[PATCH] platform/chromeos: cros_ec: Use per-device lockdep key

[PATCH] platform/chromeos: cros_ec: Use per-device lockdep key

[Chen-Yu Tsai]

Lockdep reports a bogus possible deadlock on MT8192 Chromebooks due to
the following lock sequences:

1. lock(i2c_register_adapter) [1]; lock(&ec_dev->lock)
2. lock(&ec_dev->lock); lock(prepare_lock);

The actual dependency chains are much longer. The shortened version
looks somewhat like:

1. cros-ec-rpmsg on mtk-scp
   ec_dev->lock -> prepare_lock
2. In rt5682_i2c_probe() on native I2C bus:
   prepare_lock -> regmap->lock -> (possibly) i2c_adapter->bus_lock
3. In rt5682_i2c_probe() on native I2C bus:
   regmap->lock -> i2c_adapter->bus_lock
4. In sbs_probe() on cros-ec-i2c (passthrough) I2C bus on cros-ec
   i2c_adapter->bus_lock -> ec_dev->lock

While lockdep is correct that the shared lockdep classes have a circular
dependency, it is bogus because

  a) 2+3 happen on a native I2C bus
  b) 4 happens on the actual EC on ChromeOS devices
  c) 1 happens on the SCP coprocessor on MediaTek Chromebooks that just
     happen to expose a cros-ec interface, but do not have a passthrough
     I2C bus

In short, the "dependencies" are actually on different devices.

Setup a per-device lockdep key for cros_ec devices so lockdep can tell
the two instances apart. This helps with getting rid of the bogus
lockdep warning. For ChromeOS devices that only have one cros-ec
instance this doesn't change anything.

Also add a missing mutex_destroy, just to make the teardown complete.

[1] This is likely the per I2C bus lock with shared lockdep class

Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
---
 drivers/platform/chrome/cros_ec.c           | 14 +++++++++++---
 include/linux/platform_data/cros_ec_proto.h |  2 ++
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/drivers/platform/chrome/cros_ec.c b/drivers/platform/chrome/cros_ec.c
index ec733f683f34..4ae57820afd5 100644
--- a/drivers/platform/chrome/cros_ec.c
+++ b/drivers/platform/chrome/cros_ec.c
@@ -198,12 +198,14 @@ int cros_ec_register(struct cros_ec_device *ec_dev)
 	if (!ec_dev->dout)
 		return -ENOMEM;
 
+	lockdep_register_key(&ec_dev->lockdep_key);
 	mutex_init(&ec_dev->lock);
+	lockdep_set_class(&ec_dev->lock, &ec_dev->lockdep_key);
 
 	err = cros_ec_query_all(ec_dev);
 	if (err) {
 		dev_err(dev, "Cannot identify the EC: error %d\n", err);
-		return err;
+		goto destroy_mutex;
 	}
 
 	if (ec_dev->irq > 0) {
@@ -215,7 +217,7 @@ int cros_ec_register(struct cros_ec_device *ec_dev)
 		if (err) {
 			dev_err(dev, "Failed to request IRQ %d: %d\n",
 				ec_dev->irq, err);
-			return err;
+			goto destroy_mutex;
 		}
 	}
 
@@ -226,7 +228,8 @@ int cros_ec_register(struct cros_ec_device *ec_dev)
 	if (IS_ERR(ec_dev->ec)) {
 		dev_err(ec_dev->dev,
 			"Failed to create CrOS EC platform device\n");
-		return PTR_ERR(ec_dev->ec);
+		err = PTR_ERR(ec_dev->ec);
+		goto destroy_mutex;
 	}
 
 	if (ec_dev->max_passthru) {
@@ -292,6 +295,9 @@ int cros_ec_register(struct cros_ec_device *ec_dev)
 exit:
 	platform_device_unregister(ec_dev->ec);
 	platform_device_unregister(ec_dev->pd);
+destroy_mutex:
+	mutex_destroy(&ec_dev->lock);
+	lockdep_unregister_key(&ec_dev->lockdep_key);
 	return err;
 }
 EXPORT_SYMBOL(cros_ec_register);
@@ -309,6 +315,8 @@ void cros_ec_unregister(struct cros_ec_device *ec_dev)
 	if (ec_dev->pd)
 		platform_device_unregister(ec_dev->pd);
 	platform_device_unregister(ec_dev->ec);
+	mutex_destroy(&ec_dev->lock);
+	lockdep_unregister_key(&ec_dev->lockdep_key);
 }
 EXPORT_SYMBOL(cros_ec_unregister);
 
diff --git a/include/linux/platform_data/cros_ec_proto.h b/include/linux/platform_data/cros_ec_proto.h
index e43107e0bee1..677d2eae1692 100644
--- a/include/linux/platform_data/cros_ec_proto.h
+++ b/include/linux/platform_data/cros_ec_proto.h
@@ -9,6 +9,7 @@
 #define __LINUX_CROS_EC_PROTO_H
 
