TCPMv2: Probe cable identity from Ready states

Cable identity may be probed from the SRC_Ready and SNK_Ready states
when a port is:
- Vconn source
- DFP (for PD 2.0)

This change adds probing to the ready states in these conditions.
Additionally, it down-revs the cable revision when sinking and the port
partner is PD 2.0.

BRANCH=None
BUG=b:148834626
TEST=On kindred, verified:
1. When sourcing:
	a. partner with no e-marker is probed no more than 20
	times between discovery probing and ready
	b. cable which was not probed in discovery is probed in ready
2. When sinking:
	a. no probing when partner does not allow us to Vconn source
	b. probing takes place once chromebook is DFP/Vconn source
	with PD 2.0 partner

Signed-off-by: Diana Z <dzigterman@chromium.org>
Change-Id: I27da70e324d617ad4d30285554a8cd3c0e5db3e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2084013
Reviewed-by: Jett Rink <jettrink@chromium.org>

1 files changed, 50 insertions, 1 deletions

diff --git a/common/usbc/usb_pe_drp_sm.c b/common/usbc/usb_pe_drp_sm.c
index f9647f5715..d1e1b6bc56 100644
--- a/common/usbc/usb_pe_drp_sm.c
+++ b/common/usbc/usb_pe_drp_sm.c
@@ -653,6 +653,33 @@ static void pe_invalidate_explicit_contract(int port)
 	PE_CLR_FLAG(port, PE_FLAGS_EXPLICIT_CONTRACT);
 }
 
+/*
+ * Determine if this port may communicate with the cable plug.
+ *
+ * In both PD 2.0 and 3.0 (2.5.4 SOP'/SOP'' Communication with Cable Plugs):
+ *
+ * When no Contract or an Implicit Contract is in place (e.g. after a Power Role
+ * Swap or Fast Role Swap) only the Source port that is supplying Vconn is
+ * allowed to send packets to a Cable Plug
+ *
+ * When in an explicit contract, PD 3.0 requires that a port be Vconn source to
+ * communicate with the cable.  PD 2.0 requires that a port be DFP to
+ * communicate with the cable plug, with an implication that it must be Vconn
+ * source as well (6.3.11 VCONN_Swap Message).
+ */
+static bool pe_can_send_sop_prime(int port)
+{
+	if (PE_CHK_FLAG(port, PE_FLAGS_EXPLICIT_CONTRACT))
+		if (prl_get_rev(port, TCPC_TX_SOP) == PD_REV20)
+			return tc_is_vconn_src(port) &&
+				pe[port].data_role == PD_ROLE_DFP;
+		else
+			return tc_is_vconn_src(port);
+	else
+		return tc_is_vconn_src(port) &&
+			pe[port].power_role == PD_ROLE_SOURCE;
+}
+
 void pe_report_error(int port, enum pe_error e)
 {
 	/* This should only be called from the PD task */
@@ -1226,7 +1253,8 @@ static void pe_src_discovery_run(int port)
 	 * requests properly.
 	 */
 	if (pe[port].cable.discovery == PD_DISC_NEEDED &&
-	    get_time().val > pe[port].discover_port_identity_timer) {
+	    get_time().val > pe[port].discover_port_identity_timer &&
+	    pe_can_send_sop_prime(port)) {
 		set_state_pe(port, PE_VDM_IDENTITY_REQUEST_CBL);
 		return;
 	}
@@ -1559,6 +1587,13 @@ static void pe_src_ready_run(int port)
 		PE_CLR_FLAG(port, PE_FLAGS_FIRST_MSG);
 		pe[port].wait_and_add_jitter_timer = TIMER_DISABLED;
 
+		if (pe[port].cable.discovery == PD_DISC_NEEDED &&
+		    get_time().val > pe[port].discover_port_identity_timer &&
+		    pe_can_send_sop_prime(port)) {
+			set_state_pe(port, PE_VDM_IDENTITY_REQUEST_CBL);
+			return;
+		}
+
 		/*
 		 * Start Port Discovery when:
 		 *   1) The DiscoverIdentityTimer times out.
@@ -2012,6 +2047,13 @@ static void pe_snk_evaluate_capability_entry(int port)
 	prl_set_rev(port, TCPC_TX_SOP, (PD_HEADER_REV(header) > PD_REV30) ?
 					PD_REV30 : PD_HEADER_REV(header));
 
+	/*
+	 * If port partner runs PD 2.0, cable communication must
+	 * also be PD 2.0
+	 */
+	if (prl_get_rev(port, TCPC_TX_SOP) == PD_REV20)
+		prl_set_rev(port, TCPC_TX_SOP_PRIME, PD_REV20);
+
 	pe[port].src_cap_cnt = num;
 
 	for (i = 0; i < num; i++)
@@ -2282,6 +2324,13 @@ static void pe_snk_ready_run(int port)
 			return;
 		}
 
+		if (pe[port].cable.discovery == PD_DISC_NEEDED &&
+		    get_time().val > pe[port].discover_port_identity_timer &&
+		    pe_can_send_sop_prime(port)) {
+			set_state_pe(port, PE_VDM_IDENTITY_REQUEST_CBL);
+			return;
+		}
+
 		/*
 		 * Start Port Discovery when:
 		 *   1) The PortDiscoverIdentityTimer times out.