This patch adds a driver that models itself as an stm_source called
stm_ftrace. Once the stm device and stm_ftrace have been linked via
sysfs, the driver registers itself as a trace_export and everything
passed to the interface from Ftrace subsystem will end up in the STM
trace engine.

Signed-off-by: Chunyan Zhang <zhang.chun...@linaro.org>
---
 drivers/hwtracing/stm/Kconfig  | 11 ++++++
 drivers/hwtracing/stm/Makefile |  2 +
 drivers/hwtracing/stm/ftrace.c | 88 ++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 101 insertions(+)
 create mode 100644 drivers/hwtracing/stm/ftrace.c

diff --git a/drivers/hwtracing/stm/Kconfig b/drivers/hwtracing/stm/Kconfig
index 847a39b..b34ea96 100644
--- a/drivers/hwtracing/stm/Kconfig
+++ b/drivers/hwtracing/stm/Kconfig
@@ -39,4 +39,15 @@ config STM_SOURCE_HEARTBEAT
          If you want to send heartbeat messages over STM devices,
          say Y.
 
+config STM_SOURCE_FTRACE
+       tristate "Copy the output from kernel Ftrace to STM engine"
+       depends on TRACING
+       help
+         This option can be used to copy the output from kernel Ftrace
+         to STM engine. Enabling this option will introduce a slight
+         timing effect.
+
+         If you want to send kernel Ftrace messages over STM devices,
+         say Y.
+
 endif
diff --git a/drivers/hwtracing/stm/Makefile b/drivers/hwtracing/stm/Makefile
index a9ce3d4..3abd84c 100644
--- a/drivers/hwtracing/stm/Makefile
+++ b/drivers/hwtracing/stm/Makefile
@@ -6,6 +6,8 @@ obj-$(CONFIG_STM_DUMMY) += dummy_stm.o
 
 obj-$(CONFIG_STM_SOURCE_CONSOLE)       += stm_console.o
 obj-$(CONFIG_STM_SOURCE_HEARTBEAT)     += stm_heartbeat.o
+obj-$(CONFIG_STM_SOURCE_FTRACE)                += stm_ftrace.o
 
 stm_console-y          := console.o
 stm_heartbeat-y                := heartbeat.o
+stm_ftrace-y           := ftrace.o
diff --git a/drivers/hwtracing/stm/ftrace.c b/drivers/hwtracing/stm/ftrace.c
new file mode 100644
index 0000000..1a114c8f
--- /dev/null
+++ b/drivers/hwtracing/stm/ftrace.c
@@ -0,0 +1,88 @@
+/*
+ * Simple kernel driver to link kernel Ftrace and an STM device
+ * Copyright (c) 2016, Linaro Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * STM Ftrace will be registered as a trace_export.
+ */
+
+#include <linux/module.h>
+#include <linux/stm.h>
+#include <linux/trace.h>
+
+#define STM_FTRACE_NR_CHANNELS 1
+#define STM_FTRACE_CHAN 0
+
+static int stm_ftrace_link(struct stm_source_data *data);
+static void stm_ftrace_unlink(struct stm_source_data *data);
+
+static struct stm_ftrace {
+       struct stm_source_data  data;
+       struct trace_export     ftrace;
+} stm_ftrace = {
+       .data   = {
+               .name           = "ftrace",
+               .nr_chans       = STM_FTRACE_NR_CHANNELS,
+               .link           = stm_ftrace_link,
+               .unlink         = stm_ftrace_unlink,
+       },
+};
+
+/**
+ * stm_ftrace_write() - write data to STM via 'stm_ftrace' source
+ * @buf:       buffer containing the data packet
+ * @len:       length of the data packet
+ */
+static void notrace
+stm_ftrace_write(const char *buf, unsigned int len)
+{
+       stm_source_write(&stm_ftrace.data, STM_FTRACE_CHAN, buf, len);
+}
+
+static int stm_ftrace_link(struct stm_source_data *data)
+{
+       struct stm_ftrace *sf = container_of(data, struct stm_ftrace, data);
+
+       sf->ftrace.write = stm_ftrace_write;
+       sf->ftrace.next = NULL;
+
+       return register_ftrace_export(&sf->ftrace);
+}
+
+static void stm_ftrace_unlink(struct stm_source_data *data)
+{
+       struct stm_ftrace *sf = container_of(data, struct stm_ftrace, data);
+
+       unregister_ftrace_export(&sf->ftrace);
+}
+
+static int __init stm_ftrace_init(void)
+{
+       int ret;
+
+       ret = stm_source_register_device(NULL, &stm_ftrace.data);
+       if (ret)
+               pr_err("Failed to register stm_source - ftrace.\n");
+
+       return ret;
+}
+
+static void __exit stm_ftrace_exit(void)
+{
+       stm_source_unregister_device(&stm_ftrace.data);
+}
+
+module_init(stm_ftrace_init);
+module_exit(stm_ftrace_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("stm_ftrace driver");
+MODULE_AUTHOR("Chunyan Zhang <zhang.chun...@linaro.org>");
-- 
2.7.4

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