 #include <linux/device.h>
+#include <linux/lockdep_types.h>
 #include <linux/mutex.h>
 #include <linux/notifier.h>
 
@@ -160,6 +161,7 @@ struct cros_ec_device {
 			struct cros_ec_command *msg);
 	int (*pkt_xfer)(struct cros_ec_device *ec,
 			struct cros_ec_command *msg);
+	struct lock_class_key lockdep_key;
 	struct mutex lock;
 	u8 mkbp_event_supported;
 	bool host_sleep_v1;
-- 
2.39.0.314.g84b9a713c41-goog

Re: [PATCH] platform/chromeos: cros_ec: Use per-device lockdep key

[Tzung-Bi Shih]

On Fri, Jan 06, 2023 at 12:55:37PM +0800, Chen-Yu Tsai wrote:
> Lockdep reports a bogus possible deadlock on MT8192 Chromebooks due to
> the following lock sequences:
> 
> 1. lock(i2c_register_adapter) [1]; lock(&ec_dev->lock)
> 2. lock(&ec_dev->lock); lock(prepare_lock);
> 
> The actual dependency chains are much longer. The shortened version
> looks somewhat like:
> 
> 1. cros-ec-rpmsg on mtk-scp
>    ec_dev->lock -> prepare_lock
> 2. In rt5682_i2c_probe() on native I2C bus:
>    prepare_lock -> regmap->lock -> (possibly) i2c_adapter->bus_lock
> 3. In rt5682_i2c_probe() on native I2C bus:
>    regmap->lock -> i2c_adapter->bus_lock
> 4. In sbs_probe() on cros-ec-i2c (passthrough) I2C bus on cros-ec
>    i2c_adapter->bus_lock -> ec_dev->lock
> 
> While lockdep is correct that the shared lockdep classes have a circular
> dependency, it is bogus because
> 
>   a) 2+3 happen on a native I2C bus
>   b) 4 happens on the actual EC on ChromeOS devices
>   c) 1 happens on the SCP coprocessor on MediaTek Chromebooks that just
>      happen to expose a cros-ec interface, but do not have a passthrough
>      I2C bus
> 
> In short, the "dependencies" are actually on different devices.

Path of 4 looks weird to me.

Could you point out where sbs_probe() gets to acquire ec_dev->lock?

I may misunderstand: I thought there is no such I2C bus for passthrough
from kernel's point of view (as the bus and devices behind the EC).
See also [2].

[2]: https://elixir.bootlin.com/linux/v6.2-rc2/source/drivers/platform/chrome/cros_ec.c#L241


On a related note, for the commit title: s/chromeos/chrome/ if it gets
chance to have next version.

Re: [PATCH] platform/chromeos: cros_ec: Use per-device lockdep key

[Chen-Yu Tsai]

On Fri, Jan 6, 2023 at 5:08 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote:
>
> On Fri, Jan 06, 2023 at 12:55:37PM +0800, Chen-Yu Tsai wrote:
> > Lockdep reports a bogus possible deadlock on MT8192 Chromebooks due to
> > the following lock sequences:
> >
> > 1. lock(i2c_register_adapter) [1]; lock(&ec_dev->lock)
> > 2. lock(&ec_dev->lock); lock(prepare_lock);
> >
> > The actual dependency chains are much longer. The shortened version
> > looks somewhat like:
> >
> > 1. cros-ec-rpmsg on mtk-scp
> >    ec_dev->lock -> prepare_lock
> > 2. In rt5682_i2c_probe() on native I2C bus:
> >    prepare_lock -> regmap->lock -> (possibly) i2c_adapter->bus_lock
> > 3. In rt5682_i2c_probe() on native I2C bus:
> >    regmap->lock -> i2c_adapter->bus_lock
> > 4. In sbs_probe() on cros-ec-i2c (passthrough) I2C bus on cros-ec
> >    i2c_adapter->bus_lock -> ec_dev->lock
> >
> > While lockdep is correct that the shared lockdep classes have a circular
> > dependency, it is bogus because
> >
> >   a) 2+3 happen on a native I2C bus
> >   b) 4 happens on the actual EC on ChromeOS devices
> >   c) 1 happens on the SCP coprocessor on MediaTek Chromebooks that just
> >      happen to expose a cros-ec interface, but do not have a passthrough
> >      I2C bus
> >
> > In short, the "dependencies" are actually on different devices.
>
> Path of 4 looks weird to me.
>
> Could you point out where sbs_probe() gets to acquire ec_dev->lock?

