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i2c: Add message transfer tracepoints for I2C
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Add tracepoints into the I2C message transfer function to retrieve the message
sent or received.  The following config options must be turned on to make use
of the facility:

	CONFIG_FTRACE
	CONFIG_ENABLE_DEFAULT_TRACERS

The I2C tracepoint can be enabled thusly:

	echo 1 >/sys/kernel/debug/tracing/events/i2c/enable

and will dump messages that can be viewed in /sys/kernel/debug/tracing/trace
that look like:

	... i2c_write: i2c-5 #0 a=044 f=0000 l=2 [02-14]
	... i2c_read: i2c-5 #1 a=044 f=0001 l=4
	... i2c_reply: i2c-5 #1 a=044 f=0001 l=4 [33-00-00-00]
	... i2c_result: i2c-5 n=2 ret=2

formatted as:

	i2c-<adapter-nr>
	#<message-array-index>
	a=<addr>
	f=<flags>
	l=<datalen>
	n=<message-array-size>
	ret=<result>
	[<data>]

The operation is done between the i2c_write/i2c_read lines and the i2c_reply
and i2c_result lines so that if the hardware hangs, the trace buffer can be
consulted to determine the problematic operation.

The adapters to be traced can be selected by something like:

	echo adapter_nr==1 >/sys/kernel/debug/tracing/events/i2c/filter

These changes are based on code from Steven Rostedt.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
[wsa: adapted path for 'enable' in the commit msg]
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
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@dhowells
dhowells authored and Wolfram Sang committed Mar 13, 2014
1 parent 392debf commit d9a83d6
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37 changes: 37 additions & 0 deletions drivers/i2c/i2c-core.c
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Original file line number Diff line number Diff line change
Expand Up @@ -48,10 +48,13 @@
#include <linux/rwsem.h>
#include <linux/pm_runtime.h>
#include <linux/acpi.h>
#include <linux/jump_label.h>
#include <asm/uaccess.h>

#include "i2c-core.h"

#define CREATE_TRACE_POINTS
#include <trace/events/i2c.h>

/* core_lock protects i2c_adapter_idr, and guarantees
that device detection, deletion of detected devices, and attach_adapter
Expand All @@ -62,6 +65,18 @@ static DEFINE_IDR(i2c_adapter_idr);
static struct device_type i2c_client_type;
static int i2c_detect(struct i2c_adapter *adapter, struct i2c_driver *driver);

static struct static_key i2c_trace_msg = STATIC_KEY_INIT_FALSE;

void i2c_transfer_trace_reg(void)
{
static_key_slow_inc(&i2c_trace_msg);
}

void i2c_transfer_trace_unreg(void)
{
static_key_slow_dec(&i2c_trace_msg);
}

/* ------------------------------------------------------------------------- */

static const struct i2c_device_id *i2c_match_id(const struct i2c_device_id *id,
Expand Down Expand Up @@ -1686,6 +1701,7 @@ static void __exit i2c_exit(void)
class_compat_unregister(i2c_adapter_compat_class);
#endif
bus_unregister(&i2c_bus_type);
tracepoint_synchronize_unregister();
}

/* We must initialize early, because some subsystems register i2c drivers
Expand Down Expand Up @@ -1716,6 +1732,19 @@ int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
unsigned long orig_jiffies;
int ret, try;

/* i2c_trace_msg gets enabled when tracepoint i2c_transfer gets
* enabled. This is an efficient way of keeping the for-loop from
* being executed when not needed.
*/
if (static_key_false(&i2c_trace_msg)) {
int i;
for (i = 0; i < num; i++)
if (msgs[i].flags & I2C_M_RD)
trace_i2c_read(adap, &msgs[i], i);
else
trace_i2c_write(adap, &msgs[i], i);
}

/* Retry automatically on arbitration loss */
orig_jiffies = jiffies;
for (ret = 0, try = 0; try <= adap->retries; try++) {
Expand All @@ -1726,6 +1755,14 @@ int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
break;
}

if (static_key_false(&i2c_trace_msg)) {
int i;
for (i = 0; i < ret; i++)
if (msgs[i].flags & I2C_M_RD)
trace_i2c_reply(adap, &msgs[i], i);
trace_i2c_result(adap, i, ret);
}

return ret;
}
EXPORT_SYMBOL(__i2c_transfer);
Expand Down
150 changes: 150 additions & 0 deletions include/trace/events/i2c.h
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Original file line number Diff line number Diff line change
@@ -0,0 +1,150 @@
/* I2C message transfer tracepoints
*
* Copyright (C) 2013 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/
#undef TRACE_SYSTEM
#define TRACE_SYSTEM i2c

