Patchwork [1/2] i2c: Add message transfer tracepoints for I2C

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Submitter David Howells
Date Jan. 9, 2014, 9:49 p.m.
Message ID <20140109214954.25590.73057.stgit@warthog.procyon.org.uk>
Download mbox | patch
Permalink /patch/308958/
State Changes Requested
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Comments

David Howells - Jan. 9, 2014, 9:49 p.m.
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/i2c_transfer/enable

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

	... i2c_write: i2c-5 #0 f=00 a=44 l=2 [0214]
	... i2c_read: i2c-5 #1 f=01 a=44 l=4
	... i2c_reply: i2c-5 #1 f=01 a=44 l=4 [33000000]
	... i2c_result: i2c-5 n=2 ret=2

formatted as:

	i2c-<adapter-nr>
	#<message-array-index>
	f=<flags>
	a=<addr>
	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>
---

 drivers/i2c/i2c-core.c     |   37 +++++++++++
 include/trace/events/i2c.h |  150 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 187 insertions(+)
 create mode 100644 include/trace/events/i2c.h


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Wolfram Sang - Jan. 22, 2014, 7:09 p.m.
On Thu, Jan 09, 2014 at 09:49:54PM +0000, David Howells wrote:
> 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/i2c_transfer/enable
> 
> and will dump messages that can be viewed in /sys/kernel/debug/tracing/trace
> that look like:
> 
> 	... i2c_write: i2c-5 #0 f=00 a=44 l=2 [0214]
> 	... i2c_read: i2c-5 #1 f=01 a=44 l=4
> 	... i2c_reply: i2c-5 #1 f=01 a=44 l=4 [33000000]
> 	... i2c_result: i2c-5 n=2 ret=2
> 
> formatted as:
> 
> 	i2c-<adapter-nr>
> 	#<message-array-index>
> 	f=<flags>
> 	a=<addr>
> 	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>

Thanks for doing this, much appreciated. One of the first things I'll
review (and play with) next. But hey, has nobody else checked this out
by now? Tested-by or acks very welcome.

Thanks,

   Wolfram
Wolfram Sang - Feb. 18, 2014, 8:33 p.m.
Hi David,

On Thu, Jan 09, 2014 at 09:49:54PM +0000, David Howells wrote:
> 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/i2c_transfer/enable
> 
> and will dump messages that can be viewed in /sys/kernel/debug/tracing/trace
> that look like:
> 
> 	... i2c_write: i2c-5 #0 f=00 a=44 l=2 [0214]
> 	... i2c_read: i2c-5 #1 f=01 a=44 l=4
> 	... i2c_reply: i2c-5 #1 f=01 a=44 l=4 [33000000]
> 	... i2c_result: i2c-5 n=2 ret=2
> 
> formatted as:
> 
> 	i2c-<adapter-nr>
> 	#<message-array-index>
> 	f=<flags>
> 	a=<addr>
> 	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>

I like it very much, just have some comments about the format.

> +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 f=%02x a=%02x l=%u [%*phN]",

'flags' are u16 and the whole range is needed -> %04x

'addr' is u16 and either 7 or 10 bits are needed. The core does the
following when assigning names because it is possible to have devices
0x50 (7-bit) and 0x050 (10-bit) on the bus:

	/* For 10-bit clients, add an arbitrary offset to avoid collisions */
	dev_set_name(&client->dev, "%d-%04x", i2c_adapter_id(adap),
		     client->addr | ((client->flags & I2C_CLIENT_TEN)
				     ? 0xa000 : 0));

I don't know if this can be implemented. Actually, I don't think it
needs to be implemented since flags are printed, too. So, with this the
10-bit case is visible and for the address simply %03x should do.

And for the buffer: %*phN is difficult to read IMO. What about %*ph? Or
%*phD at least?

Thanks,

   Wolfram
David Howells - Feb. 27, 2014, 1:07 p.m.
Wolfram Sang <wsa@the-dreams.de> wrote:

> 'flags' are u16 and the whole range is needed -> %04x

Done.  Note that %02x does not preclude more digits, but I guess it's better
to have things line up.

> for the address simply %03x should do.

Done.

> And for the buffer: %*phN is difficult to read IMO. What about %*ph? Or
> %*phD at least?

My problem with that is that it increases the length of the output by 50% and
there's a hard limit on how much output we may produce.

David
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Wolfram Sang - Feb. 28, 2014, 9:17 p.m.
> > And for the buffer: %*phN is difficult to read IMO. What about %*ph? Or
> > %*phD at least?
> 
> My problem with that is that it increases the length of the output by 50% and
> there's a hard limit on how much output we may produce.

Is it PAGE_SIZE? How is this handled when the buffer is so big that the
limit will be reached anyhow? Note that it is really uncommon to
transfer kilobytes in one go via i2c. Usually, big transfers are split
up into smaller fragments, say 128-256 byte. So, for readability, I'd
still favour %*ph.
David Howells - March 1, 2014, 7:54 a.m.
Wolfram Sang <wsa@the-dreams.de> wrote:

> > > And for the buffer: %*phN is difficult to read IMO. What about %*ph? Or
> > > %*phD at least?
> > 
> > My problem with that is that it increases the length of the output by 50%
> > and there's a hard limit on how much output we may produce.
> 
> Is it PAGE_SIZE? How is this handled when the buffer is so big that the
> limit will be reached anyhow? Note that it is really uncommon to
> transfer kilobytes in one go via i2c. Usually, big transfers are split
> up into smaller fragments, say 128-256 byte. So, for readability, I'd
> still favour %*ph.

I was thinking that limited the size of the output field to 64 bytes.  But
reading vsprintf.c again, it appears it's actually the size of the binary blob
that it's converting to hex that's limited to 64 bytes.

I would prefer shorter lines - 128 bytes of hex still isn't entirely readable,
even with separators interpolated, but I'll add this.

David
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Patch

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index d74c0b34248e..c8b97490461d 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -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
@@ -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,
@@ -1680,6 +1695,7 @@  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
@@ -1710,6 +1726,19 @@  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++) {
@@ -1720,6 +1749,14 @@  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);
diff --git a/include/trace/events/i2c.h b/include/trace/events/i2c.h
new file mode 100644
index 000000000000..d30f008527b2
--- /dev/null
+++ b/include/trace/events/i2c.h
@@ -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 f=%02x a=%02x l=%u [%*phN]",
+			 __entry->adapter_nr,
+			 __entry->msg_nr,
+			 __entry->flags,
+			 __entry->addr,
+			 __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 f=%02x a=%02x l=%u",
+			 __entry->adapter_nr,
+			 __entry->msg_nr,
+			 __entry->flags,
+			 __entry->addr,
+			 __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 f=%02x a=%02x l=%u [%*phN]",
+			 __entry->adapter_nr,
+			 __entry->msg_nr,
+			 __entry->flags,
+			 __entry->addr,
+			 __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>