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[RFC PATCH 1/4] STM Ftrace: Adding generic buffer interface driver

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  [RFC PATCH 1/4] STM Ftrace: Adding generic buffer interface driver Chunyan Zhang <zhang.chunyan@linaro.org> - 2016-06-01 13:20 +0200
    Re: [RFC PATCH 1/4] STM Ftrace: Adding generic buffer interface driver Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-06-07 12:30 +0200
      Re: [RFC PATCH 1/4] STM Ftrace: Adding generic buffer interface driver Chunyan Zhang <zhang.chunyan@linaro.org> - 2016-06-08 13:10 +0200
        Re: [RFC PATCH 1/4] STM Ftrace: Adding generic buffer interface driver Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2016-06-08 14:20 +0200

#1411098 — [RFC PATCH 1/4] STM Ftrace: Adding generic buffer interface driver

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: Chunyan Zhang <zhang.chunyan@linaro.org>
---
 drivers/hwtracing/stm/Kconfig      |  9 +++++++
 drivers/hwtracing/stm/Makefile     |  2 ++
 drivers/hwtracing/stm/stm_ftrace.c | 54 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 65 insertions(+)
 create mode 100644 drivers/hwtracing/stm/stm_ftrace.c

diff --git a/drivers/hwtracing/stm/Kconfig b/drivers/hwtracing/stm/Kconfig
index 847a39b..a36633a 100644
--- a/drivers/hwtracing/stm/Kconfig
+++ b/drivers/hwtracing/stm/Kconfig
@@ -39,4 +39,13 @@ config STM_SOURCE_HEARTBEAT
 	  If you want to send heartbeat messages over STM devices,
 	  say Y.
 
+config STM_FTRACE
+	tristate "Redirect/copy the output from kernel Ftrace to STM engine"
+	help
+	  This option can be used to redirect or 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..5eef041 100644
--- a/drivers/hwtracing/stm/Makefile
+++ b/drivers/hwtracing/stm/Makefile
@@ -9,3 +9,5 @@ obj-$(CONFIG_STM_SOURCE_HEARTBEAT)	+= stm_heartbeat.o
 
 stm_console-y		:= console.o
 stm_heartbeat-y		:= heartbeat.o
+
+obj-$(CONFIG_STM_FTRACE)	+= stm_ftrace.o
diff --git a/drivers/hwtracing/stm/stm_ftrace.c b/drivers/hwtracing/stm/stm_ftrace.c
new file mode 100644
index 0000000..0b4eb70
--- /dev/null
+++ b/drivers/hwtracing/stm/stm_ftrace.c
@@ -0,0 +1,54 @@
+/*
+ * 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.
+ */
+
+#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_ftrace_data = {
+	.name		= "stm_ftrace",
+	.nr_chans	= 1,
+};
+
+/**
+ * stm_ftrace_write() - write data to STM via 'stm_ftrace' source
+ * @buf:	buffer containing the data packet
+ * @len:	length of the data packet
+ * @chan:	offset above the start channel number allocated to 'stm_ftrace'
+ */
+void notrace stm_ftrace_write(const char *buf, unsigned int len,
+			      unsigned int chan)
+{
+	stm_source_write(&stm_ftrace_data, chan, buf, len);
+}
+EXPORT_SYMBOL_GPL(stm_ftrace_write);
+
+static int __init stm_ftrace_init(void)
+{
+	return stm_source_register_device(NULL, &stm_ftrace_data);
+}
+
+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>");
-- 
1.9.1

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#1415968

Chunyan Zhang <zhang.chunyan@linaro.org> writes:

> 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.

STM core already provides this exact interface to the rest of the
kernel. You need something that ftrace will call into to export its
traces.

>
> Signed-off-by: Chunyan Zhang <zhang.chunyan@linaro.org>
> ---
>  drivers/hwtracing/stm/Kconfig      |  9 +++++++
>  drivers/hwtracing/stm/Makefile     |  2 ++
>  drivers/hwtracing/stm/stm_ftrace.c | 54 ++++++++++++++++++++++++++++++++++++++
>  3 files changed, 65 insertions(+)
>  create mode 100644 drivers/hwtracing/stm/stm_ftrace.c
>
> diff --git a/drivers/hwtracing/stm/Kconfig b/drivers/hwtracing/stm/Kconfig
> index 847a39b..a36633a 100644
> --- a/drivers/hwtracing/stm/Kconfig
> +++ b/drivers/hwtracing/stm/Kconfig
> @@ -39,4 +39,13 @@ config STM_SOURCE_HEARTBEAT
>  	  If you want to send heartbeat messages over STM devices,
>  	  say Y.
>  
> +config STM_FTRACE
> +	tristate "Redirect/copy the output from kernel Ftrace to STM engine"
> +	help
> +	  This option can be used to redirect or copy the output from kernel Ftrace
> +	  to STM engine. Enabling this option will introduce a slight timing effect.

