TBT: Enter Thunderbolt mode if the cable response timesout

If the passive superspeed cable doesn't support Intel SVID, then the
Thunderbolt cable speed should be set to Passive Gen 2 cable.
Ref: USB Type-C Cable and Connector Specification, Fig F-1.

This commit, checks if the cable is superspeed before returning the
thunderbolt cable speed and sets the overridable maximum speed
supported by the board to TBT_SS_TBT_GEN3.

BUG=b:172364575
BRANCH=None
TEST=Tested on Voxel, able to enter Thunderbolt mode if the cable fails
to respond to Discover SVID SOP'

Signed-off-by: Ayushee Shah <ayushee.shah@intel.com>
Change-Id: Ib5137670c08cbe17166f5a90241ddbcb77e059f7
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2582988
Reviewed-by: Keith Short <keithshort@chromium.org>

4 files changed, 15 insertions, 22 deletions

diff --git a/common/usb_pd_alt_mode_dfp.c b/common/usb_pd_alt_mode_dfp.c
index b0347067ce..8f2643ff1d 100644
--- a/common/usb_pd_alt_mode_dfp.c
+++ b/common/usb_pd_alt_mode_dfp.c
@@ -757,7 +757,7 @@ void set_tbt_compat_mode_ready(int port)
  * Ref: USB Type-C Cable and Connector Specification
  * Figure F-1 TBT3 Discovery Flow
  */
-bool is_tbt_cable_superspeed(int port)
+static bool is_tbt_cable_superspeed(int port)
 {
 	struct pd_discovery *disc;
 
@@ -791,10 +791,15 @@ bool is_tbt_cable_superspeed(int port)
 
 enum tbt_compat_cable_speed get_tbt_cable_speed(int port)
 {
-	union tbt_mode_resp_cable cable_mode_resp = {
-		.raw_value = pd_get_tbt_mode_vdo(port, TCPC_TX_SOP_PRIME) };
-	enum tbt_compat_cable_speed max_tbt_speed =
-				board_get_max_tbt_speed(port);
+	union tbt_mode_resp_cable cable_mode_resp;
+	enum tbt_compat_cable_speed max_tbt_speed;
+
+	if (!is_tbt_cable_superspeed(port))
+		return TBT_SS_RES_0;
+
+	cable_mode_resp.raw_value =
+		pd_get_tbt_mode_vdo(port, TCPC_TX_SOP_PRIME);
+	max_tbt_speed = board_get_max_tbt_speed(port);
 
 	/*
 	 * Ref: USB Type-C Cable and Connector Specification,
@@ -872,13 +877,9 @@ enum tbt_compat_rounded_support get_tbt_rounded_support(int port)
 	return cable_mode_resp.tbt_rounded;
 }
 
-/* Return the current cable speed received from Cable Discover Mode command */
 __overridable enum tbt_compat_cable_speed board_get_max_tbt_speed(int port)
 {
-	union tbt_mode_resp_cable cable_mode_resp = {
-		.raw_value = pd_get_tbt_mode_vdo(port, TCPC_TX_SOP_PRIME) };
-
-	return cable_mode_resp.tbt_cable_speed;
+	return TBT_SS_TBT_GEN3;
 }
 /*
  * ############################################################################
diff --git a/common/usb_pd_policy.c b/common/usb_pd_policy.c
index 5ad4188e54..b480981a2d 100644
--- a/common/usb_pd_policy.c
+++ b/common/usb_pd_policy.c
@@ -487,7 +487,8 @@ static int process_am_discover_ident_sop_prime(int port, int cnt,
 	 * Disable Thunderbolt-compatible mode if the cable does not support
 	 * superspeed.
 	 */
-	if (is_tbt_compat_enabled(port) && !is_tbt_cable_superspeed(port))
+	if (is_tbt_compat_enabled(port) &&
+	    get_tbt_cable_speed(port) < TBT_SS_U31_GEN1)
 		disable_tbt_compat_mode(port);
 
 	return dfp_discover_svids(payload);
diff --git a/common/usbc/tbt_alt_mode.c b/common/usbc/tbt_alt_mode.c
index 144126baa1..23261adb5e 100644
--- a/common/usbc/tbt_alt_mode.c
+++ b/common/usbc/tbt_alt_mode.c
@@ -405,8 +405,7 @@ static bool tbt_mode_is_supported(int port, int vdo_count)
 	if (!disc->identity.idh.modal_support)
 		return false;
 
-	if (!(is_tbt_cable_superspeed(port) &&
-		get_tbt_cable_speed(port) >= TBT_SS_U31_GEN1))
+	if (get_tbt_cable_speed(port) < TBT_SS_U31_GEN1)
 		return false;
 
 	/*
diff --git a/include/usb_pd.h b/include/usb_pd.h
index 52557778cd..19ae64b45f 100644
--- a/include/usb_pd.h
+++ b/include/usb_pd.h
@@ -2168,14 +2168,6 @@ uint32_t pd_get_tbt_mode_vdo(int port, enum tcpm_transmit_type type);
 void set_tbt_compat_mode_ready(int port);
 
 /**
- * Checks if the attached cable supports superspeed
- *
- * @param port	USB-C port number
- * @return      True if cable is superspeed, false otherwise
- */
-bool is_tbt_cable_superspeed(int port);
-
-/**
  * Returns Thunderbolt-compatible cable speed according to the port if,
  * port supports lesser speed than the cable
  *
@@ -2197,7 +2189,7 @@ int enter_tbt_compat_mode(int port, enum tcpm_transmit_type sop,
 			uint32_t *payload);
 
 /**
- * Return maximum allowed speed for Thunderbolt-compatible mode
+ * Return maximum speed supported by the port to enter into Thunderbolt mode
  *
  * NOTE: Chromebooks require that all USB-C ports support the same features,
  * so the maximum speed returned by this function should be set to the lowest