Re: [PATCH v3] pinctrl: ocelot: Fix interrupt controller

[Michael Walle]

Am 2022-09-20 14:28, schrieb Linus Walleij:
> On Tue, Sep 20, 2022 at 2:06 PM Michael Walle <michael@xxxxxxxx> wrote:
>
> > Our board has a shared active low interrupt line, connected to a quad 
> > PHY
> > LAN8814 and two GPY215 PHYs. I've gave this a try but it doesn't seem 
> > to
> > work. It seems the interrupt fires multiple times. If I plug a cable 
> > in
> > one of the LAN8814 ports, I see that the interrupt count in
> > /proc/interrupts has increased by two. If I use a GPY215 port, I see 
> > about
> > 40 interrupts firing.
>
> A lot of interrupts firing is very typical for level IRQs.

Common but wrong? Except in the error case, /proc/interrupts
was always reliable on our boards :)

> So I assume these are wire-OR, i.e. exploiting open drain with
> a pull-up resistor.

Yes, the usual shared line interrupts.

> Just checking: since these drivers obviously must pass pass
> IRQF_SHARED, have you also made sure that each driver also
> will properly return IRQ_HANDLED if the interrupt was for them
> (triggered by "their" hardware) but IRQ_NONE if the interrupt was
> not for them (triggered by something else)?

Thanks, I'll check it.

> The IRQ core relies on all drivers to do the right thing here.
>
> Otherwise the IRQ will just re-fire until someone/something
> manages to properly handle it and drive the line high again.
>
> A typical case would be the LAN8814 driver having been probed
> first, thus its IRQ handler will be visited first, and always returning
> IRQ_HANDLED thereby "stealing" the irq from everyone else.
>
> Another possible problem is if you don't have an external pull-up
> resistor and you need some pin config to enable pull-up on the
> SoC input line. This will generate a lot of IRQs.

I've checked with a scope, the levels and edges look good.

> A third problem would be that the line need time to rise.
> But that should be uncommon.

I haven't looked at the code of this patch, but obiously it
is emulating the level triggered behavior with just a pin change
interrupt. There might also be something wrong there, too.

-michael