linux-kernel - Re: [PATCH v2 1/5] dt-bindings: interrupt-controller: Add Renesas RZ/A1 Interrupt Controller

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Date:   Tue, 30 Apr 2019 15:25:47 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Mark Rutland <mark.rutland@....com>,
        Simon Horman <horms@...ge.net.au>,
        Magnus Damm <magnus.damm@...il.com>,
        Chris Brandt <chris.brandt@...esas.com>,
        devicetree@...r.kernel.org,
        "open list:MEDIA DRIVERS FOR RENESAS - FCP" 
        <linux-renesas-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] dt-bindings: interrupt-controller: Add Renesas
 RZ/A1 Interrupt Controller

On Tue, Apr 30, 2019 at 10:34 AM Marc Zyngier <marc.zyngier@....com> wrote:
>
> On 30/04/2019 16:02, Rob Herring wrote:
> > On Tue, Apr 30, 2019 at 7:13 AM Geert Uytterhoeven
> > <geert+renesas@...der.be> wrote:
> >>
> >> Add DT bindings for the Renesas RZ/A1 Interrupt Controller.
> >>
> >> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> >> ---
> >> v2:
> >>   - Add "renesas,gic-spi-base",
> >>   - Document RZ/A2M.
> >> ---
> >>  .../renesas,rza1-irqc.txt                     | 30 +++++++++++++++++++
> >>  1 file changed, 30 insertions(+)
> >>  create mode 100644 Documentation/devicetree/bindings/interrupt-controller/renesas,rza1-irqc.txt
> >>
> >> diff --git a/Documentation/devicetree/bindings/interrupt-controller/renesas,rza1-irqc.txt b/Documentation/devicetree/bindings/interrupt-controller/renesas,rza1-irqc.txt
> >> new file mode 100644
> >> index 0000000000000000..ea8ddb6955338ccd
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/interrupt-controller/renesas,rza1-irqc.txt
> >> @@ -0,0 +1,30 @@
> >> +DT bindings for the Renesas RZ/A1 Interrupt Controller
> >> +
> >> +The RZ/A1 Interrupt Controller is a front-end for the GIC found on Renesas
> >> +RZ/A1 and RZ/A2 SoCs:
> >> +  - IRQ sense select for 8 external interrupts, 1:1-mapped to 8 GIC SPI
> >> +    interrupts,
> >> +  - NMI edge select.
> >> +
> >> +Required properties:
> >> +  - compatible: Must be "renesas,<soctype>-irqc", and "renesas,rza1-irqc" as
> >> +               fallback.
> >> +               Examples with soctypes are:
> >> +                 - "renesas,r7s72100-irqc" (RZ/A1H)
> >> +                 - "renesas,r7s9210-irqc" (RZ/A2M)
> >> +  - #interrupt-cells: Must be 2 (an interrupt index and flags, as defined
> >> +                                in interrupts.txt in this directory)
> >> +  - interrupt-controller: Marks the device as an interrupt controller
> >> +  - reg: Base address and length of the memory resource used by the interrupt
> >> +         controller
> >> +  - renesas,gic-spi-base: Lowest GIC SPI interrupt number this block maps to.
> >
> > Why isn't this just an 'interrupts' property?
>
> That's likely because of kernel limitations. The DT code does an
> of_populate() on any device that it finds, parse the "interrupts"
> propertiy, resulting in the irq_descs being populated.
>
> That creates havoc, as these interrupts are not for this device, but for
> something that is connected to it. This is merely a bridge of some sort.

'interrupt-map' would avoid that problem I think.

> Furthermore, this is a rather long established practice: gic-v2m,
> gic-v3-mbi, mediatek,sysirq, mediatek,cirq... All the bits of glue that
> for one reason or another plug onto the GIC use the same method.

All handling the mapping to the parent in their own way...

> > Plus, without 'interrupts' walking the hierarchy is broken.
>
> Erm... Which hierarchy?

of_irq_init() expects that an interrupt-controller without an
interrupt-parent is the root controller. So you're right. We only need
to have an 'interrupt-parent', but not 'interrupts'.

Rob