i2c: Add message transfer tracepoints for SMBUS [ver #2]

The SMBUS tracepoints 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:

         ... smbus_read: i2c-0 a=051 f=0000 c=fa BYTE_DATA
         ... smbus_reply: i2c-0 a=051 f=0000 c=fa BYTE_DATA l=1 [39]
         ... smbus_result: i2c-0 a=051 f=0000 c=fa BYTE_DATA rd res=0

formatted as:

	i2c-<adapter-nr>
	a=<addr>
	f=<flags>
	c=<command>
	<protocol-name>
	<rd|wr>
	res=<result>
	l=<data-len>
	[<data-block>]

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

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

Note that this shares the same filter and enablement as i2c.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

1 files changed, 20 insertions, 3 deletions

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index bdedbee85c01..7c7f4b856bad 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -2565,6 +2565,14 @@ s32 i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr, unsigned short flags,
         int try;
         s32 res;
 
+        /* If enabled, the following two tracepoints are conditional on
+         * read_write and protocol.
+         */
+        trace_smbus_write(adapter, addr, flags, read_write,
+                          command, protocol, data);
+        trace_smbus_read(adapter, addr, flags, read_write,
+                         command, protocol);
+
         flags &= I2C_M_TEN | I2C_CLIENT_PEC | I2C_CLIENT_SCCB;
 
         if (adapter->algo->smbus_xfer) {
@@ -2585,15 +2593,24 @@ s32 i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr, unsigned short flags,
                 i2c_unlock_adapter(adapter);
 
                 if (res != -EOPNOTSUPP || !adapter->algo->master_xfer)
-                        return res;
+                        goto trace;
                 /*
                  * Fall back to i2c_smbus_xfer_emulated if the adapter doesn't
                  * implement native support for the SMBus operation.
                  */
         }
 
-        return i2c_smbus_xfer_emulated(adapter, addr, flags, read_write,
-                                       command, protocol, data);
+        res = i2c_smbus_xfer_emulated(adapter, addr, flags, read_write,
+                                      command, protocol, data);
+
+trace:
+        /* If enabled, the reply tracepoint is conditional on read_write. */
+        trace_smbus_reply(adapter, addr, flags, read_write,
+                          command, protocol, data);
+        trace_smbus_result(adapter, addr, flags, read_write,
+                           command, protocol, res);
+
+        return res;
 }
 EXPORT_SYMBOL(i2c_smbus_xfer);