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

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Message-ID: <CAG2=9p887oYaUhAgg23dO+DZDGYVQ1bef3TZ1jh-xF38=hrHJQ@mail.gmail.com>
Date:   Fri, 21 Oct 2016 20:13:54 +0800
From:   Chunyan Zhang <zhang.chunyan@...aro.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        mingo@...hat.com, Mike Leach <mike.leach@....com>,
        Tor Jeremiassen <tor@...com>, philippe.langlais@...com,
        Nicolas GUION <nicolas.guion@...com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Lyra Zhang <zhang.lyra@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH V7 2/3] stm class: ftrace: Add ftrace-export-over-stm driver

On 19 October 2016 at 00:29, Steven Rostedt <rostedt@...dmis.org> wrote:
> 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

I think we should support other type of tracer in the future, but
you're right it only should depend on FUNCTION_TRACER for now, I will
revise this.

>
>> +     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.

Right, it's not required indeed, will remove it.

Thanks,
Chunyan

>
> -- 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>");
>