sbs_probe() calls sbs_get_battery_presence_and_health(), which

  -> does an I2C transfer. This SBS instance is connected on the I2C bus
     on the EC, so the I2C transfer

     -> acquires i2c_adapter->bus_lock, and

       -> calls ec_i2c_xfer(), which

          -> calls cros_ec_cmd_xfer_status(), which

             -> calls cros_ec_cmd_xfer(), which

               -> acquires ec_dev->lock


> I may misunderstand: I thought there is no such I2C bus for passthrough
> from kernel's point of view (as the bus and devices behind the EC).
> See also [2].

It is an I2C adapter on the EC, also known as i2c-cros-ec-tunnel.
Passthrough probably isn't the right word.

> [2]: https://elixir.bootlin.com/linux/v6.2-rc2/source/drivers/platform/chrome/cros_ec.c#L241
>
>
> On a related note, for the commit title: s/chromeos/chrome/ if it gets
> chance to have next version.

OK.


Thanks
ChenYu

Re: [PATCH] platform/chromeos: cros_ec: Use per-device lockdep key

[Tzung-Bi Shih]

On Sat, Jan 07, 2023 at 01:43:57PM +0800, Chen-Yu Tsai wrote:
> On Fri, Jan 6, 2023 at 5:08 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote:
> >
> > On Fri, Jan 06, 2023 at 12:55:37PM +0800, Chen-Yu Tsai wrote:
> > > Lockdep reports a bogus possible deadlock on MT8192 Chromebooks due to
> > > the following lock sequences:
> > >
> > > 1. lock(i2c_register_adapter) [1]; lock(&ec_dev->lock)
> > > 2. lock(&ec_dev->lock); lock(prepare_lock);
> > >
> > > The actual dependency chains are much longer. The shortened version
> > > looks somewhat like:
> > >
> > > 1. cros-ec-rpmsg on mtk-scp
> > >    ec_dev->lock -> prepare_lock
> > > 2. In rt5682_i2c_probe() on native I2C bus:
> > >    prepare_lock -> regmap->lock -> (possibly) i2c_adapter->bus_lock
> > > 3. In rt5682_i2c_probe() on native I2C bus:
> > >    regmap->lock -> i2c_adapter->bus_lock
> > > 4. In sbs_probe() on cros-ec-i2c (passthrough) I2C bus on cros-ec
> > >    i2c_adapter->bus_lock -> ec_dev->lock
> > >
> > > While lockdep is correct that the shared lockdep classes have a circular
> > > dependency, it is bogus because
> > >
> > >   a) 2+3 happen on a native I2C bus
> > >   b) 4 happens on the actual EC on ChromeOS devices
> > >   c) 1 happens on the SCP coprocessor on MediaTek Chromebooks that just
> > >      happen to expose a cros-ec interface, but do not have a passthrough
> > >      I2C bus
> > >
> > > In short, the "dependencies" are actually on different devices.
> >
> > Path of 4 looks weird to me.
> >
> > Could you point out where sbs_probe() gets to acquire ec_dev->lock?
> 
> sbs_probe() calls sbs_get_battery_presence_and_health(), which
> 
>   -> does an I2C transfer. This SBS instance is connected on the I2C bus
>      on the EC, so the I2C transfer
> 
>      -> acquires i2c_adapter->bus_lock, and

I see.

Another question: the i2c_adapter here should be different from the native
I2C bus in 2 and 3.  Did they really form the circular dependencies?

