spring: Prevent cutting off power on sysjump

If the battery is dead, we must ensure the input current is not cut off
on sysjump. To do so, we record the time of the jump and the I_LIM PWM
duty cycle when jumping. Within 20 seconds from the jump, restrict the
input current to be equal to or higher than that when jumping. This will
ensure the system have at least the same amount of power as when sysjump
happens.

If the user switches to a low power charger within the 20-second
interval, the worst case is that the charger browns out and then recover
after 20 seconds, which should be fine.

BUG=chrome-os-partner:23055
TEST=Unplug battery and do 'sysjump RW' in S0. Without this CL, the AP
shuts down and the EC browns out. With this CL, the AP remains in S0.
BRANCH=Spring

Change-Id: Icf12cd2ec3a59786c01e0b1464a6f094e7c12756
Signed-off-by: Vic Yang <victoryang@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/173073
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
Commit-Queue: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>

1 files changed, 32 insertions, 4 deletions

diff --git a/board/spring/usb_charging.c b/board/spring/usb_charging.c
index 2125dc8ec3..4032a63bee 100644
--- a/board/spring/usb_charging.c
+++ b/board/spring/usb_charging.c
@@ -88,6 +88,9 @@
 #define S5_BOOST_CTRL_LOWER_BOUND 94
 #define S5_BOOST_CTRL_UPPER_BOUND 98
 
+static timestamp_t jump_time;
+static int jump_pwm_duty;
+
 static int current_dev_type = TSU6721_TYPE_NONE;
 static int nominal_pwm_duty;
 static int current_pwm_duty;
@@ -214,7 +217,12 @@ static void board_ilim_use_pwm(void)
 	 */
 	STM32_TIM_PSC(3) = CPU_CLOCK / PWM_FREQUENCY / 100 - 1; /* pre-scaler */
 	STM32_TIM_ARR(3) = 100;			/* auto-reload value */
-	STM32_TIM_CCR1(3) = 100;		/* duty cycle */
+
+	/*
+	 * Note that we don't set STM32_TIM_CCR1 here so as to prevent
+	 * setting a wrong value. The caller of this function must ensure
+	 * STM32_TIM_CCR1 is set correctly before calling this function.
+	 */
 
 	/* CC1 configured as output, PWM mode 1, preload enable */
 	STM32_TIM_CCMR1(3) = (6 << 4) | (1 << 3);
@@ -349,18 +357,38 @@ int board_has_high_power_ac(void)
 
 void board_pwm_duty_cycle(int percent)
 {
-	if (current_ilim_config != ILIM_CONFIG_PWM)
-		board_ilim_config(ILIM_CONFIG_PWM);
 	if (percent < 0)
 		percent = 0;
 	if (percent > 100)
 		percent = 100;
-	STM32_TIM_CCR1(3) = (percent * STM32_TIM_ARR(3)) / 100;
+
+	/*
+	 * If we are in RW, we need to prevent unsetting the PWM duty cycle RO
+	 * set. Otherwise the EC might cut its own power when the battery is
+	 * dead.
+	 *
+	 * If we jumped from RO within the last 20 seconds, only allow higher
+	 * current than that when jumping.
+	 */
+	if (system_get_image_copy() == SYSTEM_IMAGE_RW) {
+		if (get_time().val - jump_time.val < (20 * SECOND) &&
+		    percent > jump_pwm_duty)
+			percent = jump_pwm_duty;
+	}
+
+	STM32_TIM_CCR1(3) = percent;
+	if (current_ilim_config != ILIM_CONFIG_PWM)
+		board_ilim_config(ILIM_CONFIG_PWM);
 	current_pwm_duty = percent;
 }
 
 void board_pwm_init_limit(void)
 {
+	if (system_get_image_copy() == SYSTEM_IMAGE_RW) {
+		jump_time = get_time();
+		jump_pwm_duty = STM32_TIM_CCR1(3);
+	}
+
 	/*
 	 * put a high initial limit to avoid browning out the system
 	 * when we turn on charging, lower power bricks might cut off