usb: gadget: functions: add ftrace export over USB

Allow for ftrace data to be exported over a USB Gadget Controller. With this, we have a potentially very fast pipe for transmitting ftrace data to a Host PC for further analysis.

Note that in order to decode the data, one needs access to kernel symbols in order to convert binary data into function names and what not.

Signed-off-by Felipe Balbi <[email protected]>

---
 drivers/usb/gadget/Kconfig            |  15 +
 drivers/usb/gadget/function/Makefile  |   2 +
 drivers/usb/gadget/function/f-trace.c | 401 ++++++++++++++++++++++++++
 3 files changed, 418 insertions(+)
 create mode 100644 drivers/usb/gadget/function/f-trace.c

drivers/usb/gadget/Kconfig +15 -0

index 31cce7805eb2..dfd181e0d717 100644
@@ -191,6 +191,9 @@ config USB_F_MASS_STORAGE
 config USB_F_FS
 	tristate
 
+config USB_F_TRACE
+	tristate
+
 config USB_F_UAC1
 	tristate
 

@@ -368,6 +371,18 @@ config USB_CONFIGFS_F_FS
 	  implemented in kernel space (for instance Ethernet, serial or
 	  mass storage) and other are implemented in user space.
 
+config USB_CONFIGFS_F_TRACE
+	bool "Linux FTrace Export Over USB"
+	depends on USB_CONFIGFS
+	select USB_F_TRACE
+	help
+	  The Linux FTrace Export Over USB lets one export ftrace buffer
+	  over a USB cable to a host computer for further processing.
+
+	  If you want support for that, say Y or M here. Otherwise say N.
+
+	  If unsure, say N.
+
 config USB_CONFIGFS_F_UAC1
 	bool "Audio Class 1.0"
 	depends on USB_CONFIGFS

drivers/usb/gadget/function/Makefile +2 -0

index 5d3a6cf02218..eb851309006c 100644
@@ -50,3 +50,5 @@ usb_f_printer-y			:= f_printer.o
 obj-$(CONFIG_USB_F_PRINTER)	+= usb_f_printer.o
 usb_f_tcm-y			:= f_tcm.o
 obj-$(CONFIG_USB_F_TCM)		+= usb_f_tcm.o
+usb_f_trace-y			:= f-trace.o
+obj-$(CONFIG_USB_F_TRACE)	+= usb_f_trace.o

drivers/usb/gadget/function/f-trace.c new file +52 -0

new file mode 100644
index 000000000000..b5941df128a0
@@ -0,0 +1,401 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * f_trace.c -- USB FTrace Export
+ *
+ * Copyright (C) 2019 Intel Corporation
+ * Author: Felipe Balbi <[email protected]>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License v2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/trace.h>
+#include <linux/usb.h>
+#include <linux/usb/composite.h>
+#include <linux/usb/gadget.h>
+#include <linux/workqueue.h>
+
+struct usb_ftrace {
+	struct trace_export ftrace;
+	struct usb_function function;
+	struct work_struct queue_work;
+	spinlock_t lock;
+
+	struct list_head list;
+	struct list_head pending;
+	struct list_head queued;
+
+	struct usb_ep *in;
+
+	u8 intf_id;
+};
+#define ftrace_to_trace(f)	(container_of((f), struct usb_ftrace, ftrace))
+#define work_to_trace(w)	(container_of((w), struct usb_ftrace, queue_work))
+#define to_trace(f)		(container_of((f), struct usb_ftrace, function))
+
+#define FTRACE_REQUEST_QUEUE_LENGTH	250
+
+static inline struct usb_request *next_request(struct list_head *list)
+{
+	return list_first_entry_or_null(list, struct usb_request, list);
+}
+
+struct usb_ftrace_opts {
+	struct usb_function_instance func_inst;
+};