linux-kernel - Re: [PATCH] pinctrl: cherryview: Do not mask all interrupts on probe

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Date:   Wed, 14 Sep 2016 11:26:10 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Phidias Chiang <phidias.chiang@...onical.com>,
        Anisse Astier <anisse@...ier.eu>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Yu C Chen <yu.c.chen@...el.com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pinctrl: cherryview: Do not mask all interrupts on probe

On Tue, Sep 13, 2016 at 10:57:31PM +0200, Linus Walleij wrote:
> On Tue, Sep 13, 2016 at 2:52 PM, Mika Westerberg
> <mika.westerberg@...ux.intel.com> wrote:
> > [Me]
> >> A-ha! But why are you registering a irqdomain entry for an interrupt
> >> that cannot be used, hm?
> >
> > Unfortunately there is no way to figure out from the hardware (or
> > firmware) whether the interrupt is supposed to be used by the GPIO
> > driver or something else.
> 
> So the fact that we kept it in valid-mask in the DT was a hint: it is
> part of the hardware description.
> 
> Isn't this (a list of what IRQs are reserved by BIOS) by sheer logic
> something that ACPI should provide?
> 
> Or is this one of those "well we could alter ACPI tables but we can't
> because they already shipped so we just can't so now we need to
> hack around it"?

Isn't it always the case? ;-)

Once the hardware enters stores the firmware cannot be changed anymore
and we get all the fun working around problems in the OS.

> Letting Linux map an interrupt it cannot access and then papering it
> over by using handle_simple_irq() just feels wrong to me.
> 
> I would argue for associating the mask of BIOS-reserved IRQs with
> something in ACPI and implement the mentioned scheme to avoid
> even mapping them seems most logical.

I'm going to re-read the hardware spec and see if there is anything we
can do about this. The newer hardware (Skylake, Broxton) has a bit that
tells the IRQ is routed directly to I/O-APIC but unfortunately Braswell
misses that. There may be something else, though.

> If we have to use handle_simple_irq() by default on all I prefer to put
> in a very fat comment of the type:
> 
> /*
>  * HACK HACK HACK HACK HACK HACK HACK HACK HACK HACK
>  *
>  * Some interrupts are BIOS-reserved but we don't know which ones!
>  * So we anyway map them and assign the handle_simple_irq() handle
>  * to them, leaving them unmasked, pretending they can be used, and
>  * pray no-one will accidentally use these GPIO IRQs.
>  *
>  * HACK HACK HACK HACK HACK HACK HACK HACK HACK HACK
>   */

OK, got it.

Let me try to come up with a solution that both works and does not
involve using handle_simple_irq.