* [PATCH WIP v2] i2c: add tracepoints to aid debugging in i2c-core-base
@ 2025-08-17 7:55 Mohammad Gomaa
2025-08-18 7:19 ` Dan Carpenter
2025-08-19 16:09 ` Steven Rostedt
0 siblings, 2 replies; 3+ messages in thread
From: Mohammad Gomaa @ 2025-08-17 7:55 UTC (permalink / raw)
To: Wolfram Sang, Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers
Cc: linux-i2c, linux-kernel, linux-trace-kernel, kenalba, hbarnor,
rayxu, Mohammad Gomaa
Add tracepoints to i2c-core-base.c file to help trace
and debug I2C device probe failures.
The new trace points are:
- i2c_device_probe_debug: records non-failure routines
e.g. IRQ 0.
- i2c_device_probe_complete: records failed & successful
probbes with appropriate trace message.
To support operation of these tracepoints an enum
was added that stores log message for debug and failure.
Signed-off-by: Mohammad Gomaa <midomaxgomaa@gmail.com>
---
Hello,
This patch adds tracepoints to i2c-core-base to aid with debugging I2C probing failrues.
The motivation for this comes from my work in Google Summer of Code (GSoC) 2025:
"ChromeOS Platform Input Device Quality Monitoring"
https://summerofcode.withgoogle.com/programs/2025/projects/uCdIgK7K
This is my first submission to the Linux kernel, so any feedback is welcome.
---
Changes in v2:
- Refactored i2c_device_probe_failed to i2c_device_probe_complete
to support both successful and failed probes.
- Fixed formatting for TRACE_EVENT().
- Used enum instead of string variable for "reason".
- Link to v1: https://lore.kernel.org/r/20250806-refactor-add-i2c-tracepoints-v1-1-d1d39bd6fb57@gmail.com
---
drivers/i2c/i2c-core-base.c | 63 ++++++++++++++++++++++++--------
include/trace/events/i2c.h | 88 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 137 insertions(+), 14 deletions(-)
diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index ecca8c006b020379fb53293b20ab09ba25314609..7ca22759d26e85ee51bea60f414ed014e9bcec40 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -495,6 +495,8 @@ static int i2c_device_probe(struct device *dev)
struct i2c_driver *driver;
bool do_power_on;
int status;
+ int err_reason;
+ bool has_id_table, has_acpi_match, has_of_match;
if (!client)
return 0;
@@ -509,38 +511,54 @@ static int i2c_device_probe(struct device *dev)
/* Keep adapter active when Host Notify is required */
pm_runtime_get_sync(&client->adapter->dev);
irq = i2c_smbus_host_notify_to_irq(client);
+ err_reason = I2C_TRACE_REASON_HOST_NOTIFY;
} else if (is_of_node(fwnode)) {
irq = fwnode_irq_get_byname(fwnode, "irq");
if (irq == -EINVAL || irq == -ENODATA)
irq = fwnode_irq_get(fwnode, 0);
+ err_reason = I2C_TRACE_REASON_FROM_OF;
} else if (is_acpi_device_node(fwnode)) {
bool wake_capable;
irq = i2c_acpi_get_irq(client, &wake_capable);
if (irq > 0 && wake_capable)
client->flags |= I2C_CLIENT_WAKE;
+ err_reason = I2C_TRACE_REASON_FROM_ACPI;
}
if (irq == -EPROBE_DEFER) {
status = dev_err_probe(dev, irq, "can't get irq\n");
+ err_reason = I2C_TRACE_REASON_EPROBE_DEFER_IRQ;
goto put_sync_adapter;
}
- if (irq < 0)
+ if (irq < 0) {
+ trace_i2c_device_probe_debug(dev, err_reason);
irq = 0;
+ }
client->irq = irq;
}
driver = to_i2c_driver(dev->driver);
+ has_id_table = driver->id_table;
+ has_acpi_match = acpi_driver_match_device(dev, dev->driver);
+ has_of_match = i2c_of_match_device(dev->driver->of_match_table, client);
+
+ if (!has_id_table)
+ trace_i2c_device_probe_debug(dev, I2C_TRACE_REASON_NO_I2C_ID_TABLE);
+ if (!has_acpi_match)
+ trace_i2c_device_probe_debug(dev, I2C_TRACE_REASON_ACPI_ID_MISMATCH);
+ if (!has_of_match)
+ trace_i2c_device_probe_debug(dev, I2C_TRACE_REASON_OF_ID_MISMATCH);
+
/*
* An I2C ID table is not mandatory, if and only if, a suitable OF
* or ACPI ID table is supplied for the probing device.
