TCPMv2: Debounce Vbus loss when FRS is enabled

A hub may send a Fast Role Swap signal when Vbus is less than vSafe5V,
so allow a 5ms debounce after Vbus loss for the signal to come in before
we declare the connection detached.

BRANCH=None
BUG=b:180453483
TEST=on voxel, confirm FRS behaves normally

Signed-off-by: Diana Z <dzigterman@chromium.org>
Change-Id: If56106660c0a2bf82e28b91129bc9dd367ebc8fe
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2718838
Tested-by: Eric Herrmann <eherrmann@chromium.org>
Reviewed-by: Eric Herrmann <eherrmann@chromium.org>
Reviewed-by: Denis Brockus <dbrockus@chromium.org>

2 files changed, 50 insertions, 6 deletions

diff --git a/common/usbc/usb_tc_drp_acc_trysrc_sm.c b/common/usbc/usb_tc_drp_acc_trysrc_sm.c
index 58fc085a61..50211feacf 100644
--- a/common/usbc/usb_tc_drp_acc_trysrc_sm.c
+++ b/common/usbc/usb_tc_drp_acc_trysrc_sm.c
@@ -2427,6 +2427,46 @@ static void tc_attached_snk_entry(const int port)
 		tcpm_debug_accessory(port, 1);
 }
 
+/*
+ * Check whether Vbus has been removed on this port, accounting for some Vbus
+ * debounce if FRS is enabled.
+ *
+ * Returns true if a new state was set and the calling run should exit.
+ */
+static bool tc_snk_check_vbus_removed(const int port)
+{
+	if (IS_ENABLED(CONFIG_USB_PD_FRS)) {
+		/*
+		 * Debounce Vbus presence when FRS is enabled. Note that we may
+		 * lose Vbus before the FRS signal comes in to let us know
+		 * we're PR swapping, but we must still transition to unattached
+		 * within tSinkDisconnect.
+		 *
+		 * We may safely re-use the Vbus debounce timer here
+		 * since a PR swap would no longer be in progress when Vbus
+		 * removal is checked.
+		 */
+		if (pd_check_vbus_level(port, VBUS_REMOVED)) {
+			if (pd_timer_is_disabled(port,
+						 TC_TIMER_VBUS_DEBOUNCE)) {
+				pd_timer_enable(port, TC_TIMER_VBUS_DEBOUNCE,
+						PD_T_FRS_VBUS_DEBOUNCE);
+			} else if (pd_timer_is_expired(port,
+						TC_TIMER_VBUS_DEBOUNCE)) {
+				set_state_tc(port, TC_UNATTACHED_SNK);
+				return true;
+			}
+		} else {
+			pd_timer_disable(port, TC_TIMER_VBUS_DEBOUNCE);
+		}
+	} else if (pd_check_vbus_level(port, VBUS_REMOVED)) {
+		set_state_tc(port, TC_UNATTACHED_SNK);
+		return true;
+	}
+
+	return false;
+}
+
 static void tc_attached_snk_run(const int port)
 {
 #ifdef CONFIG_USB_PE_SM
@@ -2465,6 +2505,7 @@ static void tc_attached_snk_run(const int port)
 	    pd_timer_is_expired(port, TC_TIMER_VBUS_DEBOUNCE)) {
 		/* PR Swap is no longer in progress */
 		TC_CLR_FLAG(port, TC_FLAGS_PR_SWAP_IN_PROGRESS);
+		pd_timer_disable(port, TC_TIMER_VBUS_DEBOUNCE);
 
 		/*
 		 * AutoDischargeDisconnect was turned off when we
@@ -2485,10 +2526,8 @@ static void tc_attached_snk_run(const int port)
 		/*
 		 * Detach detection
 		 */
-		if (pd_check_vbus_level(port, VBUS_REMOVED)) {
-			set_state_tc(port, TC_UNATTACHED_SNK);
+		if (tc_snk_check_vbus_removed(port))
 			return;
-		}
 
 		if (!pe_is_explicit_contract(port))
 			sink_power_sub_states(port);
@@ -2577,10 +2616,8 @@ static void tc_attached_snk_run(const int port)
 #else /* CONFIG_USB_PE_SM */
 
 	/* Detach detection */
-	if (pd_check_vbus_level(port, VBUS_REMOVED)) {
-		set_state_tc(port, TC_UNATTACHED_SNK);
+	if (tc_snk_check_vbus_removed(port))
 		return;
-	}
 
 	/* Run Sink Power Sub-State */
 	sink_power_sub_states(port);
diff --git a/include/usb_pd.h b/include/usb_pd.h
index 81dbc3220a..ed15149441 100644
--- a/include/usb_pd.h
+++ b/include/usb_pd.h
@@ -246,6 +246,13 @@ enum pd_rx_errors {
 #define PD_T_SYSJUMP              (1000*MSEC) /* 1s */
 #define PD_T_PR_SWAP_WAIT          (100*MSEC) /* tPRSwapWait 100ms */
 
+/*
+ * Non-spec timer to prevent going Unattached if Vbus drops before a partner FRS
+ * signal comes through.  This timer should be shorter than tSinkDisconnect
+ * (40ms) to ensure we still transition out of Attached.SNK in time.
+ */
+#define PD_T_FRS_VBUS_DEBOUNCE	     (5*MSEC)
+
 /* number of edges and time window to detect CC line is not idle */
 #define PD_RX_TRANSITION_COUNT  3
 #define PD_RX_TRANSITION_WINDOW 20 /* between 12us and 20us */