Re: [PATCH] platform/chromeos: cros_ec: Use per-device lockdep key

[Chen-Yu Tsai]

On Mon, Jan 9, 2023 at 1:46 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote:
>
> On Sat, Jan 07, 2023 at 01:43:57PM +0800, Chen-Yu Tsai wrote:
> > On Fri, Jan 6, 2023 at 5:08 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote:
> > >
> > > On Fri, Jan 06, 2023 at 12:55:37PM +0800, Chen-Yu Tsai wrote:
> > > > Lockdep reports a bogus possible deadlock on MT8192 Chromebooks due to
> > > > the following lock sequences:
> > > >
> > > > 1. lock(i2c_register_adapter) [1]; lock(&ec_dev->lock)
> > > > 2. lock(&ec_dev->lock); lock(prepare_lock);
> > > >
> > > > The actual dependency chains are much longer. The shortened version
> > > > looks somewhat like:
> > > >
> > > > 1. cros-ec-rpmsg on mtk-scp
> > > >    ec_dev->lock -> prepare_lock
> > > > 2. In rt5682_i2c_probe() on native I2C bus:
> > > >    prepare_lock -> regmap->lock -> (possibly) i2c_adapter->bus_lock
> > > > 3. In rt5682_i2c_probe() on native I2C bus:
> > > >    regmap->lock -> i2c_adapter->bus_lock
> > > > 4. In sbs_probe() on cros-ec-i2c (passthrough) I2C bus on cros-ec
> > > >    i2c_adapter->bus_lock -> ec_dev->lock
> > > >
> > > > While lockdep is correct that the shared lockdep classes have a circular
> > > > dependency, it is bogus because
> > > >
> > > >   a) 2+3 happen on a native I2C bus
> > > >   b) 4 happens on the actual EC on ChromeOS devices
> > > >   c) 1 happens on the SCP coprocessor on MediaTek Chromebooks that just
> > > >      happen to expose a cros-ec interface, but do not have a passthrough
> > > >      I2C bus
> > > >
> > > > In short, the "dependencies" are actually on different devices.
> > >
> > > Path of 4 looks weird to me.
> > >
> > > Could you point out where sbs_probe() gets to acquire ec_dev->lock?
> >
> > sbs_probe() calls sbs_get_battery_presence_and_health(), which
> >
> >   -> does an I2C transfer. This SBS instance is connected on the I2C bus
> >      on the EC, so the I2C transfer
> >
> >      -> acquires i2c_adapter->bus_lock, and
>
> I see.
>
> Another question: the i2c_adapter here should be different from the native
> I2C bus in 2 and 3.  Did they really form the circular dependencies?

That's why it's a false positive. lockdep normally doesn't track individual
instances, only classes of locks. The class is declared as part of the
mutex_init() macro.

ChenYu

Re: [PATCH] platform/chromeos: cros_ec: Use per-device lockdep key

[Tzung-Bi Shih]

On Mon, Jan 09, 2023 at 02:19:38PM +0800, Chen-Yu Tsai wrote:
> On Mon, Jan 9, 2023 at 1:46 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote:
> >
> > On Sat, Jan 07, 2023 at 01:43:57PM +0800, Chen-Yu Tsai wrote:
> > > On Fri, Jan 6, 2023 at 5:08 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote:
> > > >
> > > > On Fri, Jan 06, 2023 at 12:55:37PM +0800, Chen-Yu Tsai wrote:
> > > > > Lockdep reports a bogus possible deadlock on MT8192 Chromebooks due to
> > > > > the following lock sequences:
> > > > >
> > > > > 1. lock(i2c_register_adapter) [1]; lock(&ec_dev->lock)
> > > > > 2. lock(&ec_dev->lock); lock(prepare_lock);
> > > > >
> > > > > The actual dependency chains are much longer. The shortened version
> > > > > looks somewhat like:
> > > > >
> > > > > 1. cros-ec-rpmsg on mtk-scp
> > > > >    ec_dev->lock -> prepare_lock
> > > > > 2. In rt5682_i2c_probe() on native I2C bus:
> > > > >    prepare_lock -> regmap->lock -> (possibly) i2c_adapter->bus_lock
> > > > > 3. In rt5682_i2c_probe() on native I2C bus:
> > > > >    regmap->lock -> i2c_adapter->bus_lock
> > > > > 4. In sbs_probe() on cros-ec-i2c (passthrough) I2C bus on cros-ec
> > > > >    i2c_adapter->bus_lock -> ec_dev->lock
> > > > >
> > > > > While lockdep is correct that the shared lockdep classes have a circular
> > > > > dependency, it is bogus because
> > > > >
> > > > >   a) 2+3 happen on a native I2C bus
> > > > >   b) 4 happens on the actual EC on ChromeOS devices
> > > > >   c) 1 happens on the SCP coprocessor on MediaTek Chromebooks that just
> > > > >      happen to expose a cros-ec interface, but do not have a passthrough
> > > > >      I2C bus
> > > > >
> > > > > In short, the "dependencies" are actually on different devices.
> > > >
> > > > Path of 4 looks weird to me.
> > > >
> > > > Could you point out where sbs_probe() gets to acquire ec_dev->lock?
> > >
> > > sbs_probe() calls sbs_get_battery_presence_and_health(), which
> > >
> > >   -> does an I2C transfer. This SBS instance is connected on the I2C bus
> > >      on the EC, so the I2C transfer
> > >
> > >      -> acquires i2c_adapter->bus_lock, and
> >
> > I see.
> >
> > Another question: the i2c_adapter here should be different from the native
> > I2C bus in 2 and 3.  Did they really form the circular dependencies?
> 
> That's why it's a false positive. lockdep normally doesn't track individual
> instances, only classes of locks. The class is declared as part of the
> mutex_init() macro.