*/
- if (!driver->id_table &&
- !acpi_driver_match_device(dev, dev->driver) &&
- !i2c_of_match_device(dev->driver->of_match_table, client)) {
+ if (!has_id_table && !has_acpi_match && !has_of_match) {
status = -ENODEV;
+ err_reason = I2C_TRACE_REASON_NO_ID_MATCH;
goto put_sync_adapter;
}
@@ -550,47 +568,60 @@ static int i2c_device_probe(struct device *dev)
wakeirq = fwnode_irq_get_byname(fwnode, "wakeup");
if (wakeirq == -EPROBE_DEFER) {
status = dev_err_probe(dev, wakeirq, "can't get wakeirq\n");
+ err_reason = I2C_TRACE_REASON_EPROBE_DEFER_WAKEIRQ;
goto put_sync_adapter;
}
device_init_wakeup(&client->dev, true);
- if (wakeirq > 0 && wakeirq != client->irq)
+ if (wakeirq > 0 && wakeirq != client->irq) {
status = dev_pm_set_dedicated_wake_irq(dev, wakeirq);
- else if (client->irq > 0)
+ err_reason = I2C_TRACE_REASON_SET_DED_WAKE_FAILED;
+ } else if (client->irq > 0) {
status = dev_pm_set_wake_irq(dev, client->irq);
- else
+ err_reason = I2C_TRACE_REASON_SET_WAKE_FAILED;
+ } else {
status = 0;
+ err_reason = I2C_TRACE_REASON_NO_IRQ;
+ }
- if (status)
+ if (status) {
dev_warn(&client->dev, "failed to set up wakeup irq\n");
+ trace_i2c_device_probe_debug(&client->dev, err_reason);
+ }
}
dev_dbg(dev, "probe\n");
status = of_clk_set_defaults(to_of_node(fwnode), false);
- if (status < 0)
+ if (status < 0) {
+ err_reason = I2C_TRACE_REASON_SET_DEF_CLOCKS;
goto err_clear_wakeup_irq;
-
+ }
do_power_on = !i2c_acpi_waive_d0_probe(dev);
status = dev_pm_domain_attach(&client->dev, do_power_on ? PD_FLAG_ATTACH_POWER_ON : 0);
- if (status)
+ if (status) {
+ err_reason = I2C_TRACE_REASON_ATTACH_PM_DOMAIN;
goto err_clear_wakeup_irq;
-
+ }
client->devres_group_id = devres_open_group(&client->dev, NULL,
GFP_KERNEL);
if (!client->devres_group_id) {
status = -ENOMEM;
+ err_reason = I2C_TRACE_REASON_OPEN_DEVRES_GROUP;
goto err_detach_pm_domain;
}
client->debugfs = debugfs_create_dir(dev_name(&client->dev),
client->adapter->debugfs);
- if (driver->probe)
+ if (driver->probe) {
status = driver->probe(client);
- else
+ err_reason = I2C_TRACE_REASON_PROBE_FAILED;
+ } else {
status = -EINVAL;
+ err_reason = I2C_TRACE_REASON_NO_PROBE;
+ }
/*
* Note that we are not closing the devres group opened above so
@@ -603,6 +634,8 @@ static int i2c_device_probe(struct device *dev)
if (status)
goto err_release_driver_resources;
+ trace_i2c_device_probe_complete(&client->dev, status, err_reason);
+
return 0;
err_release_driver_resources:
@@ -617,6 +650,8 @@ static int i2c_device_probe(struct device *dev)
if (client->flags & I2C_CLIENT_HOST_NOTIFY)
pm_runtime_put_sync(&client->adapter->dev);
+ trace_i2c_device_probe_complete(&client->dev, status, err_reason);
+
return status;
}
diff --git a/include/trace/events/i2c.h b/include/trace/events/i2c.h
index 142a23c6593c611de9abc2a89a146b95550b23cd..b00650ceba0a96a7cc538991ce5d5a45ea553715 100644
--- a/include/trace/events/i2c.h
+++ b/include/trace/events/i2c.h
@@ -16,6 +16,94 @@
/*
* drivers/i2c/i2c-core-base.c
*/
+#ifndef I2C_TRACE_REASON_ENUM_DEFINED
+#define I2C_TRACE_REASON_ENUM_DEFINED
+
+#define I2C_TRACE_REASON \
+EM(HOST_NOTIFY, "IRQ 0: could not get irq from Host Notify") \
