[PATCH v1] usb: typec: tcpm: only discover modes the port supports svids for

[RD Babiera <rdbabiera@google.com>]

DisplayPort Alt Mode CTS test 10.3.1 verifies that the device can
recognize the DP SVID in arbitrary locations within the Discover SVIDs
response message. The test expects that the TCPM sends Discover Modes for
the DisplayPort SVID first, but fails because the TCPM sends
Discover Modes for all SVIDs regardless of whether or not the port
supports them.

After discovering the port partner's SVIDs, skip to the first SVID
supported by the device when preparing the Discover Modes request. If
other modes need to be discovered after the first Discover Modes message
is returned, skip over SVIDs not supported by the device.

Fixes: f0690a25a140 ("staging: typec: USB Type-C Port Manager (tcpm)")
Cc: stable@vger.kernel.org
Signed-off-by: RD Babiera <rdbabiera@google.com>
---
 drivers/usb/typec/tcpm/tcpm.c | 46 +++++++++++++++++++++++++++++++----
 1 file changed, 41 insertions(+), 5 deletions(-)

diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index 6e843c511b85..96636a6f1f7c 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -1543,6 +1543,38 @@ static bool svdm_consume_svids(struct tcpm_port *port, const u32 *p, int cnt)
 	return false;
 }
 
+static bool svdm_port_supports_svid(struct tcpm_port *port, u16 svid)
+{
+	int i;
+
+	for (i = 0; i < ALTMODE_DISCOVERY_MAX; i++) {
+		struct typec_altmode *altmode = port->port_altmode[i];
+
+		if (!altmode)
+			return false;
+		if (altmode->svid == svid)
+			return true;
+	}
+	return false;
+}
+
+/*
+ * This helper will continue to return the next supported SVID that the port
+ * needs to send DISCOVER_MODES to until the pmdata->svid_index is incremented after
+ * svdm_consume_modes() in tcpm_pd_svdm().
+ */
+static int svdm_get_next_supported_svid(struct tcpm_port *port, struct pd_mode_data *pmdata)
+{
+	while (pmdata->svid_index < pmdata->nsvids) {
+		u16 svid = pmdata->svids[pmdata->svid_index];
+
+		if (svdm_port_supports_svid(port, svid))
+			return svid;
+		pmdata->svid_index++;
+	}
+	return 0;
+}
+
 static void svdm_consume_modes(struct tcpm_port *port, const u32 *p, int cnt)
 {
 	struct pd_mode_data *pmdata = &port->mode_data;
@@ -1705,9 +1737,11 @@ static int tcpm_pd_svdm(struct tcpm_port *port, struct typec_altmode *adev,
 			if (svdm_consume_svids(port, p, cnt)) {
 				response[0] = VDO(USB_SID_PD, 1, svdm_version, CMD_DISCOVER_SVID);
 				rlen = 1;
-			} else if (modep->nsvids && supports_modal(port)) {
-				response[0] = VDO(modep->svids[0], 1, svdm_version,
-						  CMD_DISCOVER_MODES);
+			} else if (modep->nsvids && supports_modal(port) &&
+				   svdm_get_next_supported_svid(port, modep)) {
+				u16 svid = svdm_get_next_supported_svid(port, modep);
+
+				response[0] = VDO(svid, 1, svdm_version, CMD_DISCOVER_MODES);
 				rlen = 1;
 			}
 			break;
@@ -1715,8 +1749,10 @@ static int tcpm_pd_svdm(struct tcpm_port *port, struct typec_altmode *adev,
 			/* 6.4.4.3.3 */
 			svdm_consume_modes(port, p, cnt);
 			modep->svid_index++;
-			if (modep->svid_index < modep->nsvids) {
-				u16 svid = modep->svids[modep->svid_index];
+			if (modep->svid_index < modep->nsvids &&
+			    svdm_get_next_supported_svid(port, modep)) {
+				u16 svid = svdm_get_next_supported_svid(port, modep);
+
 				response[0] = VDO(svid, 1, svdm_version, CMD_DISCOVER_MODES);
 				rlen = 1;
 			} else {

base-commit: d0d27ef87e1ca974ed93ed4f7d3c123cbd392ba6
-- 
2.42.0.655.g421f12c284-goog