Is the following understanding correct:
It has 2 ways to break the "fake" circular dependencies: separate lockdep key
for i2c_adapter vs. ec_dev.  The patch adopts the latter one because it has
limited impact for other I2C-related drivers.

Re: [PATCH] platform/chromeos: cros_ec: Use per-device lockdep key

[Chen-Yu Tsai]

On Mon, Jan 9, 2023 at 3:30 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote:
>
> On Mon, Jan 09, 2023 at 02:19:38PM +0800, Chen-Yu Tsai wrote:
> > On Mon, Jan 9, 2023 at 1:46 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote:
> > >
> > > On Sat, Jan 07, 2023 at 01:43:57PM +0800, Chen-Yu Tsai wrote:
> > > > On Fri, Jan 6, 2023 at 5:08 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote:
> > > > >
> > > > > On Fri, Jan 06, 2023 at 12:55:37PM +0800, Chen-Yu Tsai wrote:
> > > > > > Lockdep reports a bogus possible deadlock on MT8192 Chromebooks due to
> > > > > > the following lock sequences:
> > > > > >
> > > > > > 1. lock(i2c_register_adapter) [1]; lock(&ec_dev->lock)
> > > > > > 2. lock(&ec_dev->lock); lock(prepare_lock);
> > > > > >
> > > > > > The actual dependency chains are much longer. The shortened version
> > > > > > looks somewhat like:
> > > > > >
> > > > > > 1. cros-ec-rpmsg on mtk-scp
> > > > > >    ec_dev->lock -> prepare_lock
> > > > > > 2. In rt5682_i2c_probe() on native I2C bus:
> > > > > >    prepare_lock -> regmap->lock -> (possibly) i2c_adapter->bus_lock
> > > > > > 3. In rt5682_i2c_probe() on native I2C bus:
> > > > > >    regmap->lock -> i2c_adapter->bus_lock
> > > > > > 4. In sbs_probe() on cros-ec-i2c (passthrough) I2C bus on cros-ec
> > > > > >    i2c_adapter->bus_lock -> ec_dev->lock
> > > > > >
> > > > > > While lockdep is correct that the shared lockdep classes have a circular
> > > > > > dependency, it is bogus because
> > > > > >
> > > > > >   a) 2+3 happen on a native I2C bus
> > > > > >   b) 4 happens on the actual EC on ChromeOS devices
> > > > > >   c) 1 happens on the SCP coprocessor on MediaTek Chromebooks that just
> > > > > >      happen to expose a cros-ec interface, but do not have a passthrough
> > > > > >      I2C bus
> > > > > >
> > > > > > In short, the "dependencies" are actually on different devices.
> > > > >
> > > > > Path of 4 looks weird to me.
> > > > >
> > > > > Could you point out where sbs_probe() gets to acquire ec_dev->lock?
> > > >
> > > > sbs_probe() calls sbs_get_battery_presence_and_health(), which
> > > >
> > > >   -> does an I2C transfer. This SBS instance is connected on the I2C bus
> > > >      on the EC, so the I2C transfer
> > > >
> > > >      -> acquires i2c_adapter->bus_lock, and
> > >
> > > I see.
> > >
> > > Another question: the i2c_adapter here should be different from the native
> > > I2C bus in 2 and 3.  Did they really form the circular dependencies?
> >
> > That's why it's a false positive. lockdep normally doesn't track individual
> > instances, only classes of locks. The class is declared as part of the
> > mutex_init() macro.
>
> Is the following understanding correct:
> It has 2 ways to break the "fake" circular dependencies: separate lockdep key
> for i2c_adapter vs. ec_dev.  The patch adopts the latter one because it has
> limited impact for other I2C-related drivers.

