[RFC PATCH 1/3] STM trace event: Adding generic buffer interface driver

[RFC PATCH 1/3] STM trace event: Adding generic buffer interface driver

[Chunyan Zhang]

From: Mathieu Poirier <mathieu.poirier@linaro.org>

This patch adds a driver that models itself as an stm_source and
who's sole purpose is to export an interface to the rest of the
kernel.  Once the stm and stm_source have been linked via sysfs,
everything that is passed to the interface will endup in the STM
trace engine.

Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Chunyan Zhang <zhang.chunyan@linaro.org>
---
 drivers/stm/Kconfig           | 11 +++++++++++
 drivers/stm/Makefile          |  2 ++
 drivers/stm/stm_trace_event.c | 46 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 59 insertions(+)
 create mode 100644 drivers/stm/stm_trace_event.c

diff --git a/drivers/stm/Kconfig b/drivers/stm/Kconfig
index 6f2db70..8ead418 100644
--- a/drivers/stm/Kconfig
+++ b/drivers/stm/Kconfig
@@ -25,3 +25,14 @@ config STM_SOURCE_CONSOLE

          If you want to send kernel console messages over STM devices,
          say Y.
+
+config STM_TRACE_EVENT
+       tristate "Redirect/copy the output from kernel trace event to
STM engine"
+       depends on STM
+       help
+         This option can be used to redirect or copy the output from
kernel trace
+         event to STM engine. Enabling this option will introduce a slight
+         timing effect.
+
+         If you want to send kernel trace event messages over STM devices,
+         say Y.
diff --git a/drivers/stm/Makefile b/drivers/stm/Makefile
index 74baf59..55b152c 100644
--- a/drivers/stm/Makefile
+++ b/drivers/stm/Makefile
@@ -5,3 +5,5 @@ stm_core-y              := core.o policy.o
 obj-$(CONFIG_STM_DUMMY)        += dummy_stm.o

 obj-$(CONFIG_STM_SOURCE_CONSOLE)       += console.o
+
+obj-$(CONFIG_STM_TRACE_EVENT)  += stm_trace_event.o
diff --git a/drivers/stm/stm_trace_event.c b/drivers/stm/stm_trace_event.c
new file mode 100644
index 0000000..0d787ce
--- /dev/null
+++ b/drivers/stm/stm_trace_event.c
@@ -0,0 +1,46 @@
+/*
+ * Simple kernel driver to link kernel trace event and an STM device
+ * Copyright (c) 2015, 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.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/console.h>
+#include <linux/stm.h>
+
+static struct stm_source_data stm_trace_event_data = {
+       .name           = "stm_trace_event",
+       .nr_chans       = 1,
+};
+
+void stm_trace_event_write(const char *buf, unsigned len)
+{
+       stm_source_write(&stm_trace_event_data, 0, buf, len);
+}
+
+static int stm_trace_event_init(void)
+{
+       return stm_source_register_device(NULL, &stm_trace_event_data);
+}
+
+static void stm_trace_event_exit(void)
+{
+       stm_source_unregister_device(&stm_trace_event_data);
+}
+
+module_init(stm_trace_event_init);
+module_exit(stm_trace_event_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("stm_trace_event driver");
+MODULE_AUTHOR("Mathieu Poirier <mathieu.poirier@linaro.org>");
--
1.9.1

Re: [RFC PATCH 1/3] STM trace event: Adding generic buffer interface driver

[Paul Bolle]

On Fri, 2015-06-05 at 13:37 +0800, Chunyan Zhang wrote:
> --- a/drivers/stm/Kconfig
> +++ b/drivers/stm/Kconfig

> +config STM_TRACE_EVENT
> +       tristate "Redirect/copy the output from kernel trace event to
> STM engine"
> +       depends on STM
> +       help
> +         This option can be used to redirect or copy the output from
> kernel trace
> +         event to STM engine. Enabling this option will introduce a slight
> +         timing effect.
> +
> +         If you want to send kernel trace event messages over STM devices,
> +         say Y.

It seems your mailer (or some mailserver) mangled this part.

> --- /dev/null
> +++ b/drivers/stm/stm_trace_event.c

> +static int stm_trace_event_init(void)
> +{
> +       return stm_source_register_device(NULL, &stm_trace_event_data);
> +}

Is there are reason not to mark this __init?

> +static void stm_trace_event_exit(void)
> +{
> +       stm_source_unregister_device(&stm_trace_event_data);
> +}

Ditto, but here it's __exit, of course.

> +module_init(stm_trace_event_init);
> +module_exit(stm_trace_event_exit);

(These are not rhetorical questions. I actually wonder whether there a
reasons not to mark module_init() and module_exit() functions with
__init and __exit.)


Paul Bolle