stm class: ftrace: Add ftrace-export-over-stm driver

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.

Link: http://lkml.kernel.org/r/1479715043-6534-3-git-send-email-zhang.chunyan@linaro.org

Signed-off-by: Chunyan Zhang <zhang.chunyan@linaro.org>
Acked-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

3 files changed, 100 insertions, 0 deletions

diff --git a/drivers/hwtracing/stm/Kconfig b/drivers/hwtracing/stm/Kconfig
index 847a39b35307..723e2d90083d 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 FUNCTION_TRACER
+        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 a9ce3d487e57..3abd84ce13d4 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 000000000000..bd126a7c6da2
--- /dev/null
+++ b/drivers/hwtracing/stm/ftrace.c
@@ -0,0 +1,87 @@
+/*
+ * 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 void *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;
+
+        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.chunyan@linaro.org>");