+EM(FROM_OF, "IRQ 0: could not get irq from OF") \
+EM(FROM_ACPI, "IRQ 0: could not get irq from ACPI") \
+EM(EPROBE_DEFER_IRQ, "IRQ 0: could not get IRQ due to EPROBE_DEFER") \
+EM(NO_I2C_ID_TABLE, "no I2C ID table") \
+EM(ACPI_ID_MISMATCH, "ACPI ID table mismatch") \
+EM(OF_ID_MISMATCH, "OF ID table mismatch") \
+EM(NO_ID_MATCH, "no I2C ID table and no ACPI/OF match") \
+EM(EPROBE_DEFER_WAKEIRQ, "get wake IRQ due to EPROBE_DEFER") \
+EM(SET_DED_WAKE_FAILED, "failed to set dedicated wakeup IRQ") \
+EM(SET_WAKE_FAILED, "failed to set wakeup IRQ") \
+EM(NO_IRQ, "no IRQ") \
+EM(SET_DEF_CLOCKS, "set default clocks") \
+EM(ATTACH_PM_DOMAIN, "attach PM domain") \
+EM(OPEN_DEVRES_GROUP, "open devres group") \
+EM(PROBE_FAILED, "specific driver probe failed") \
+EMe(NO_PROBE, "no probe defined")
+
+#undef EM
+#undef EMe
+#define EM(a, b) I2C_TRACE_REASON_##a,
+#define EMe(a, b) I2C_TRACE_REASON_##a
+enum {
+ I2C_TRACE_REASON
+};
+
+#undef EM
+#undef EMe
+#define EM(a, b) TRACE_DEFINE_ENUM(I2C_TRACE_REASON_##a);
+#define EMe(a, b) TRACE_DEFINE_ENUM(I2C_TRACE_REASON_##a);
+I2C_TRACE_REASON
+
+#undef EM
+#undef EMe
+#define EM(a, b) { I2C_TRACE_REASON_##a, b },
+#define EMe(a, b) { I2C_TRACE_REASON_##a, b }
+
+#endif /* I2C_TRACE_REASON_ENUM_DEFINED */
+
+TRACE_EVENT(i2c_device_probe_debug,
+
+ TP_PROTO(struct device *dev, int err_reason),
+
+ TP_ARGS(dev, err_reason),
+
+ TP_STRUCT__entry(
+ __string( devname, dev_name(dev) )
+ __field( int, err_reason )
+ ),
+
+ TP_fast_assign(
+ __assign_str(devname);
+ __entry->err_reason = err_reason;
+ ),
+
+ TP_printk("device=%s: %s",
+ __get_str(devname),
+ __print_symbolic(__entry->err_reason, I2C_TRACE_REASON))
+);
+
+TRACE_EVENT(i2c_device_probe_complete,
+
+ TP_PROTO(struct device *dev, int status, int err_reason),
+
+ TP_ARGS(dev, status, err_reason),
+
+ TP_STRUCT__entry(
+ __string( dev_name, dev_name(dev) )
+ __field( int, status )
+ __field( int, err_reason )
+ ),
+
+ TP_fast_assign(
+ __assign_str(dev_name);
+ __entry->status = status;
+ __entry->err_reason = err_reason;
+ ),
+
+ TP_printk("%s probe %s: %s",
+ __get_str(dev_name),
+ __entry->status ? "failed" : "succeeded",
+ __entry->status ? __print_symbolic(__entry->err_reason, I2C_TRACE_REASON) : "")
+);
+
extern int i2c_transfer_trace_reg(void);
extern void i2c_transfer_trace_unreg(void);
---
base-commit: 7e161a991ea71e6ec526abc8f40c6852ebe3d946
change-id: 20250806-refactor-add-i2c-tracepoints-b6e2b92d4cd9
Best regards,
--
Mohammad Gomaa <midomaxgomaa@gmail.com>
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH WIP v2] i2c: add tracepoints to aid debugging in i2c-core-base
2025-08-17 7:55 [PATCH WIP v2] i2c: add tracepoints to aid debugging in i2c-core-base Mohammad Gomaa
@ 2025-08-18 7:19 ` Dan Carpenter
2025-08-19 16:09 ` Steven Rostedt
1 sibling, 0 replies; 3+ messages in thread
From: Dan Carpenter @ 2025-08-18 7:19 UTC (permalink / raw)
To: oe-kbuild, Mohammad Gomaa, Wolfram Sang, Steven Rostedt,
Masami Hiramatsu, Mathieu Desnoyers
Cc: lkp, oe-kbuild-all, linux-i2c, linux-kernel, linux-trace-kernel,
kenalba, hbarnor, rayxu, Mohammad Gomaa
Hi Mohammad,
kernel test robot noticed the following build warnings:
