If an I2C GPIO multiplexer is driven by a GPIO provided by an expander
when there's a second expander using the same device driver on one of
the I2C bus segments, lockdep prints a deadlock warning when trying to
set the direction or the value of the GPIOs provided by the second
expander.
This series exports an already existing function from i2c-core as
public API and reuses it in pca953x to pass a correct lock subclass
to lockdep.
Note: if this series gets merged, I'll prepare follow-up patches for
other expanders for which a similar problem could potentially occur.
Tested with the following setup:
------- --------- Bus segment 1 | |
| | | |--------------- Devices
| | SCL/SDA | | | |
| Linux |-----------| I2C MUX | - - - - -
| | | | | Bus segment 2
| | | | |-------------------
------- | --------- |
| | - - - - -
------------ | MUX GPIO | |
| | | Devices
| GPIO | | | |
| Expander 1 |---- - - - - -
| | |
------------ | SCL/SDA
|
------------
| |
| GPIO |
| Expander 2 |
| |
------------
where expander 1 is a pca9534 and expander 2 is a pca9535.
v1 -> v2:
- added patches 1/4, 2/4 & 3/4
- used i2c_adapter_depth() in patch 4/4 in order to detect multiple
adapter nesting
Bartosz Golaszewski (4):
i2c: export i2c_adapter_depth()
lockdep: make MAX_LOCKDEP_SUBCLASSES unconditionally visible
i2c: add a warning to i2c_adapter_depth()
gpio: pca953x: fix an incorrect lockdep warning
drivers/gpio/gpio-pca953x.c | 2 ++
drivers/i2c/i2c-core.c | 12 +++++-------
include/linux/i2c.h | 1 +
include/linux/lockdep.h | 4 ++--
4 files changed, 10 insertions(+), 9 deletions(-)
--
2.7.4
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