT8XXX2_EXT_CNTOX(BUSY_WAIT_H_TIMER) - start) >= usec_to_wait) {
 			break;
 		}
 	}