url: https://github.com/intel-lab-lkp/linux/commits/Mohammad-Gomaa/i2c-add-tracepoints-to-aid-debugging-in-i2c-core-base/20250817-155936
base: 7e161a991ea71e6ec526abc8f40c6852ebe3d946
patch link: https://lore.kernel.org/r/20250817-refactor-add-i2c-tracepoints-v2-1-c0bad299e02e%40gmail.com
patch subject: [PATCH WIP v2] i2c: add tracepoints to aid debugging in i2c-core-base
config: x86_64-randconfig-161-20250818 (https://download.01.org/0day-ci/archive/20250818/202508181525.GKAXMVYv-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14+deb12u1) 12.2.0
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
| Closes: https://lore.kernel.org/r/202508181525.GKAXMVYv-lkp@intel.com/
smatch warnings:
drivers/i2c/i2c-core-base.c:535 i2c_device_probe() error: uninitialized symbol 'err_reason'.
vim +/err_reason +535 drivers/i2c/i2c-core-base.c
f37dd80ac2a67e4 drivers/i2c/i2c-core.c David Brownell 2007-02-13 491 static int i2c_device_probe(struct device *dev)
^1da177e4c3f415 drivers/i2c/i2c-core.c Linus Torvalds 2005-04-16 492 {
5763a474c887d4a drivers/i2c/i2c-core-base.c Andy Shevchenko 2025-04-16 493 struct fwnode_handle *fwnode = dev_fwnode(dev);
51298d1257b9f0a drivers/i2c/i2c-core.c Jean Delvare 2009-09-18 494 struct i2c_client *client = i2c_verify_client(dev);
51298d1257b9f0a drivers/i2c/i2c-core.c Jean Delvare 2009-09-18 495 struct i2c_driver *driver;
79ece9b292af6b0 drivers/i2c/i2c-core-base.c Ricardo Ribalda 2022-11-14 496 bool do_power_on;
50c3304a5e1e521 drivers/i2c/i2c-core.c Hans Verkuil 2008-03-12 497 int status;
dc94c3bf033524a drivers/i2c/i2c-core-base.c Mohammad Gomaa 2025-08-17 498 int err_reason;
dc94c3bf033524a drivers/i2c/i2c-core-base.c Mohammad Gomaa 2025-08-17 499 bool has_id_table, has_acpi_match, has_of_match;
7b4fbc50fabb810 drivers/i2c/i2c-core.c David Brownell 2007-05-01 500
51298d1257b9f0a drivers/i2c/i2c-core.c Jean Delvare 2009-09-18 501 if (!client)
51298d1257b9f0a drivers/i2c/i2c-core.c Jean Delvare 2009-09-18 502 return 0;
51298d1257b9f0a drivers/i2c/i2c-core.c Jean Delvare 2009-09-18 503
6e76cb7dfd34a2e drivers/i2c/i2c-core-base.c Charles Keepax 2019-06-27 504 client->irq = client->init_irq;
6e76cb7dfd34a2e drivers/i2c/i2c-core-base.c Charles Keepax 2019-06-27 505
0c2a34937f7e4c4 drivers/i2c/i2c-core-base.c Wolfram Sang 2020-06-30 506 if (!client->irq) {
845c877009cf014 drivers/i2c/i2c-core.c Mika Westerberg 2015-05-06 507 int irq = -ENOENT;
845c877009cf014 drivers/i2c/i2c-core.c Mika Westerberg 2015-05-06 508
331c34255293cd0 drivers/i2c/i2c-core.c Dmitry Torokhov 2017-01-04 509 if (client->flags & I2C_CLIENT_HOST_NOTIFY) {
331c34255293cd0 drivers/i2c/i2c-core.c Dmitry Torokhov 2017-01-04 510 dev_dbg(dev, "Using Host Notify IRQ\n");
72bfcee11cf8950 drivers/i2c/i2c-core-base.c Jarkko Nikula 2019-04-30 511 /* Keep adapter active when Host Notify is required */
72bfcee11cf8950 drivers/i2c/i2c-core-base.c Jarkko Nikula 2019-04-30 512 pm_runtime_get_sync(&client->adapter->dev);
331c34255293cd0 drivers/i2c/i2c-core.c Dmitry Torokhov 2017-01-04 513 irq = i2c_smbus_host_notify_to_irq(client);
dc94c3bf033524a drivers/i2c/i2c-core-base.c Mohammad Gomaa 2025-08-17 514 err_reason = I2C_TRACE_REASON_HOST_NOTIFY;
