Re: Edit/gpiomon: Question about mode

[Kent Gibson <warthog618@gmail.com>]

On Tue, Mar 29, 2022 at 03:37:25PM +0200, Hans Kurscheidt wrote:
> 
> Am 29.03.2022 um 10:51 schrieb Kent Gibson:
> > On Tue, Mar 29, 2022 at 10:43:19AM +0200, Hans Kurscheidt wrote:
> > > Am 29.03.2022 um 10:38 schrieb Kent Gibson:
> > > > On Tue, Mar 29, 2022 at 10:07:57AM +0200, Hans Kurscheidt wrote:
> > > > > Am 29.03.2022 um 05:38 schrieb Kent Gibson:
> > > > > > On Mon, Mar 28, 2022 at 07:13:13PM +0200, Hans Kurscheidt wrote:
> > > > > > > Am 28.03.2022 um 15:16 schrieb Hans Kurscheidt:
> > > > > > > > Hi,
> > > > > > > > 
> > > > > > > > what would be the right mode for gpiomon call from
> > > > > > > > 
> > > > > > > > a shellscript executed as root from systemd at system start
> > > > > > > > 
> > > > > > > > waiting on a Pin w/ pullup for invoking shutdown upon rising* edge.
> > > > > > > > *changed
> > > > > > > > 
> > > > > > > > 
> > > > > > > > Lots of interupts, Signals and other GPIO ongoing from other user APPs &
> > > > > > > > threads in multi-user state.
> > > > > > > 2b more precise: I wired a GPIO Pin to GND.
> > > > > > > 
> > > > > > > Upon the cmd: sudo gpiomon -r -n1 <chip> <offset>
> > > > > > > 
> > > > > > > the program exits immediately with 1 event, although there was never a
> > > > > > > rising edge due to the fix wire to GND. Is this a feature or a bug, and is
> > > > > > > it reproducible?
> > > > > > > 
> > > > > > Not a feature and not reproducible for me on a Raspberry Pi4 with the
> > > > > > setup you describe, so probably a bug specific to your hardware platform,
> > > > > > whatever that may be.
> > > > > > 
> > > > > > If it is 100% reproduceable for you, and assuming it is an initialisation
> > > > > > issue so you only get the one spurious event, how about using -n2 as a
> > > > > > workaround ;-)?
> > > > > > 
> > > > > > Cheers,
> > > > > > Kent.
> > > > > It appears 2b reproduceable 100% on my OrangePi zero+ (Allwinner H5) and
> > > > > using -n2 does the trick, but isn't gpiod not supposed to work on all
> > > > > commercial HW platforms and related kernels, rather then only on RPI??
> > > > > 
> > > > gpiod will work on any platform with a supporting kernel.
> > > > How well depends on the underlying hardware and driver.
> > > > The RPi4 was merely a counter-example demonstrating that your issue is
> > > > not universal, using hardware I happen to have readily available.
> > > > 
> > > > Cheers,
> > > > Kent.
> > > So if I understand you right, gpiod works on sort of a logical level, while
> > > the HW dependend part depends of the kernel driver implementation of the
> > > specific HW?
> > > 
> > > 
> > libgpiod is a userspace library and tools to access GPIO lines via the
> > Linux GPIO character device.  The actual interfacing to the hardware is
> > performed by the kernel and appropriate drivers for your hardware.
> > As your problem does not exhibit on other hardware, the root cause
> > of your problem probably lies in the driver for your hardware, not in
> > libgpiod nor the gpiolib subsystem of the kernel.
> > 
> > But you would need to debug it further to be sure.
> > 
> > Cheers,
> > Kent.
> 
> I raised a bug report at tha Armbian forum:
> 
> https://forum.armbian.com/topic/20166-opi-zero-h5-gpiodmon-generates-spurious-interrupts-upon-invocation/
> 
> 
> I made some trial to understand if it is reproduceable, but I have
> difficulties defining, when it happens. After RESET there is no spurious
> event. The spurious event appears to happen, when the line was moved:
> 
> Could you please make another trial on your RPI w/ the following sequence:
> 
> RESET, gpiomon -r -n1 -Bpull-up <chip><line>  => No event,  -> pull line up
> /down, => event (as expected), gpiomon -r -n1 -Bpull-up <chip><line> =>
> false event
> 

Not sure what this is intending to prove, as the hardware is different,
or is that the point?

That is with the line initially pulled down externally, right?
I get an event when I disconnect the external pull-down - allowing the
internal pull-up to pull the line high and trigger the event.

I don't get the false event that you are seeing subsequently, even when
the line has been externally pulled up before being pulled down again
and gpiomon run again.

i.e. I see
 - line externally pulled down
 - power cycle RESET
 - gpiomon -r -n1 -Bpull-up <chip><line>  => No event
 - disconnect pull-down => event (RISING edge)
 - pull line up (or not - optional due to internal pull-up)
 - pull line down again
 - gpiomon -r -n1 -Bpull-up <chip><line> => No event

And I don't get continuous events if the line is left pulled up - I only
get the one.
Do you get those continuous events with out the -n1, or only when
calling gpiomon -n1 again?
Either way it looks like you've got something odd going on with the
interrupts on your hardware.

Cheers,
Kent.

> There might be an issue w/ pending interrupts, when the line is bouncing
> when pulled up/down. The 2nd gpiodmon cmd might catch one of the pending
> interrupts. (Just an idea). This would hint to an initialisation problem,
> that pending line states are not preempted, before the int is attached.