Kernel Module Load Order

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1

I’m cleaning up our kernel modules by adding the required kernel modules to my MDEF files the same as Mangoh The mangOH repository now uses a Legato 18.05.1 feature

I changed the order my kernel modules load (specifically the BMI160 and IIO) to match the Mango Red .mdef file and then they won’t load. I change the order back and then it works.

Old way that works in SDEF
// BMI160 accelerometer, NOTE: Order id important here
$PROJ_ROOT/drivers/bmi160/bmi160
$PROJ_ROOT/drivers/bmi160/bmi160-i2c

// battery charger
$PROJ_ROOT/drivers/bq24296/bq24296

// Required for BMI160 NOTE: Order is important here
$PROJ_ROOT/drivers/iio/iio
$PROJ_ROOT/drivers/iio/iio-kfifo-buf
$PROJ_ROOT/drivers/iio/iio-triggered-buffer

Mangoh Red way that doesn’t work in SDEF
// BMI160 accelerometer, NOTE: Order id important here
$PROJ_ROOT/drivers/bmi160/bmi160-i2c
$PROJ_ROOT/drivers/bmi160/bmi160

// battery charger
$BRNKL_ROOT/drivers/bq24296/bq24296

// Required for BMI160 NOTE: Order is important here
$BRNKL_ROOT/drivers/iio/iio-triggered-buffer
$BRNKL_ROOT/drivers/iio/iio-kfifo-buf
$BRNKL_ROOT/drivers/iio/iio

Thoughts? Is there something I’m missing with the new method. I’m running Legato 18.09.0 on a WP85.

2

Take a look at dmesg and logread output and see if there are any clues in there about why the modules are failing to load.

3

@dfrey I’m not seeing a lot of my print states in dmesg or the log. How do I enabled the DEBUG level messages in the kernel modules?

4

https://elinux.org/Debugging_by_printing#Log_Levels

5

@dfrey Thanks I looked at that resource and it wasn’t much help. I have several of these dev_dbg statements but I don’t seem them in the dmesg or logread

I am basically recreating what you did here https://github.com/mangOH/mangOH/commit/fd1399c48c7924930bace8334071c589ec3c26ec moving from the number files to the requires statements but it’s not working.

Any additional help would be greatly appreciated, thanks.

6

The quick and dirty method is to raise the log level of the messages so that they do appear. I too have had issues with “debug” level messages and never really got to the bottom of it.

7

So what’s the difference between dev_info and printk? Any thoughts on my comments about moving away from the number based kernel module loading to the requires statements?

8

Hi, dev macros call into printk with the different levels as @dfrey mentioned.
They are the recommended way of printing log messages in device drivers
these days, just like pr_ are in many kernel subsystems. I think you may not be
seeing messages as if you look at your Kernel config it probably has this set:
CONFIG_DYNAMIC_DEBUG=y
This means you have to turn on you device debug messages on the target at
run-time on the fly as explained here:
https://www.kernel.org/doc/html/v5.1/admin-guide/dynamic-debug-howto.html
There are also other reasons dev_dbg doesn’t print. Please see the kernel.org
docs for more details.

I’m unsure about the Legato module loading ordering issues, I’ll let @dfrey
pipe in on those once you get the log messages.