servo_v4: Fake CC2 voltage when servo v4 as snk

In servo v4 hardware logic, both CC lines are wired directly
to DUT. When servo v4 as a snk, DUT may source Vconn to CC2
and make the voltage high as vRd-3.0, which makes the PD
state mess up. As the PD state machine doesn't handle this
case. It assumes that CC2 is separated by a Type-C cable,
resulting a voltage lower than the max of vRa.

It fakes the voltage within vRa so the PD state machine
checks the value as expected.

This is an issue only happening on servo v4 as it wires both
CC lines to DUT.

BUG=b:134700685
BRANCH=servo
TEST=Servo v4 as snk, verified the CC2 is sensed vRa, i.e.
the output "CC1:0" (TYPEC_CC_VOLT_OPEN), instead of "CC1:7"
(TYPEC_CC_VOLT_SNK_3_0).

2019-06-18 15:05:47 > cc snk
2019-06-18 15:05:50 cc: on
2019-06-18 15:05:50 dts mode: off
2019-06-18 15:05:50 chg mode: off
2019-06-18 15:05:50 chg allowed: off
2019-06-18 15:05:50 > C1 st2 SNK_DISCONNECTED
2019-06-18 15:05:50 C1 st3 SNK_DISCONNECTED_DEBOUNCE
2019-06-18 15:05:50 C1 st5 SNK_DISCOVERY
2019-06-18 15:05:51 > tcpc 1 state
2019-06-18 15:05:53 Port C1, Dis - CC:2, CC0:6, CC1:0
2019-06-18 15:05:53 Alert: 0x00 Mask: 0x007d
2019-06-18 15:05:53 Power Status: 0x48 Mask: 0x00

TEST=Ran the PD FAFT test firmware_PDConnect passed.

Change-Id: I10f1ffe80768100ee3ed4c374598df7c2f9a8d05
Signed-off-by: Wai-Hong Tam <waihong@google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1666468
Reviewed-by: Aseda Aboagye <aaboagye@chromium.org>
(cherry picked from commit 1f14229fa7e499dfcee07d17add187598ff0a46c)
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1686276

1 files changed, 26 insertions, 7 deletions

diff --git a/board/servo_v4/usb_pd_policy.c b/board/servo_v4/usb_pd_policy.c
index 32a1a046d2..e45a920b1e 100644
--- a/board/servo_v4/usb_pd_policy.c
+++ b/board/servo_v4/usb_pd_policy.c
@@ -99,6 +99,10 @@ static int pd_src_rd_threshold[TYPEC_RP_RESERVED] = {
 /* Saved value for the duration of faking PD disconnect */
 static int fake_pd_disconnect_duration_us;
 
+/* Shadow what would be in TCPC register state. */
+static int rp_value_stored = TYPEC_RP_USB;
+static int cc_pull_stored = TYPEC_CC_RD;
+
 /*
  * Set the USB PD max voltage to value appropriate for the board version.
  * The red/blue versions of servo_v4 have an ESD between VBUS and CC1/CC2
@@ -319,9 +323,28 @@ int pd_adc_read(int port, int cc)
 
 	if (port == 0)
 		mv = adc_read_channel(cc ? ADC_CHG_CC2_PD : ADC_CHG_CC1_PD);
-	else if (!disable_cc)
-		mv = adc_read_channel(cc ? ADC_DUT_CC2_PD : ADC_DUT_CC1_PD);
-	else {
+	else if (!disable_cc) {
+		/*
+		 * In servo v4 hardware logic, both CC lines are wired directly
+		 * to DUT. When servo v4 as a snk, DUT may source Vconn to CC2
+		 * and make the voltage high as vRd-3.0, which makes the PD
+		 * state mess up. As the PD state machine doesn't handle this
+		 * case. It assumes that CC2 is separated by a Type-C cable,
+		 * resulting a voltage lower than the max of vRa.
+		 *
+		 * It fakes the voltage within vRa.
+		 *
+		 * TODO(b/136014621): Servo v4 always applies Rd/Rp to CC1 and
+		 * leaves CC2 open. Need change when it supports switching CC
+		 * polarity.
+		 */
+		if (disable_dts_mode && cc_pull_stored == TYPEC_CC_RD &&
+		    port == DUT && cc == 1)
+			mv = 0;
+		else
+			mv = adc_read_channel(cc ? ADC_DUT_CC2_PD :
+						   ADC_DUT_CC1_PD);
+	} else {
 		/*
 		 * When disable_cc, fake the voltage on CC to 0 to avoid
 		 * triggering some debounce logic.
@@ -407,10 +430,6 @@ static int board_set_rp(int rp)
 	return EC_SUCCESS;
 }
 
-/* Shadow what would be in TCPC register state. */
-static int rp_value_stored = TYPEC_RP_USB;
-static int cc_pull_stored = TYPEC_CC_RD;
-
 int pd_set_rp_rd(int port, int cc_pull, int rp_value)
 {
 	int rv = EC_SUCCESS;