On 18-02-17 19:09, James Maki wrote:
Hi Eric,
I have an TI am335x that is using a i2c PMIC with pm_power_off hook
which locks up on shutdown. The pm_power_off hook gets stuck obtaining
i2c_lock_adapter(). The holder of the lock is the lis3lv02d
accelerometer which never releases it.
I do not think there is an issue in lis3lv02d. I think this is a general
issue with i2c since other drivers have the same design. What I don't
have is clear understanding of if/when/how i2c_transfer() can be called
post kernel_power_off(). Is it possible to call i2c_transfer() at this
point. I have tried calling schedule() and msleep() inside of
kernel_power_off() after syscore_shutdown(). It looks like interrupts
are enabled and I can still schedule at this point. So how is it
possible that lis3lv02d is never able to exit the i2c_transfer()? Is
there some other lock inside i2c_transfer that it is blocking on?
Is it possible that the process which had the accelerometer open has
exited while holding the i2c lock. Is it even possible for a device to
shutdown or file to close while holding a lock in the kernel?
I looked at adding a lis3lv02d_i2c_shutdown, but that was too late in
the process already and the lis3lv02d was already stuck. Is there a very
early place during shutdown that I can kick everyone off the i2c bus?
Obviously this might not be the best general solution, but my concern
right now is fixing the problem on this particular system first.
Dear James,
Unfortunately, I don't know enough about I2C to be able to help you.
Honestly, I know pretty much nothing about this subsystem, and all the
code dealing with it in the lis3lv02d driver has been contributed by
other people.
The only thing I can say is that indeed it does sound more like an issue
happening at the I2C level than in this specific driver. Concerning the
lock, if I understand correctly, it shouldn't possible for a process
talking to the accelerometer to suddenly be killed, while a kernel lock
is held, preventing it to ever be release. That said, in practice, there
are sufficiently enough bugs in the kernel for this to be possible ;-)
So I'd suggest you to contact people who understand well the I2C
subsystem. I've CC'd Wolfram, maintainer of the subsystem, and the
dedicated mailing-list.
Best,
Éric
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