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* [PATCH v3] usb: typec: tcpm: improve handling of DISCOVER_MODES failures
@ 2026-03-09 15:15 Sebastian Reichel
  2026-03-11 13:22 ` Heikki Krogerus
  0 siblings, 1 reply; 2+ messages in thread
From: Sebastian Reichel @ 2026-03-09 15:15 UTC (permalink / raw)
  To: Badhri Jagan Sridharan, Heikki Krogerus, Greg Kroah-Hartman,
	RD Babiera
  Cc: linux-usb, linux-kernel, kernel, stable, Sebastian Reichel

UGREEN USB-C Multifunction Adapter Model CM512 (AKA "Revodok 107")
exposes two SVIDs: 0xff01 (DP Alt Mode) and 0x1d5c. The DISCOVER_MODES
step succeeds for 0xff01 and gets a NAK for 0x1d5c. Currently this
results in DP Alt Mode not being registered either, since the modes
are only registered once all of them have been discovered. The NAK
results in the processing being stopped and thus no Alt modes being
registered.

Improve the situation by handling the NAK gracefully and continue
processing the other modes.

Before this change, the TCPM log ends like this:

(more log entries before this)
[    5.028287] AMS DISCOVER_SVIDS finished
[    5.028291] cc:=4
[    5.040040] SVID 1: 0xff01
[    5.040054] SVID 2: 0x1d5c
[    5.040082] AMS DISCOVER_MODES start
[    5.040096] PD TX, header: 0x1b6f
[    5.050946] PD TX complete, status: 0
[    5.059609] PD RX, header: 0x264f [1]
[    5.059626] Rx VDM cmd 0xff018043 type 1 cmd 3 len 2
[    5.059640] AMS DISCOVER_MODES finished
[    5.059644] cc:=4
[    5.069994]  Alternate mode 0: SVID 0xff01, VDO 1: 0x000c0045
[    5.070029] AMS DISCOVER_MODES start
[    5.070043] PD TX, header: 0x1d6f
[    5.081139] PD TX complete, status: 0
[    5.087498] PD RX, header: 0x184f [1]
[    5.087515] Rx VDM cmd 0x1d5c8083 type 2 cmd 3 len 1
[    5.087529] AMS DISCOVER_MODES finished
[    5.087534] cc:=4
(no further log entries after this point)

After this patch the TCPM log looks exactly the same, but then
continues like this:

[    5.100222] Skip SVID 0x1d5c (failed to discover mode)
[    5.101699] AMS DFP_TO_UFP_ENTER_MODE start
(log goes on as the system initializes DP AltMode)

Cc: stable@vger.kernel.org
Fixes: 41d9d75344d9 ("usb: typec: tcpm: add discover svids and discover modes support for sop'")
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
---
Changes in v3:
- Link to v2: https://lore.kernel.org/r/20260303-tcpm-discover-modes-nak-fix-v2-1-5a630070025a@collabora.com
- Move svdm_consume_modes() out of tcpm_handle_discover_mode() (Heikki Krogerus)
- Move rlen return pointer argument into proper return code (Heikki Krogerus)
- Drop multiple tcpm_handle_discover_mode() arguments by re-getting them
  in the function  (Heikki Krogerus)
- Restructure if/else branches after these changes to make checkpatch happy
- Did not pick up R-b tag from Badhri Jagan Sridharan due to the amount
  of changes

Changes in v2:
- Link to v1: https://lore.kernel.org/r/20260213-tcpm-discover-modes-nak-fix-v1-0-9bcb5adb4ef6@collabora.com
- Squash patches (Badhri Jagan Sridharan)
- Add Fixes tag (Badhri Jagan Sridharan)
- Move common svdm_consume_modes out of conditional statement (Badhri Jagan Sridharan)
- Add TCPM log to commit message (Badhri Jagan Sridharan)
---
 drivers/usb/typec/tcpm/tcpm.c | 97 +++++++++++++++++++++++++++----------------
 1 file changed, 61 insertions(+), 36 deletions(-)

diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index 1d2f3af034c5..97a35b5590d9 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -1995,6 +1995,55 @@ static bool tcpm_cable_vdm_supported(struct tcpm_port *port)
 	       tcpm_can_communicate_sop_prime(port);
 }
 