That's correct.

Re: [PATCH] platform/chromeos: cros_ec: Use per-device lockdep key

[Tzung-Bi Shih]

On Mon, Jan 09, 2023 at 03:35:08PM +0800, Chen-Yu Tsai wrote:
> On Mon, Jan 9, 2023 at 3:30 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote:
> >
> > On Mon, Jan 09, 2023 at 02:19:38PM +0800, Chen-Yu Tsai wrote:
> > > On Mon, Jan 9, 2023 at 1:46 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote:
> > > >
> > > > On Sat, Jan 07, 2023 at 01:43:57PM +0800, Chen-Yu Tsai wrote:
> > > > > On Fri, Jan 6, 2023 at 5:08 PM Tzung-Bi Shih <tzungbi@kernel.org> wrote:
> > > > > >
> > > > > > On Fri, Jan 06, 2023 at 12:55:37PM +0800, Chen-Yu Tsai wrote:
> > > > > > > Lockdep reports a bogus possible deadlock on MT8192 Chromebooks due to
> > > > > > > the following lock sequences:
> > > > > > >
> > > > > > > 1. lock(i2c_register_adapter) [1]; lock(&ec_dev->lock)
> > > > > > > 2. lock(&ec_dev->lock); lock(prepare_lock);
> > > > > > >
> > > > > > > The actual dependency chains are much longer. The shortened version
> > > > > > > looks somewhat like:
> > > > > > >
> > > > > > > 1. cros-ec-rpmsg on mtk-scp
> > > > > > >    ec_dev->lock -> prepare_lock
> > > > > > > 2. In rt5682_i2c_probe() on native I2C bus:
> > > > > > >    prepare_lock -> regmap->lock -> (possibly) i2c_adapter->bus_lock
> > > > > > > 3. In rt5682_i2c_probe() on native I2C bus:
> > > > > > >    regmap->lock -> i2c_adapter->bus_lock
> > > > > > > 4. In sbs_probe() on cros-ec-i2c (passthrough) I2C bus on cros-ec
> > > > > > >    i2c_adapter->bus_lock -> ec_dev->lock
> > > > > > >
> > > > > > > While lockdep is correct that the shared lockdep classes have a circular
> > > > > > > dependency, it is bogus because
> > > > > > >
> > > > > > >   a) 2+3 happen on a native I2C bus
> > > > > > >   b) 4 happens on the actual EC on ChromeOS devices
> > > > > > >   c) 1 happens on the SCP coprocessor on MediaTek Chromebooks that just
> > > > > > >      happen to expose a cros-ec interface, but do not have a passthrough
> > > > > > >      I2C bus
> > > > > > >
> > > > > > > In short, the "dependencies" are actually on different devices.
> > > > > >
> > > > > > Path of 4 looks weird to me.
> > > > > >
> > > > > > Could you point out where sbs_probe() gets to acquire ec_dev->lock?
> > > > >
> > > > > sbs_probe() calls sbs_get_battery_presence_and_health(), which
> > > > >
> > > > >   -> does an I2C transfer. This SBS instance is connected on the I2C bus
> > > > >      on the EC, so the I2C transfer
> > > > >
> > > > >      -> acquires i2c_adapter->bus_lock, and
> > > >
> > > > I see.
> > > >
> > > > Another question: the i2c_adapter here should be different from the native
> > > > I2C bus in 2 and 3.  Did they really form the circular dependencies?
> > >
> > > That's why it's a false positive. lockdep normally doesn't track individual
> > > instances, only classes of locks. The class is declared as part of the
> > > mutex_init() macro.
> >
> > Is the following understanding correct:
> > It has 2 ways to break the "fake" circular dependencies: separate lockdep key
> > for i2c_adapter vs. ec_dev.  The patch adopts the latter one because it has
> > limited impact for other I2C-related drivers.
> 
> That's correct.

Thanks for the explanation.  The patch looks good to me.

Just realized a kernel-doc warning after applying the patch:
$ ./scripts/kernel-doc -none include/linux/platform_data/cros_ec_proto.h
include/linux/platform_data/cros_ec_proto.h:199: warning: Function parameter
or member 'lockdep_key' not described in 'cros_ec_device'

Please fix the warning and commit title.