Chunyan Zhang <zhang.chun...@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.chun...@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
