Re: [RFC PATCH v3 1/4] STM trace event: Adding generic buffer interface driver

[Alexander Shishkin <alexander.shishkin@linux.intel.com>]

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

> From: Mathieu Poirier <mathieu.poirier@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: Mathieu Poirier <mathieu.poirier@linaro.org>
> Signed-off-by: Chunyan Zhang <zhang.chunyan@linaro.org>
> ---
>  drivers/stm/Kconfig           | 11 +++++++++++
>  drivers/stm/Makefile          |  2 ++
>  drivers/stm/stm_trace_event.c | 46 +++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 59 insertions(+)
>  create mode 100644 drivers/stm/stm_trace_event.c
>
> diff --git a/drivers/stm/Kconfig b/drivers/stm/Kconfig
> index 6f2db70..8ead418 100644
> --- a/drivers/stm/Kconfig
> +++ b/drivers/stm/Kconfig
> @@ -25,3 +25,14 @@ config STM_SOURCE_CONSOLE
>  
>  	  If you want to send kernel console messages over STM devices,
>  	  say Y.
> +
> +config STM_TRACE_EVENT
> +	tristate "Redirect/copy the output from kernel trace event to STM engine"
> +	depends on STM
> +	help
> +	  This option can be used to redirect or copy the output from kernel trace
> +	  event to STM engine. Enabling this option will introduce a slight
> +	  timing effect.
> +
> +	  If you want to send kernel trace event messages over STM devices,
> +	  say Y.
> diff --git a/drivers/stm/Makefile b/drivers/stm/Makefile
> index 74baf59..55b152c 100644
> --- a/drivers/stm/Makefile
> +++ b/drivers/stm/Makefile
> @@ -5,3 +5,5 @@ stm_core-y		:= core.o policy.o
>  obj-$(CONFIG_STM_DUMMY)	+= dummy_stm.o
>  
>  obj-$(CONFIG_STM_SOURCE_CONSOLE)	+= console.o
> +
> +obj-$(CONFIG_STM_TRACE_EVENT)	+= stm_trace_event.o
> diff --git a/drivers/stm/stm_trace_event.c b/drivers/stm/stm_trace_event.c
> new file mode 100644
> index 0000000..bc77dae
> --- /dev/null
> +++ b/drivers/stm/stm_trace_event.c
> @@ -0,0 +1,46 @@
> +/*
> + * Simple kernel driver to link kernel trace event and an STM device
> + * Copyright (c) 2015, 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_trace_event_data = {
> +	.name		= "stm_trace_event",
> +	.nr_chans	= 1,

One question is: do we want to cram ftrace data from all cpus into one
channel or use a channel per cpu?

Regards,
--
Alex