[PATCH 04/11] usb: tcpm: add lightweight PD negotiation tracing
Peng Fan (OSS)
peng.fan at oss.nxp.com
Wed Jun 17 10:23:03 CEST 2026
From: Peng Fan <peng.fan at nxp.com>
Add a zero-overhead ring buffer trace facility for debugging USB PD
negotiation timing issues. Trace points record timestamp and event
to a RAM buffer without any serial output, avoiding interference
with PD protocol timing constraints.
Trace points cover the critical PD sink negotiation path:
- Source_Capabilities reception
- Request construction and transmission
- TX completion polling
- Accept/PS_RDY reception
- SNK_READY state entry
- Post-ready polling
The trace buffer can be dumped on demand via pd_trace_dump() for
post-mortem analysis of PD negotiation failures.
Signed-off-by: Peng Fan <peng.fan at nxp.com>
---
drivers/usb/tcpm/tcpm-internal.h | 40 ++++++++++++++++++++++++++++++++++++++++
drivers/usb/tcpm/tcpm.c | 17 +++++++++++++++++
2 files changed, 57 insertions(+)
diff --git a/drivers/usb/tcpm/tcpm-internal.h b/drivers/usb/tcpm/tcpm-internal.h
index 56144209002..138b0dc089e 100644
--- a/drivers/usb/tcpm/tcpm-internal.h
+++ b/drivers/usb/tcpm/tcpm-internal.h
@@ -166,6 +166,46 @@ struct tcpm_port {
unsigned long delay_target;
};
+#define PD_TRACE_MAX 32
+
+struct pd_trace_entry {
+ unsigned long ts_us;
+ const char *event;
+ u32 val;
+};
+
+struct pd_trace_buf {
+ struct pd_trace_entry entries[PD_TRACE_MAX];
+ int count;
+};
+
+extern struct pd_trace_buf g_pd_trace;
+
+static inline void pd_trace(const char *event, u32 val)
+{
+ if (g_pd_trace.count < PD_TRACE_MAX) {
+ struct pd_trace_entry *e = &g_pd_trace.entries[g_pd_trace.count++];
+
+ e->ts_us = timer_get_us();
+ e->event = event;
+ e->val = val;
+ }
+}
+
+static inline void pd_trace_dump(void)
+{
+ int i;
+ unsigned long base = g_pd_trace.count > 0 ? g_pd_trace.entries[0].ts_us : 0;
+
+ printf("=== PD TRACE (%d entries) ===\n", g_pd_trace.count);
+ for (i = 0; i < g_pd_trace.count; i++) {
+ struct pd_trace_entry *e = &g_pd_trace.entries[i];
+
+ printf("[+%7luus] %-30s 0x%08x\n",
+ e->ts_us - base, e->event, e->val);
+ }
+}
+
extern const char * const tcpm_states[];
int tcpm_post_probe(struct udevice *dev);
diff --git a/drivers/usb/tcpm/tcpm.c b/drivers/usb/tcpm/tcpm.c
index d6af0fae7c1..1ce46118fea 100644
--- a/drivers/usb/tcpm/tcpm.c
+++ b/drivers/usb/tcpm/tcpm.c
@@ -23,6 +23,8 @@ const char * const tcpm_states[] = {
FOREACH_TCPM_STATE(GENERATE_TCPM_STRING)
};
+struct pd_trace_buf g_pd_trace;
+
const char * const typec_pd_rev_name[] = {
[PD_REV10] = "rev1",
[PD_REV20] = "rev2",
@@ -193,7 +195,9 @@ static int tcpm_pd_transmit(struct udevice *dev,
dev_dbg(dev, "TCPM: PD TX, type: %#x\n", type);
port->tx_complete = false;
+ pd_trace("PD_TX_START", type);
ret = drvops->pd_transmit(dev, type, msg, port->negotiated_rev);
+ pd_trace("PD_TX_DONE", ret);
if (ret < 0)
return ret;
@@ -213,6 +217,7 @@ static int tcpm_pd_transmit(struct udevice *dev,
return ret;
}
+ pd_trace("TX_POLL_DONE", port->tx_status);
switch (port->tx_status) {
case TCPC_TX_SUCCESS:
port->message_id = (port->message_id + 1) & PD_HEADER_ID_MASK;
@@ -626,6 +631,7 @@ static void tcpm_pd_data_request(struct udevice *dev,
switch (type) {
case PD_DATA_SOURCE_CAP:
+ pd_trace("RX_SOURCE_CAP", cnt);
for (i = 0; i < cnt; i++)
port->source_caps[i] = le32_to_cpu(msg->payload[i]);
@@ -668,6 +674,7 @@ static void tcpm_pd_data_request(struct udevice *dev,
* but be prepared to keep waiting for VBUS after it was
* handled.
*/
+ pd_trace("SET_SNK_NEGOTIATE", 0);
tcpm_set_state(dev, SNK_NEGOTIATE_CAPABILITIES, 0);
break;
case PD_DATA_REQUEST:
@@ -736,6 +743,7 @@ static void tcpm_pd_ctrl_request(struct udevice *dev,
case PD_CTRL_GOTO_MIN:
break;
case PD_CTRL_PS_RDY:
+ pd_trace("RX_PS_RDY", port->state);
switch (port->state) {
case SNK_TRANSITION_SINK:
if (port->vbus_present) {
@@ -775,6 +783,7 @@ static void tcpm_pd_ctrl_request(struct udevice *dev,
}
break;
case PD_CTRL_ACCEPT:
+ pd_trace("RX_ACCEPT", port->state);
switch (port->state) {
case SNK_NEGOTIATE_CAPABILITIES:
tcpm_set_state(dev, SNK_TRANSITION_SINK, 0);
@@ -1655,9 +1664,13 @@ static void run_state_machine(struct udevice *dev)
}
break;
case SNK_NEGOTIATE_CAPABILITIES:
+ pd_trace("SNK_NEGOTIATE_ENTER", 0);
port->pd_capable = true;
port->hard_reset_count = 0;
ret = tcpm_pd_send_request(dev);
+ pd_trace("SNK_NEGOTIATE_SENT", ret);
+ pd_trace("REQ_MV", port->req_supply_voltage);
+ pd_trace("REQ_MA", port->req_current_limit);
if (ret < 0) {
/* Let the Source send capabilities again. */
tcpm_set_state(dev, SNK_WAIT_CAPABILITIES, 0);
@@ -1672,8 +1685,10 @@ static void run_state_machine(struct udevice *dev)
PD_T_PS_TRANSITION);
break;
case SNK_READY:
+ pd_trace("SNK_READY", 0);
port->update_sink_caps = false;
tcpm_typec_connect(port);
+
/*
* Here poll_event_cnt is cleared, waiting for self-powered Type-C devices
* to send DR_swap Messge until 1s (TCPM_POLL_EVENT_TIME_OUT * 500us)timeout
@@ -2255,11 +2270,13 @@ static void tcpm_poll_event(struct udevice *dev)
if (port->state == SNK_READY || port->state == SRC_READY) {
int settle;
+ pd_trace("POST_READY_POLL_START", port->state);
for (settle = 0; settle < 1000; settle++) {
drvops->poll_event(dev);
udelay(500);
tcpm_check_and_run_delayed_work(dev);
}
+ pd_trace("POST_READY_POLL_DONE", port->state);
}
if (port->state != SNK_READY && port->state != SRC_READY)
--
2.51.0
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