in case of USB Gadget functions configure through configfs from
a complicated user space program, when switch function from one to another,
if it failed, it is better to find out what action was done to configfs
from user space program.

this change add some trace events which enable/disable a function,
it including add/remove configuration, bind/unbind UDC,
and some attribute files write operation.

Suggested-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Linyu Yuan <redacted>
---
v2: fix two issue Reported-by: kernel test robot [off-list ref]
v3: do not move private structure to configfs.h
v4: add missing new file configfs_trace.h
v5: lost some change of v2, add it again
v6: fix comments from Greg Kroah-Hartman
v7: three minor changes according to coding rules
v8: change two trace location
v9: fix when config is empty
v10: fix wrong api in v9
v11: split to 3 changes, remove read trace, change trace event print format
v12: allocate trace string array per gadget driver

 drivers/usb/gadget/configfs.c       |  17 ++++
 drivers/usb/gadget/configfs_trace.h | 168 ++++++++++++++++++++++++++++++++++++
 2 files changed, 185 insertions(+)
 create mode 100644 drivers/usb/gadget/configfs_trace.h

diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
index 27aa569..6e7d1b1 100644
--- a/drivers/usb/gadget/configfs.c
+++ b/drivers/usb/gadget/configfs.c

@@ -29,6 +29,7 @@ int check_user_usb_string(const char *name,
 
 #define MAX_NAME_LEN	40
 #define MAX_USB_STRING_LANGS 2
+#define MAX_TRACE_STR_LEN	512
 
 static const struct usb_descriptor_header *otg_desc[2];
 

@@ -51,6 +52,9 @@ struct gadget_info {
 	char qw_sign[OS_STRING_QW_SIGN_LEN];
 	spinlock_t spinlock;
 	bool unbind;
+#ifdef CONFIG_TRACING
+	char trace_string[MAX_TRACE_STR_LEN];
+#endif
 };
 
 static inline struct gadget_info *to_gadget_info(struct config_item *item)

@@ -102,6 +106,10 @@ struct gadget_config_name {
 	struct list_head list;
 };
 
+#define CONFIGFS_TRACE_STRING
+#define CREATE_TRACE_POINTS
+#include "configfs_trace.h"
+
 #define USB_MAX_STRING_WITH_NULL_LEN	(USB_MAX_STRING_LEN+1)
 
 static int usb_string_copy(const char *s, char **s_copy)

@@ -212,6 +220,7 @@ static ssize_t gadget_dev_desc_bcdDevice_store(struct config_item *item,
 
 	mutex_lock(&gi->lock);
 	gi->cdev.desc.bcdDevice = cpu_to_le16(bcdDevice);
+	trace_gadget_dev_desc_bcdDevice_store(gi);
 	mutex_unlock(&gi->lock);
 	return len;
 }

@@ -232,6 +241,7 @@ static ssize_t gadget_dev_desc_bcdUSB_store(struct config_item *item,
 
 	mutex_lock(&gi->lock);
 	gi->cdev.desc.bcdUSB = cpu_to_le16(bcdUSB);
+	trace_gadget_dev_desc_bcdUSB_store(gi);
 	mutex_unlock(&gi->lock);
 	return len;
 }

@@ -254,6 +264,7 @@ static int unregister_gadget(struct gadget_info *gi)
 {
 	int ret;
 
+	trace_unregister_gadget(gi);
 	if (!gi->composite.gadget_driver.udc_name)
 		return -ENODEV;
 

@@ -300,6 +311,7 @@ static ssize_t gadget_dev_desc_UDC_store(struct config_item *item,
 			goto err;
 		}
 	}
+	trace_gadget_dev_desc_UDC_store(gi);
 	mutex_unlock(&gi->lock);
 	return len;
 err:

@@ -342,6 +354,7 @@ static ssize_t gadget_dev_desc_max_speed_store(struct config_item *item,
 
 	gi->composite.gadget_driver.max_speed = gi->composite.max_speed;
 
+	trace_gadget_dev_desc_max_speed_store(gi);
 	mutex_unlock(&gi->lock);
 	return len;
 err:

@@ -465,6 +478,7 @@ static int config_usb_cfg_link(
 	list_add_tail(&f->list, &cfg->func_list);
 	ret = 0;
 out:
+	trace_config_usb_cfg_link(gi);
 	mutex_unlock(&gi->lock);
 	return ret;
 }

@@ -496,6 +510,7 @@ static void config_usb_cfg_unlink(
 		if (f->fi == fi) {
 			list_del(&f->list);
 			usb_put_function(f);
+			trace_config_usb_cfg_unlink(gi);
 			mutex_unlock(&gi->lock);
 			return;
 		}

@@ -533,6 +548,7 @@ static ssize_t gadget_config_desc_MaxPower_store(struct config_item *item,
 		return -ERANGE;
 	mutex_lock(&gi->lock);
 	cfg->c.MaxPower = val;
+	trace_gadget_config_desc_MaxPower_store(gi);
 	mutex_unlock(&gi->lock);
 	return len;
 }

@@ -562,6 +578,7 @@ static ssize_t gadget_config_desc_bmAttributes_store(struct config_item *item,
 		return -EINVAL;
 	mutex_lock(&gi->lock);
 	cfg->c.bmAttributes = val;
+	trace_gadget_config_desc_bmAttributes_store(gi);
 	mutex_unlock(&gi->lock);
 	return len;
 }

diff --git a/drivers/usb/gadget/configfs_trace.h b/drivers/usb/gadget/configfs_trace.h
new file mode 100644
index 0000000..d36c61f
--- /dev/null
+++ b/drivers/usb/gadget/configfs_trace.h

@@ -0,0 +1,168 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2021 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#ifdef CONFIGFS_TRACE_STRING
+#undef CONFIGFS_TRACE_STRING
+
+#ifdef CONFIG_TRACING
+static __maybe_unused char *configfs_trace_string(struct gadget_info *gi)
+{
+	struct usb_configuration *uc;
+	struct config_usb_cfg *cfg;
+	struct usb_function *f;
+	size_t len = sizeof(gi->trace_string) - 1;
+	int n = 0;
+
+	if (list_empty(&gi->cdev.configs)) {
+		strcat(gi->trace_string, "empty");
+		return gi->trace_string;
+	}
+
+	list_for_each_entry(uc, &gi->cdev.configs, list) {
+		cfg = container_of(uc, struct config_usb_cfg, c);
+
+		n += scnprintf(gi->trace_string + n, len - n,
+			"{%d %02x %d ",
+			uc->bConfigurationValue,
+			uc->bmAttributes,
+			uc->MaxPower);
+
+		list_for_each_entry(f, &cfg->func_list, list)
+			n += scnprintf(gi->trace_string + n,
+				len - n, "%s,", f->name);
+
+		list_for_each_entry(f, &cfg->c.functions, list)
+			n += scnprintf(gi->trace_string + n,
+				len - n, "%s,", f->name);
+
+		n += scnprintf(gi->trace_string + n, len - n, "};");
+	}
+
+	return gi->trace_string;