linux-kernel - [PATCH v2 1/2] usb: dwc3: Add trace event for dwc3_set

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Message-ID: <20250822092411.173519-1-khtsai@google.com>
Date: Fri, 22 Aug 2025 17:23:45 +0800
From: Kuen-Han Tsai <khtsai@...gle.com>
To: Thinh.Nguyen@...opsys.com, gregkh@...uxfoundation.org
Cc: linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Kuen-Han Tsai <khtsai@...gle.com>
Subject: [PATCH v2 1/2] usb: dwc3: Add trace event for dwc3_set_prtcap

Changes to the port capability can be indirectly observed by tracing
register writes to DWC3_GCTL. However, this requires interpreting the
raw value, which is neither intuitive nor precise for debugging.
Monitoring these mode changes is essential for resolving issues related
to USB role switching and enumeration.

Introduce a dedicated trace event to provide a human-readable log when
the port capability is configured.

Signed-off-by: Kuen-Han Tsai <khtsai@...gle.com>
Acked-by: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
---
v1 -> v2: Updated the @mode description and added the Acked-by tag.

 drivers/usb/dwc3/core.c  |  1 +
 drivers/usb/dwc3/debug.h | 18 ++++++++++++++++++
 drivers/usb/dwc3/trace.h | 17 +++++++++++++++++
 3 files changed, 36 insertions(+)

diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
index 8002c23a5a02..370fc524a468 100644
--- a/drivers/usb/dwc3/core.c
+++ b/drivers/usb/dwc3/core.c
@@ -156,6 +156,7 @@ void dwc3_set_prtcap(struct dwc3 *dwc, u32 mode, bool ignore_susphy)
 	dwc3_writel(dwc->regs, DWC3_GCTL, reg);

 	dwc->current_dr_role = mode;
+	trace_dwc3_set_prtcap(mode);
 }

 static void __dwc3_set_mode(struct work_struct *work)
diff --git a/drivers/usb/dwc3/debug.h b/drivers/usb/dwc3/debug.h
index 09d703852a92..6e1cdcdce7cc 100644
--- a/drivers/usb/dwc3/debug.h
+++ b/drivers/usb/dwc3/debug.h
@@ -13,6 +13,24 @@

 #include "core.h"

+/**
+ * dwc3_mode_string - returns mode name
+ * @mode: GCTL.PrtCapDir value
+ */
+static inline const char *dwc3_mode_string(u32 mode)
+{
+	switch (mode) {
+	case DWC3_GCTL_PRTCAP_HOST:
+		return "host";
+	case DWC3_GCTL_PRTCAP_DEVICE:
+		return "device";
+	case DWC3_GCTL_PRTCAP_OTG:
+		return "otg";
+	default:
+		return "UNKNOWN";
+	}
+}
+
 /**
  * dwc3_gadget_ep_cmd_string - returns endpoint command string
  * @cmd: command code
diff --git a/drivers/usb/dwc3/trace.h b/drivers/usb/dwc3/trace.h
index bdeb1aaf65d8..b6ba984bafcd 100644
--- a/drivers/usb/dwc3/trace.h
+++ b/drivers/usb/dwc3/trace.h
@@ -19,6 +19,23 @@
 #include "core.h"
 #include "debug.h"

+DECLARE_EVENT_CLASS(dwc3_log_set_prtcap,
+	TP_PROTO(u32 mode),
+	TP_ARGS(mode),
+	TP_STRUCT__entry(
+		__field(u32, mode)
+	),
+	TP_fast_assign(
+		__entry->mode = mode;
+	),
+	TP_printk("mode %s", dwc3_mode_string(__entry->mode))
+);
+
+DEFINE_EVENT(dwc3_log_set_prtcap, dwc3_set_prtcap,
+	TP_PROTO(u32 mode),
+	TP_ARGS(mode)
+);
+
 DECLARE_EVENT_CLASS(dwc3_log_io,
 	TP_PROTO(void *base, u32 offset, u32 value),
 	TP_ARGS(base, offset, value),
--
2.51.0.261.g7ce5a0a67e-goog