Re: /dev/gpiochipX event filtering throws away wanted events

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Sun, Aug 19, 2018 at 7:22 PM Bartosz Golaszewski <brgl@xxxxxxxx> wrote:

> While your concern is real I think that our approach is mostly fine -
> we try to read the value as soon as we can in the interrupt handler.
>
> What we could do however for some theoretical improvement is use
> gpiod_get_value() since we're in non-sleeping context and maybe even
> call it as the very first operation - even before calling
> ktime_get_real_ns().

We can call *get_value() directly in the hard interrupt handler
lineevent_irq_handler() if and only if the IRQ handler does not
sleep, such as MMIO GPIO, but not on I2C expanders for example.

The code is written to deal with any cases and assuming the
worst so right now it is just timestamping in the hop half.

But we could check if .can_sleep() is set on the struct gpio_chip
and if it isn't, just read the value directly in the hardirq handler.

Yours,
Linus Walleij