usb_pd_protocol.c: exiting from try.src to attach.src

The port shall transition to Attached.SRC when the SRC.Rd
state is detected on exactly "one of the CC1 or CC2 pins" for
at least tTryCCDebounce. See TypeC v1.4 spec 4.5.2.2.10.2
Exiting from Try.SRC State.

BRANCH=None
BUG=b:130615676
TEST=1.Ampton with apple type-c adapter
     2.Ellisys USB-PD test

Change-Id: I461c53e2b8d9189f290956964754ae5b1a11a950
Signed-off-by: Ruibin Chang <Ruibin.Chang@ite.com.tw>
Reviewed-on: https://chromium-review.googlesource.com/1564499
Commit-Ready: Diana Z <dzigterman@chromium.org>
Reviewed-by: Diana Z <dzigterman@chromium.org>
Reviewed-by: Daisuke Nojiri <dnojiri@chromium.org>
Reviewed-by: Aseda Aboagye <aaboagye@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1600940
Commit-Queue: Diana Z <dzigterman@chromium.org>
Tested-by: Diana Z <dzigterman@chromium.org>

2 files changed, 42 insertions, 10 deletions

diff --git a/common/usb_pd_protocol.c b/common/usb_pd_protocol.c
index e245ddbd56..7d9ade5e2c 100644
--- a/common/usb_pd_protocol.c
+++ b/common/usb_pd_protocol.c
@@ -621,6 +621,14 @@ static void pd_update_saved_port_flags(int port, uint8_t flag, uint8_t val)
 }
 #endif /* defined(CONFIG_USB_PD_DUAL_ROLE) */
 
+/**
+ * Returns true if the port is currently in the try src state.
+ */
+static inline int is_try_src(int port)
+{
+	return pd[port].flags & PD_FLAGS_TRY_SRC;
+}
+
 static inline void set_state(int port, enum pd_states next_state)
 {
 	enum pd_states last_state = pd[port].task_state;
@@ -2929,17 +2937,32 @@ void pd_task(void *u)
 			 */
 			if (auto_toggle_supported &&
 			    !(pd[port].flags & PD_FLAGS_TCPC_DRP_TOGGLE) &&
-			    !(pd[port].flags & PD_FLAGS_TRY_SRC) &&
+			    !is_try_src(port) &&
 			    cc_is_open(cc1, cc2)) {
 				set_state(port, PD_STATE_DRP_AUTO_TOGGLE);
 				timeout = 2*MSEC;
 				break;
 			}
 #endif
-
-			/* Vnc monitoring */
-			if (cc_is_at_least_one_rd(cc1, cc2) ||
-			    cc_is_audio_acc(cc1, cc2)) {
+			/*
+			 * Transition to DEBOUNCE if we detect appropriate
+			 * signals
+			 *
+			 * (from 4.5.2.2.10.2 Exiting from Try.SRC State)
+			 * If try_src -and-
+			 *    have only one Rd (not both) => DEBOUNCE
+			 *
+			 * (from 4.5.2.2.7.2 Exiting from Unattached.SRC State)
+			 * If not try_src -and-
+			 *    have at least one Rd => DEBOUNCE -or-
+			 *    have audio access => DEBOUNCE
+			 *
+			 * try_src should not exit if both pins are Rd
+			 */
+			if ((is_try_src(port) && cc_is_only_one_rd(cc1, cc2)) ||
+			    (!is_try_src(port) &&
+			     (cc_is_at_least_one_rd(cc1, cc2) ||
+			      cc_is_audio_acc(cc1, cc2)))) {
 #ifdef CONFIG_USBC_BACKWARDS_COMPATIBLE_DFP
 				/* Enable VBUS */
 				if (pd_set_power_supply_ready(port))
@@ -2960,7 +2983,7 @@ void pd_task(void *u)
 			 * (PD_T_TRY_TIMEOUT). Otherwise we should stay
 			 * within Try.SRC (break).
 			 */
-			if (pd[port].flags & PD_FLAGS_TRY_SRC) {
+			if (is_try_src(port)) {
 				if (now.val < pd[port].try_src_marker) {
 					break;
 				} else if (now.val < pd[port].try_timeout) {
@@ -3024,9 +3047,10 @@ void pd_task(void *u)
 
 			/* Set debounce timer */
 			if (new_cc_state != pd[port].cc_state) {
-				pd[port].cc_debounce = get_time().val +
-					(pd[port].flags & PD_FLAGS_TRY_SRC) ?
-					PD_T_DEBOUNCE : PD_T_CC_DEBOUNCE;
+				pd[port].cc_debounce =
+					get_time().val +
+					(is_try_src(port) ? PD_T_DEBOUNCE
+							  : PD_T_CC_DEBOUNCE);
 				pd[port].cc_state = new_cc_state;
 				break;
 			}
@@ -3483,7 +3507,7 @@ void pd_task(void *u)
 			 */
 			if (auto_toggle_supported &&
 			    !(pd[port].flags & PD_FLAGS_TCPC_DRP_TOGGLE) &&
-			    !(pd[port].flags & PD_FLAGS_TRY_SRC) &&
+			    !is_try_src(port) &&
 			    cc_is_open(cc1, cc2)) {
 				set_state(port, PD_STATE_DRP_AUTO_TOGGLE);
 				timeout = 2*MSEC;
diff --git a/include/usb_pd_tcpm.h b/include/usb_pd_tcpm.h
index 0a824cc657..2a9778c3dd 100644
--- a/include/usb_pd_tcpm.h
+++ b/include/usb_pd_tcpm.h
@@ -100,6 +100,14 @@ static inline int cc_is_at_least_one_rd(int cc1, int cc2)
 	return cc1 == TYPEC_CC_VOLT_RD || cc2 == TYPEC_CC_VOLT_RD;
 }
 
+/**
+ * Returns true if the port partner is presenting Rd on only one CC line.
+ */
+static inline int cc_is_only_one_rd(int cc1, int cc2)
+{
+	return cc_is_at_least_one_rd(cc1, cc2) && cc1 != cc2;
+}
+
 struct tcpm_drv {
 	/**
 	 * Initialize TCPM driver and wait for TCPC readiness.