This creates an impression that STM_FTRACE will somehow make events
bypass the normal ftrace ring buffer.

> +
> +	  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..5eef041 100644
> --- a/drivers/hwtracing/stm/Makefile
> +++ b/drivers/hwtracing/stm/Makefile
> @@ -9,3 +9,5 @@ obj-$(CONFIG_STM_SOURCE_HEARTBEAT)	+= stm_heartbeat.o
>  
>  stm_console-y		:= console.o
>  stm_heartbeat-y		:= heartbeat.o
> +
> +obj-$(CONFIG_STM_FTRACE)	+= stm_ftrace.o

We don't have any other source files prefixed with "stm_" in
drivers/hwtracing/stm, because the directory is already "stm".

> diff --git a/drivers/hwtracing/stm/stm_ftrace.c b/drivers/hwtracing/stm/stm_ftrace.c
> new file mode 100644
> index 0000000..0b4eb70
> --- /dev/null
> +++ b/drivers/hwtracing/stm/stm_ftrace.c
> @@ -0,0 +1,54 @@
> +/*
> + * 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.
> + */
> +
> +#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_ftrace_data = {
> +	.name		= "stm_ftrace",
> +	.nr_chans	= 1,

Unless you want to allocate one channel per cpu core, which might or
might not be more efficient, but it would be nice to see at least a
comment about it.

> +};
> +
> +/**
> + * stm_ftrace_write() - write data to STM via 'stm_ftrace' source
> + * @buf:	buffer containing the data packet
> + * @len:	length of the data packet
> + * @chan:	offset above the start channel number allocated to 'stm_ftrace'
> + */
> +void notrace stm_ftrace_write(const char *buf, unsigned int len,
> +			      unsigned int chan)
> +{
> +	stm_source_write(&stm_ftrace_data, chan, buf, len);
> +}
> +EXPORT_SYMBOL_GPL(stm_ftrace_write);

An extra wrapper around stm_source_write().

> +
> +static int __init stm_ftrace_init(void)
> +{
> +	return stm_source_register_device(NULL, &stm_ftrace_data);
> +}
> +
> +static void __exit stm_ftrace_exit(void)
> +{
> +	stm_source_unregister_device(&stm_ftrace_data);
> +}

So basically when ftrace is compiled in, it will pull in stm core
through this.

Regards,
--
Alex

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#1417296

On Tue, Jun 7, 2016 at 6:25 PM, Alexander Shishkin
<alexander.shishkin@linux.intel.com> wrote:
> Chunyan Zhang <zhang.chunyan@linaro.org> writes:
>
>> 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.
>
> STM core already provides this exact interface to the rest of the

Can you point out 'this exact interface' to me?

> kernel. You need something that ftrace will call into to export its
> traces.
>
>>
>> Signed-off-by: Chunyan Zhang <zhang.chunyan@linaro.org>
>> ---
>>  drivers/hwtracing/stm/Kconfig      |  9 +++++++
>>  drivers/hwtracing/stm/Makefile     |  2 ++
>>  drivers/hwtracing/stm/stm_ftrace.c | 54 ++++++++++++++++++++++++++++++++++++++
>>  3 files changed, 65 insertions(+)
>>  create mode 100644 drivers/hwtracing/stm/stm_ftrace.c
>>
>> diff --git a/drivers/hwtracing/stm/Kconfig b/drivers/hwtracing/stm/Kconfig
>> index 847a39b..a36633a 100644
>> --- a/drivers/hwtracing/stm/Kconfig
>> +++ b/drivers/hwtracing/stm/Kconfig
>> @@ -39,4 +39,13 @@ config STM_SOURCE_HEARTBEAT
>>         If you want to send heartbeat messages over STM devices,
>>         say Y.
>>
>> +config STM_FTRACE
>> +     tristate "Redirect/copy the output from kernel Ftrace to STM engine"
>> +     help
>> +       This option can be used to redirect or copy the output from kernel Ftrace
>> +       to STM engine. Enabling this option will introduce a slight timing effect.
>
> This creates an impression that STM_FTRACE will somehow make events
> bypass the normal ftrace ring buffer.

Ok, this name can be adjusted, do you have a better one for me :)

>
>> +
>> +       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..5eef041 100644
>> --- a/drivers/hwtracing/stm/Makefile
>> +++ b/drivers/hwtracing/stm/Makefile
>> @@ -9,3 +9,5 @@ obj-$(CONFIG_STM_SOURCE_HEARTBEAT)    += stm_heartbeat.o
>>
>>  stm_console-y                := console.o
>>  stm_heartbeat-y              := heartbeat.o
>> +
>> +obj-$(CONFIG_STM_FTRACE)     += stm_ftrace.o
>
> We don't have any other source files prefixed with "stm_" in
> drivers/hwtracing/stm, because the directory is already "stm".

