[Letux-kernel] [PATCH 0/6] bq2429x: Clean up driver for future fixes

Nick Elsmore nicholaselsmore at gmail.com
Thu Aug 13 17:51:25 CEST 2020

Hi Nikolaus,

> * Interrupts/poll events are often missed, possibly due to hangups in the
> work queue.
> I haven't observed this in my tests. Do you have a specific example? Or a
> theory when and why it can happen?
I instrumented the driver to print before var_lock was acquired (I left
loglevel below debug, because currently there are lots of debug prints
which flood the output and make it difficult to filter out whats
important).  I noticed that I would often not see bq2429x_usb_detect
executing until a number of seconds or minutes after I plugged or unplugged
the USB OTG.  If I plugged or unplugged multiple times, I would eventually
get all of the calls occurring at once after the delay.  This leads me to
believe that the workqueue is hanging somewhere.

Interestingly, I would sometimes see no new interrupts for this device
triggered in /proc/interrupts.  This contradicts the theory that the issue
is a hangup in the workqueue, but it could be a combination of both issues
in the workqueue and IRQ handler.

> > * Plug/unplug events are not properly detected, due to either work queue
> hangups as described above or faulty logic determining plug status
> Yes, plug/unplug detection is quite some guesswork. A better strategy
> would be to connect to the USB-PHY...
I do not see why we would need to connect to the USB-PHY.  Interrupts from
the bq2429x should be sufficient to determine whether or not the bq2429x is
connected to VBUS and whether or not the bq2429x has determined this to be
a good power source and is using it.  I have patches which implement the
correct logic for handling this in my queue.

> > * Watchdog is left on (if not disabled by bootloader) and not serviced.
> It should be disabled by bootloader and kept in disabled state by the
> driver.
> Contrary to what we all would suspect it is not a safety watchdog which
> would e.g. cut processor power or charging after a kernel panic or stall.
> It just a mechanism to auto-reset the bq2429x registers to default values
> which could also be done through writing all registers.
> So I do not see how to use it for practical purposes.
Yes.  We should not assume, however, that the bootloader has disabled the
watchdog.  We should make sure its disabled.

> > This is not properly handled.
> > * The following properties are missing:
> I am not sure if the charger can report a reasonable value for health.
We'll see.  I have patches in my queue that determine reasonable values for
health, but we will see how they fare in review.

> Generally I find the patches good from a cursory glance, but I have to do
> a life check since it is not easy to see from the git diffs, what is
> changed (any why) and if all functions are transformed correctly. This
> takes at least until next week.
Yep, while these patches don't (shouldn't) modify any of the logic, they
are rather large and introduce a good amount of restructuring.  I have
submitted these patches first before integrating any logic modifications as
its possible they have introduced regression.  From my tests, the behavior
seems the same with and without the patches.

Nick Elsmore
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