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

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Date:   Wed, 14 Sep 2016 14:46:01 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
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 Wed, Sep 14, 2016 at 10:26 AM, Mika Westerberg
<mika.westerberg@...ux.intel.com> wrote:
> On Tue, Sep 13, 2016 at 10:57:31PM +0200, Linus Walleij wrote:

>> 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.

To me this is just a big proof that the ACPI design-by-committee isn't
working. With Device Tree we review bindings and drivers together
and then we tend to not miss stuff like this as much.

But I realize as soon as I say that someone will pull out a counter-example
of stupid DT bindings used in the wild and make me look stupid.

>> 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.

So as far as we can determine:

(A) we are running on Braswell and
(B) we are probing this driver

we can conclude that

(C) IRQs A,B,C are reserved by BIOS?

That sounds doable?

Yours,
Linus Walleij