linux-kernel - Re: [RFC PATCH v1 3/4] dt-bindings: interrupt-controller: realtek,rtl-intc: replace irq mapping

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Message-ID: <87v8zaz7ml.wl-maz@kernel.org>
Date:   Mon, 27 Dec 2021 10:04:18 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Sander Vanheule <sander@...nheule.net>
Cc:     Thomas Gleixner <tglx@...utronix.de>, devicetree@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>,
        Birger Koblitz <mail@...ger-koblitz.de>,
        Bert Vermeulen <bert@...t.com>,
        John Crispin <john@...ozen.org>, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 3/4] dt-bindings: interrupt-controller: realtek,rtl-intc: replace irq mapping

On Thu, 23 Dec 2021 19:29:23 +0000,
Sander Vanheule <sander@...nheule.net> wrote:
> 
> On Thu, 2021-12-23 at 18:00 +0000, Marc Zyngier wrote:
> > On Thu, 23 Dec 2021 12:08:33 +0000,
> > Sander Vanheule <sander@...nheule.net> wrote:
> > > 
> > > The binding incorrectly specified the "interrupt-map" property should be
> > > used, although the use is non-standard. A quirk had to be introduced in
> > > commit de4adddcbcc2 ("of/irq: Add a quirk for controllers with their own
> > > definition of interrupt-map") to allow the driver to function again.
> > 
> > That's too late. We have released a kernel with this binding, and it
> > will live on forever until we totally remove the platform from the
> > tree.
> > 
> > DT is an ABI, and only time travel can fix this blunder.
> 
> Taking into account your comments on the previous patch, this change
> wouldn't even be required if I correct the mappings for my
> devices. But that wouldn't get rid of the assumed mapping between
> output lines and parent interrupts.

A driver can always ignore some information from the DT and do its own
thing. No sure if that addresses your problem though.

> 
> To what extent can the binding be updated to get rid of this
> assumption? Or would that require a completely new binding?

You can only extend a binding in a two-way fashion: old kernel works
with new DT, new kernel works old DT. Which means that in practice,
you can only *add* information to the DT, and have reasonable defaults
in the driver when you don't find it.

	M.

-- 
Without deviation from the norm, progress is not possible.