| Message ID | 1464779939-24986-2-git-send-email-zhang.chunyan@linaro.org |
|---|---|
| State | New |
| Headers | show |
On Wed, Jun 8, 2016 at 8:13 PM, Alexander Shishkin <alexander.shishkin@linux.intel.com> wrote: > 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. Ok, got it now. I'll revise this change log in the next version. > >>>> +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. Yes, I just looked at stm_console implementation, it is an good example. I may finally got your point. Declaring stm_ftrace as a struct, then Ftrace only needs an instance of stm_ftrace from its own side. That way, ftrace subsystem and stm_ftrace are more independent of each other, and stm_ftrace can be dynamically loaded/unloaded like you suggested. I will revise this patchset. Thanks for your comments, Chunyan > > Regards, > -- > Alex
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>");
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 -- 1.9.1