Re: [libgpiod] gpiomon loses events

[Andy Shevchenko <andy.shevchenko@xxxxxxxxx>]

On Thu, Sep 17, 2020 at 1:37 PM Maxim Devaev <mdevaev@xxxxxxxxx> wrote:

> > I already applied the patch to the master branch and backported it to
> > v1.5.x[1]. Please give it a try. I will make a bugfix release soon
> > too.
>
> Everything seems to be working fine now. In any case, I plan to use
> event_read_multiple (), just for reasons of paranoia (and for older
> versions) :)
>
> > If you are losing events then this is what you will get.
> > No attempt is made in the kernel or libgpiod to keep rising and falling
> > events paired (until debounce support in GPIO CDEV uAPI v2 arrives).
>
> Okay, thanks. I will take this into account.
>
> > What is your use case?  Are you seeing these problems in practice or
> > only because you are generating events faster than you service them
> > for testing?
>
> I make an IP-KVM and use GPIO to read the status of the HDD led on the
> managed server's motherboard. This led operates in PWM mode, and if
> the frequency is high enough and then the activity is stopped, then
> there is a chance that the actual state of the led will be 0, while
> the last state received from the library will be 1.

As a workaround can you simply read the state separately (yes, I
understand that is not ideal but may help a bit to mitigate the
current situation)?
I.o.w. if you haven't got a new event during certain period of time,
read the pin state to actualise it.


-- 
With Best Regards,
Andy Shevchenko