5763a474c887d4a drivers/i2c/i2c-core-base.c Andy Shevchenko 2025-04-16 515 } else if (is_of_node(fwnode)) {
5d9424b00b577b6 drivers/i2c/i2c-core-base.c Andy Shevchenko 2025-04-16 516 irq = fwnode_irq_get_byname(fwnode, "irq");
3fffd1283927342 drivers/i2c/i2c-core.c Dmitry Torokhov 2015-08-17 517 if (irq == -EINVAL || irq == -ENODATA)
5d9424b00b577b6 drivers/i2c/i2c-core-base.c Andy Shevchenko 2025-04-16 518 irq = fwnode_irq_get(fwnode, 0);
dc94c3bf033524a drivers/i2c/i2c-core-base.c Mohammad Gomaa 2025-08-17 519 err_reason = I2C_TRACE_REASON_FROM_OF;
5763a474c887d4a drivers/i2c/i2c-core-base.c Andy Shevchenko 2025-04-16 520 } else if (is_acpi_device_node(fwnode)) {
b38f2d5d9615cf9 drivers/i2c/i2c-core-base.c Raul E Rangel 2022-09-29 521 bool wake_capable;
b38f2d5d9615cf9 drivers/i2c/i2c-core-base.c Raul E Rangel 2022-09-29 522
b38f2d5d9615cf9 drivers/i2c/i2c-core-base.c Raul E Rangel 2022-09-29 523 irq = i2c_acpi_get_irq(client, &wake_capable);
b38f2d5d9615cf9 drivers/i2c/i2c-core-base.c Raul E Rangel 2022-09-29 524 if (irq > 0 && wake_capable)
b38f2d5d9615cf9 drivers/i2c/i2c-core-base.c Raul E Rangel 2022-09-29 525 client->flags |= I2C_CLIENT_WAKE;
dc94c3bf033524a drivers/i2c/i2c-core-base.c Mohammad Gomaa 2025-08-17 526 err_reason = I2C_TRACE_REASON_FROM_ACPI;
3fffd1283927342 drivers/i2c/i2c-core.c Dmitry Torokhov 2015-08-17 527 }
err_reason not set on else { path.
3c3dd56f760da05 drivers/i2c/i2c-core-base.c Alain Volmat 2020-04-30 528 if (irq == -EPROBE_DEFER) {
5c52473b4496b35 drivers/i2c/i2c-core-base.c Xu Yang 2025-05-07 529 status = dev_err_probe(dev, irq, "can't get irq\n");
dc94c3bf033524a drivers/i2c/i2c-core-base.c Mohammad Gomaa 2025-08-17 530 err_reason = I2C_TRACE_REASON_EPROBE_DEFER_IRQ;
3c3dd56f760da05 drivers/i2c/i2c-core-base.c Alain Volmat 2020-04-30 531 goto put_sync_adapter;
3c3dd56f760da05 drivers/i2c/i2c-core-base.c Alain Volmat 2020-04-30 532 }
331c34255293cd0 drivers/i2c/i2c-core.c Dmitry Torokhov 2017-01-04 533
dc94c3bf033524a drivers/i2c/i2c-core-base.c Mohammad Gomaa 2025-08-17 534 if (irq < 0) {
dc94c3bf033524a drivers/i2c/i2c-core-base.c Mohammad Gomaa 2025-08-17 @535 trace_i2c_device_probe_debug(dev, err_reason);
^^^^^^^^^^
6f34be7400c68d3 drivers/i2c/i2c-core.c Geert Uytterhoeven 2014-11-17 536 irq = 0;
dc94c3bf033524a drivers/i2c/i2c-core-base.c Mohammad Gomaa 2025-08-17 537 }
2fd36c55264926e drivers/i2c/i2c-core.c Laurent Pinchart 2014-10-30 538
2fd36c55264926e drivers/i2c/i2c-core.c Laurent Pinchart 2014-10-30 539 client->irq = irq;
2fd36c55264926e drivers/i2c/i2c-core.c Laurent Pinchart 2014-10-30 540 }
2fd36c55264926e drivers/i2c/i2c-core.c Laurent Pinchart 2014-10-30 541
0c2a34937f7e4c4 drivers/i2c/i2c-core-base.c Wolfram Sang 2020-06-30 542 driver = to_i2c_driver(dev->driver);
0c2a34937f7e4c4 drivers/i2c/i2c-core-base.c Wolfram Sang 2020-06-30 543
dc94c3bf033524a drivers/i2c/i2c-core-base.c Mohammad Gomaa 2025-08-17 544 has_id_table = driver->id_table;
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH WIP v2] i2c: add tracepoints to aid debugging in i2c-core-base