+static int tcpm_handle_discover_mode(struct tcpm_port *port, u32 *response,
+				     enum tcpm_transmit_type rx_sop_type,
+				     enum tcpm_transmit_type *response_tx_sop_type)
+{
+	struct typec_port *typec = port->typec_port;
+	struct pd_mode_data *modep;
+
+	if (rx_sop_type == TCPC_TX_SOP) {
+		modep = &port->mode_data;
+		modep->svid_index++;
+
+		if (modep->svid_index < modep->nsvids) {
+			u16 svid = modep->svids[modep->svid_index];
+			*response_tx_sop_type = TCPC_TX_SOP;
+			response[0] = VDO(svid, 1,
+					  typec_get_negotiated_svdm_version(typec),
+					  CMD_DISCOVER_MODES);
+			return 1;
+		}
+
+		if (tcpm_cable_vdm_supported(port)) {
+			*response_tx_sop_type = TCPC_TX_SOP_PRIME;
+			response[0] = VDO(USB_SID_PD, 1,
+					  typec_get_cable_svdm_version(typec),
+					  CMD_DISCOVER_SVID);
+			return 1;
+		}
+
+		tcpm_register_partner_altmodes(port);
+	} else if (rx_sop_type == TCPC_TX_SOP_PRIME) {
+		modep = &port->mode_data_prime;
+		modep->svid_index++;
+
+		if (modep->svid_index < modep->nsvids) {
+			u16 svid = modep->svids[modep->svid_index];
+			*response_tx_sop_type = TCPC_TX_SOP_PRIME;
+			response[0] = VDO(svid, 1,
+					  typec_get_cable_svdm_version(typec),
+					  CMD_DISCOVER_MODES);
+			return 1;
+		}
+
+		tcpm_register_plug_altmodes(port);
+		tcpm_register_partner_altmodes(port);
+	}
+
+	return 0;
+}
+
 static int tcpm_pd_svdm(struct tcpm_port *port, struct typec_altmode *adev,
 			const u32 *p, int cnt, u32 *response,
 			enum adev_actions *adev_action,
@@ -2252,41 +2301,11 @@ static int tcpm_pd_svdm(struct tcpm_port *port, struct typec_altmode *adev,
 			}
 			break;
 		case CMD_DISCOVER_MODES:
-			if (rx_sop_type == TCPC_TX_SOP) {
-				/* 6.4.4.3.3 */
-				svdm_consume_modes(port, p, cnt, rx_sop_type);
-				modep->svid_index++;
-				if (modep->svid_index < modep->nsvids) {
-					u16 svid = modep->svids[modep->svid_index];
-					*response_tx_sop_type = TCPC_TX_SOP;
-					response[0] = VDO(svid, 1, svdm_version,
-							  CMD_DISCOVER_MODES);
-					rlen = 1;
-				} else if (tcpm_cable_vdm_supported(port)) {
-					*response_tx_sop_type = TCPC_TX_SOP_PRIME;
-					response[0] = VDO(USB_SID_PD, 1,
-							  typec_get_cable_svdm_version(typec),
-							  CMD_DISCOVER_SVID);
-					rlen = 1;
-				} else {
-					tcpm_register_partner_altmodes(port);
-				}
-			} else if (rx_sop_type == TCPC_TX_SOP_PRIME) {
-				/* 6.4.4.3.3 */
-				svdm_consume_modes(port, p, cnt, rx_sop_type);
-				modep_prime->svid_index++;
-				if (modep_prime->svid_index < modep_prime->nsvids) {
-					u16 svid = modep_prime->svids[modep_prime->svid_index];
-					*response_tx_sop_type = TCPC_TX_SOP_PRIME;
-					response[0] = VDO(svid, 1,
-							  typec_get_cable_svdm_version(typec),
-							  CMD_DISCOVER_MODES);
-					rlen = 1;
-				} else {
-					tcpm_register_plug_altmodes(port);
-					tcpm_register_partner_altmodes(port);
-				}
-			}
+			/* 6.4.4.3.3 */
+			svdm_consume_modes(port, p, cnt, rx_sop_type);
+			rlen = tcpm_handle_discover_mode(port, response,
+							 rx_sop_type,
+							 response_tx_sop_type);
 			break;
 		case CMD_ENTER_MODE:
 			*response_tx_sop_type = rx_sop_type;
@@ -2329,9 +2348,15 @@ static int tcpm_pd_svdm(struct tcpm_port *port, struct typec_altmode *adev,
 		switch (cmd) {
 		case CMD_DISCOVER_IDENT:
 		case CMD_DISCOVER_SVID:
-		case CMD_DISCOVER_MODES:
 		case VDO_CMD_VENDOR(0) ... VDO_CMD_VENDOR(15):
 			break;
+		case CMD_DISCOVER_MODES:
+			tcpm_log(port, "Skip SVID 0x%04x (failed to discover mode)",
+				 PD_VDO_SVID_SVID0(p[0]));
+			rlen = tcpm_handle_discover_mode(port, response,
+							 rx_sop_type,
+							 response_tx_sop_type);
+			break;
 		case CMD_ENTER_MODE:
 			/* Back to USB Operation */
 			*adev_action = ADEV_NOTIFY_USB_AND_QUEUE_VDM;

---
base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f
change-id: 20260213-tcpm-discover-modes-nak-fix-09070bb529c5

Best regards,
-- 
Sebastian Reichel <sebastian.reichel@collabora.com>


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2026-03-09 15:15 [PATCH v3] usb: typec: tcpm: improve handling of DISCOVER_MODES failures Sebastian Reichel
2026-03-11 13:22 ` Heikki Krogerus

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