#if !defined(_TRACE_I2C_H) || defined(TRACE_HEADER_MULTI_READ)
#define _TRACE_I2C_H

#include <linux/i2c.h>
#include <linux/tracepoint.h>

/*
* drivers/i2c/i2c-core.c
*/
extern void i2c_transfer_trace_reg(void);
extern void i2c_transfer_trace_unreg(void);

/*
* __i2c_transfer() write request
*/
TRACE_EVENT_FN(i2c_write,
TP_PROTO(const struct i2c_adapter *adap, const struct i2c_msg *msg,
int num),
TP_ARGS(adap, msg, num),
TP_STRUCT__entry(
__field(int, adapter_nr )
__field(__u16, msg_nr )
__field(__u16, addr )
__field(__u16, flags )
__field(__u16, len )
__dynamic_array(__u8, buf, msg->len) ),
TP_fast_assign(
__entry->adapter_nr = adap->nr;
__entry->msg_nr = num;
__entry->addr = msg->addr;
__entry->flags = msg->flags;
__entry->len = msg->len;
memcpy(__get_dynamic_array(buf), msg->buf, msg->len);
),
TP_printk("i2c-%d #%u a=%03x f=%04x l=%u [%*phD]",
__entry->adapter_nr,
__entry->msg_nr,
__entry->addr,
__entry->flags,
__entry->len,
__entry->len, __get_dynamic_array(buf)
),
i2c_transfer_trace_reg,
i2c_transfer_trace_unreg);

/*
* __i2c_transfer() read request
*/
TRACE_EVENT_FN(i2c_read,
TP_PROTO(const struct i2c_adapter *adap, const struct i2c_msg *msg,
int num),
TP_ARGS(adap, msg, num),
TP_STRUCT__entry(
__field(int, adapter_nr )
__field(__u16, msg_nr )
__field(__u16, addr )
__field(__u16, flags )
__field(__u16, len )
),
TP_fast_assign(
__entry->adapter_nr = adap->nr;
__entry->msg_nr = num;
__entry->addr = msg->addr;
__entry->flags = msg->flags;
__entry->len = msg->len;
),
TP_printk("i2c-%d #%u a=%03x f=%04x l=%u",
__entry->adapter_nr,
__entry->msg_nr,
__entry->addr,
__entry->flags,
__entry->len
),
i2c_transfer_trace_reg,
i2c_transfer_trace_unreg);

/*
* __i2c_transfer() read reply
*/
TRACE_EVENT_FN(i2c_reply,
TP_PROTO(const struct i2c_adapter *adap, const struct i2c_msg *msg,
int num),
TP_ARGS(adap, msg, num),
TP_STRUCT__entry(
__field(int, adapter_nr )
__field(__u16, msg_nr )
__field(__u16, addr )
__field(__u16, flags )
__field(__u16, len )
__dynamic_array(__u8, buf, msg->len) ),
TP_fast_assign(
__entry->adapter_nr = adap->nr;
__entry->msg_nr = num;
__entry->addr = msg->addr;
__entry->flags = msg->flags;
__entry->len = msg->len;
memcpy(__get_dynamic_array(buf), msg->buf, msg->len);
),
TP_printk("i2c-%d #%u a=%03x f=%04x l=%u [%*phD]",
__entry->adapter_nr,
__entry->msg_nr,
__entry->addr,
__entry->flags,
__entry->len,
__entry->len, __get_dynamic_array(buf)
),
i2c_transfer_trace_reg,
i2c_transfer_trace_unreg);

/*
* __i2c_transfer() result
*/
TRACE_EVENT_FN(i2c_result,
TP_PROTO(const struct i2c_adapter *adap, int num, int ret),
TP_ARGS(adap, num, ret),
TP_STRUCT__entry(
__field(int, adapter_nr )
__field(__u16, nr_msgs )
__field(__s16, ret )
),
TP_fast_assign(
__entry->adapter_nr = adap->nr;
__entry->nr_msgs = num;
__entry->ret = ret;
),
TP_printk("i2c-%d n=%u ret=%d",
__entry->adapter_nr,
__entry->nr_msgs,
__entry->ret
),
i2c_transfer_trace_reg,
i2c_transfer_trace_unreg);

#endif /* _TRACE_I2C_H */

/* This part must be outside protection */
#include <trace/define_trace.h>

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