2025-08-17 7:55 [PATCH WIP v2] i2c: add tracepoints to aid debugging in i2c-core-base Mohammad Gomaa
2025-08-18 7:19 ` Dan Carpenter
@ 2025-08-19 16:09 ` Steven Rostedt
1 sibling, 0 replies; 3+ messages in thread
From: Steven Rostedt @ 2025-08-19 16:09 UTC (permalink / raw)
To: Mohammad Gomaa
Cc: Wolfram Sang, Masami Hiramatsu, Mathieu Desnoyers, linux-i2c,
linux-kernel, linux-trace-kernel, kenalba, hbarnor, rayxu
On Sun, 17 Aug 2025 10:55:14 +0300
Mohammad Gomaa <midomaxgomaa@gmail.com> wrote:
> Hello,
>
> This patch adds tracepoints to i2c-core-base to aid with debugging I2C probing failrues.
>
> The motivation for this comes from my work in Google Summer of Code (GSoC) 2025:
> "ChromeOS Platform Input Device Quality Monitoring"
> https://summerofcode.withgoogle.com/programs/2025/projects/uCdIgK7K
>
> This is my first submission to the Linux kernel, so any feedback is welcome.
Welcome Mohammad!
> driver = to_i2c_driver(dev->driver);
>
I'll let those that own this code discuss the merits of this, and if
there's a better way to achieve this. But I'll comment only on the tracing
aspect of this change.
> + has_id_table = driver->id_table;
> + has_acpi_match = acpi_driver_match_device(dev, dev->driver);
> + has_of_match = i2c_of_match_device(dev->driver->of_match_table, client);
> +
> + if (!has_id_table)
> + trace_i2c_device_probe_debug(dev, I2C_TRACE_REASON_NO_I2C_ID_TABLE);
> + if (!has_acpi_match)
> + trace_i2c_device_probe_debug(dev, I2C_TRACE_REASON_ACPI_ID_MISMATCH);
> + if (!has_of_match)
> + trace_i2c_device_probe_debug(dev, I2C_TRACE_REASON_OF_ID_MISMATCH);
The above adds if statements into the running code when tracing is disabled
and this causes pressure on the branch prediction and should be avoided. To
avoid this, you could use the trace_<tracepoint>_enabled() helper:
if (trace_i2c_device_probe_debug_enabled()) {
has_id_table = driver->id_table;
has_acpi_match = acpi_driver_match_device(dev, dev->driver);
has_of_match = i2c_of_match_device(dev->driver->of_match_table, client);
if (!has_id_table)
trace_i2c_device_probe_debug(dev, I2C_TRACE_REASON_NO_I2C_ID_TABLE);
if (!has_acpi_match)
trace_i2c_device_probe_debug(dev, I2C_TRACE_REASON_ACPI_ID_MISMATCH);
if (!has_of_match)
trace_i2c_device_probe_debug(dev, I2C_TRACE_REASON_OF_ID_MISMATCH);
}
But I suspect there's a better way to record this information. I just
wanted to inform you on the trace_<tracepoint>_enabled() logic. What it
does is to add a static branch (jump label) where there's no "if"
statement. It's either a nop that skips this code altogether, or it's a jmp
to the code that will do the logic as well as the tracing and then jump
back to where it left off.
It's much more efficient to use this and it doesn't add anything to the
branch prediction cache.
-- Steve
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2025-08-19 16:09 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz follow: Atom feed
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2025-08-17 7:55 [PATCH WIP v2] i2c: add tracepoints to aid debugging in i2c-core-base Mohammad Gomaa
2025-08-18 7:19 ` Dan Carpenter
2025-08-19 16:09 ` Steven Rostedt
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