linux-kernel - Re: [PATCH v3] pinctrl: ocelot: Fix interrupt controller

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Date:   Tue, 20 Sep 2022 14:34:09 +0200
From:   Michael Walle <michael@...le.cc>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     horatiu.vultur@...rochip.com, UNGLinuxDriver@...rochip.com,
        andy.shevchenko@...il.com, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] pinctrl: ocelot: Fix interrupt controller

Am 2022-09-20 14:28, schrieb Linus Walleij:
> On Tue, Sep 20, 2022 at 2:06 PM Michael Walle <michael@...le.cc> 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