poppy: Enable vbus discharge using PD discharge registers

poppy uses an ISL charger, which, unlike bd9995* charger based
systems, cannot provide an interrupt when VBUS falls below/rises
above a certain threshold.

On poppy rev2 onwards, we have a precise VBUS detection pin coming
from BC1.2 detection chip (PI3USB9281C), we a threshold between
3.1-3.7 V (3.5V typical) so we can use that to
enable discharge, according to this logic:
- When VBUS voltage falls below ~3.5V, and we're not sourcing 5V
  to the port, enable discharge.
- When VBUS voltage rises above ~3.5V, disable discharge.
- When we source 5V to the port, disable discharge.

BRANCH=none
BUG=b:37525769
TEST=Charge out to device (Galaxy S8), and verify that VBUS
     drops to 0.8V much faster than without this patch.
TEST=pd 0 swap power: 28ms (vs 496ms)
TEST=pd 1 swap power: 24ms to 0.875v, 202ms to 0.8v (vs 410ms)
TEST=Disconnect cable (port 0): 65ms (vs 721ms)
TEST=Disconnect cable (port 1): 13ms (vs 515ms)

Change-Id: Ibf2dcf5de31514fa0ce0ebd0c6db53d421a586fe
Reviewed-on: https://chromium-review.googlesource.com/481562
Commit-Ready: Nicolas Boichat <drinkcat@chromium.org>
Tested-by: Nicolas Boichat <drinkcat@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>

2 files changed, 27 insertions, 0 deletions

diff --git a/board/poppy/board.c b/board/poppy/board.c
index 85c24610a3..6af2494333 100644
--- a/board/poppy/board.c
+++ b/board/poppy/board.c
@@ -70,11 +70,25 @@ static void tcpc_alert_event(enum gpio_signal signal)
 #endif
 }
 
+/* Set PD discharge whenever VBUS detection is high (i.e. below threshold). */
+static void vbus_discharge_handler(void)
+{
+	if (system_get_board_version() >= 2) {
+		pd_set_vbus_discharge(0,
+				gpio_get_level(GPIO_USB_C0_VBUS_WAKE_L));
+		pd_set_vbus_discharge(1,
+				gpio_get_level(GPIO_USB_C1_VBUS_WAKE_L));
+	}
+}
+DECLARE_DEFERRED(vbus_discharge_handler);
+
 void vbus0_evt(enum gpio_signal signal)
 {
 	/* VBUS present GPIO is inverted */
 	usb_charger_vbus_change(0, !gpio_get_level(signal));
 	task_wake(TASK_ID_PD_C0);
+
+	hook_call_deferred(&vbus_discharge_handler_data, 0);
 }
 
 void vbus1_evt(enum gpio_signal signal)
@@ -82,6 +96,8 @@ void vbus1_evt(enum gpio_signal signal)
 	/* VBUS present GPIO is inverted */
 	usb_charger_vbus_change(1, !gpio_get_level(signal));
 	task_wake(TASK_ID_PD_C1);
+
+	hook_call_deferred(&vbus_discharge_handler_data, 0);
 }
 
 void usb0_evt(enum gpio_signal signal)
diff --git a/board/poppy/usb_pd_policy.c b/board/poppy/usb_pd_policy.c
index 085b86e738..f7d7bd874d 100644
--- a/board/poppy/usb_pd_policy.c
+++ b/board/poppy/usb_pd_policy.c
@@ -118,6 +118,9 @@ int pd_set_power_supply_ready(int port)
 	vbus_en[port] = 1;
 	board_vbus_update_source_current(port);
 
+	if (system_get_board_version() >= 2)
+		pd_set_vbus_discharge(port, 0);
+
 	/* notify host of power info change */
 	pd_send_host_event(PD_EVENT_POWER_CHANGE);
 
@@ -126,10 +129,18 @@ int pd_set_power_supply_ready(int port)
 
 void pd_power_supply_reset(int port)
 {
+	int prev_en;
+
+	prev_en = vbus_en[port];
+
 	/* Disable VBUS */
 	vbus_en[port] = 0;
 	board_vbus_update_source_current(port);
 
+	/* Enable discharge if we were previously sourcing 5V */
+	if (system_get_board_version() >= 2 && prev_en)
+		pd_set_vbus_discharge(port, 1);
+
 	/* Give back the current quota we are no longer using */
 	charge_manager_source_port(port, 0);