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

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Message-ID: <29e95406-b9fb-fbb6-9240-c3914d885e88@arm.com>
Date:   Tue, 30 Apr 2019 16:34:55 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Rob Herring <robh+dt@...nel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     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 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.

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.

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

Erm... Which hierarchy?

Thanks,
	
	M.
-- 
Jazz is not dead. It just smells funny...