linux-kernel - Re: [PATCH V7 2/3] stm class: ftrace: Add ftrace-export-over-stm driver

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Message-ID: <20161018122928.0c9449a4@gandalf.local.home>
Date:   Tue, 18 Oct 2016 12:29:28 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Chunyan Zhang <zhang.chunyan@...aro.org>
Cc:     mathieu.poirier@...aro.org, alexander.shishkin@...ux.intel.com,
        mingo@...hat.com, mike.leach@....com, tor@...com,
        philippe.langlais@...com, nicolas.guion@...com,
        felipe.balbi@...ux.intel.com, zhang.lyra@...il.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH V7 2/3] stm class: ftrace: Add ftrace-export-over-stm
 driver

On Tue, 18 Oct 2016 16:08:59 +0800
Chunyan Zhang <zhang.chunyan@...aro.org> wrote:

> 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.chunyan@...aro.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

I think it should depend 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 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;

Why setting this to NULL? register_ftrace_export() should not require
nor depend on that.

-- Steve

> +
> +	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@...aro.org>");