Re: Sv: GPIO level IRQ fires twice each time.

[Kent Gibson <warthog618@gmail.com>]

On Mon, Jan 24, 2022 at 07:12:31AM +0000, Markus Mirevik wrote:
> > On Fri, Jan 21, 2022 at 09:03:43AM +0000, Markus Mirevik wrote:
> > > I have a problem with a custom bord based on SoC am335x and a driver
> > utilizing a GPIO line for interrupts.
> > >
> > > I have two mcp2518fd chip connected on one SPI line and everything
> > works, but it's hogs a lot of CPU.
> > > In the current setup only one chip is connected and it only receives packets.
> > >
> > > The mcp2518fd is connected with 2 interrupt lines one "main" and one for
> > rx frames.
> > >
> > > The problem is that for every frame received the interrupt handler is run
> > twice, which is kind of expensive since it's a SPI call to the chip to check
> > interrupt registers.
> > >
> > > To me it looks like the interrupt is fired again as soon as it's unmasked.
> > Either because it's queued? or maybe not cleared internally?
> > > I have scoped the interrupt signal and its real good without any glitches.
> > >
> > > I'm currently running a yocto build:
> > > Linux botekcc 5.10.79-yocto-tiny #1 SMP Tue Nov 16 03:57:43 UTC 2021
> > > armv7l armv7l armv7l GNU/Linux
> > >
> > > But the mcp251xfd driver is from net-next/master
> > >
> > > mcp251xfd_irq is the irqhandler for the mcp2518fd and is added like this:
> > > err = request_threaded_irq(spi->irq, NULL, mcp251xfd_irq,
> > >                                    IRQF_SHARED | IRQF_ONESHOT,
> > >                                    dev_name(&spi->dev), priv);
> > >
> > 
> > You haven't set a IRQF_TRIGGER flag, so you are getting the "as-already-
> > configured" behaviour, which on your setup is both edges?
> > Try adding IRQF_TRIGGER_RISING, IRQF_TRIGGER_FALLING,
> > IRQF_TRIGGER_HIGH or IRQF_TRIGGER_LOW, as appropriate to your use
> > case, to your flags.
> > 
> > Cheers,
> > Kent.
> 
> I have tried with the IRQF_TRIGGGER_LOW flag as well. With same result. i.e the interrupt is fired again as soon as the handler is ready. Even if the interrupt line is deactivated. 
> However if I change the trigger to edge falling the interrupt will only fire once. But his will inevitably lead to a missed edge eventually.
> 

 Why is a missed edge inevitable?

Cheers,
Kent.