Ok, I will remove 'stm_' prefix.

>
>> diff --git a/drivers/hwtracing/stm/stm_ftrace.c b/drivers/hwtracing/stm/stm_ftrace.c
>> new file mode 100644
>> index 0000000..0b4eb70
>> --- /dev/null
>> +++ b/drivers/hwtracing/stm/stm_ftrace.c
>> @@ -0,0 +1,54 @@
>> +/*
>> + * 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.
>> + */
>> +
>> +#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_ftrace_data = {
>> +     .name           = "stm_ftrace",
>> +     .nr_chans       = 1,
>
> Unless you want to allocate one channel per cpu core, which might or
> might not be more efficient, but it would be nice to see at least a
> comment about it.
>
>> +};
>> +
>> +/**
>> + * stm_ftrace_write() - write data to STM via 'stm_ftrace' source
>> + * @buf:     buffer containing the data packet
>> + * @len:     length of the data packet
>> + * @chan:    offset above the start channel number allocated to 'stm_ftrace'
>> + */
>> +void notrace stm_ftrace_write(const char *buf, unsigned int len,
>> +                           unsigned int chan)
>> +{
>> +     stm_source_write(&stm_ftrace_data, chan, buf, len);
>> +}
>> +EXPORT_SYMBOL_GPL(stm_ftrace_write);
>
> An extra wrapper around stm_source_write().

Yes, I think it's not good to expose the stm_source to ftrace_stm_func().

>
>> +
>> +static int __init stm_ftrace_init(void)
>> +{
>> +     return stm_source_register_device(NULL, &stm_ftrace_data);
>> +}
>> +
>> +static void __exit stm_ftrace_exit(void)
>> +{
>> +     stm_source_unregister_device(&stm_ftrace_data);
>> +}
>
> So basically when ftrace is compiled in, it will pull in stm core
> through this.

Sorry I cannot get you here.  Could you please explain you concern further?

Thanks,
Chunyan

>
> Regards,
> --
> Alex

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#1417349

Chunyan Zhang <zhang.chunyan@linaro.org> writes:

> On Tue, Jun 7, 2016 at 6:25 PM, Alexander Shishkin
> <alexander.shishkin@linux.intel.com> wrote:
>> Chunyan Zhang <zhang.chunyan@linaro.org> writes:
>>
>>> 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.
>>
>> STM core already provides this exact interface to the rest of the
>
> Can you point out 'this exact interface' to me?

Well, you're saying that this stm_source exports an interface to send
data to STM for the rest of the kernel. Whereas, stm_source already is
that interface.

>>> +config STM_FTRACE
>>> +     tristate "Redirect/copy the output from kernel Ftrace to STM engine"
>>> +     help
>>> +       This option can be used to redirect or copy the output from kernel Ftrace
>>> +       to STM engine. Enabling this option will introduce a slight timing effect.
>>
>> This creates an impression that STM_FTRACE will somehow make events
>> bypass the normal ftrace ring buffer.
>
> Ok, this name can be adjusted, do you have a better one for me :)

What I mean is: from the description it sounds like there is an option
to bypass ftrace ring buffer, but I don't think that's the case at the
moment. I'm also not sure if it's practical at all to do.

>>> +/**
>>> + * stm_ftrace_write() - write data to STM via 'stm_ftrace' source
>>> + * @buf:     buffer containing the data packet
>>> + * @len:     length of the data packet
>>> + * @chan:    offset above the start channel number allocated to 'stm_ftrace'
>>> + */
>>> +void notrace stm_ftrace_write(const char *buf, unsigned int len,
>>> +                           unsigned int chan)
>>> +{
>>> +     stm_source_write(&stm_ftrace_data, chan, buf, len);
>>> +}
>>> +EXPORT_SYMBOL_GPL(stm_ftrace_write);
>>
>> An extra wrapper around stm_source_write().
>
> Yes, I think it's not good to expose the stm_source to ftrace_stm_func().

I understand, but wrapping it into an intermediary function doesn't
really solve it either.

>> So basically when ftrace is compiled in, it will pull in stm core
>> through this.
>
> Sorry I cannot get you here.  Could you please explain you concern further?

Well, if you plug the stm_source driver into the ftrace core (via a
wrapper or directly), you will end up with a link dependency. In other
words, stm_source and by association stm_core will have to be statically
linked.

Look at the way stm_console is done, for example: it registers with both
stm_source class and the console layer dynamically, so that it can be
dynamically loaded/unloaded.

Regards,
--
Alex

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