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Subject: Re: [PATCH v5 05/10] dt-bindings: irqchip: Introduce TISCI Interrupt
 router bindings
To:     Tony Lindgren <tony@atomide.com>
CC:     Nishanth Menon <nm@ti.com>,
        Device Tree Mailing List <devicetree@vger.kernel.org>,
        <jason@lakedaemon.net>, Peter Ujfalusi <peter.ujfalusi@ti.com>,
        <marc.zyngier@arm.com>, Sekhar Nori <nsekhar@ti.com>,
        <linux-kernel@vger.kernel.org>, Tero Kristo <t-kristo@ti.com>,
        Rob Herring <robh+dt@kernel.org>,
        Santosh Shilimkar <ssantosh@kernel.org>, <tglx@linutronix.de>,
        Linux ARM Mailing List <linux-arm-kernel@lists.infradead.org>,
        Linus Walleij <linus.walleij@linaro.org>
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From:   Lokesh Vutla <lokeshvutla@ti.com>
Message-ID: <ffc39399-a6bc-aabf-b701-d419346f9a71@ti.com>
Date:   Wed, 20 Feb 2019 22:47:37 +0530
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Hi Tony,

On 2/20/2019 10:06 PM, Tony Lindgren wrote:
> Hi,
> 
> Some more info on chained irq vs mux below that might
> help.
> 
> * Tony Lindgren <tony@atomide.com> [190219 15:36]:
>> * Lokesh Vutla <lokeshvutla@ti.com> [190219 08:51]:
>>> With this can you tell me how can we not have a device-tree and still support
>>> irq allocation?
>>
>> Using standard dts reg property to differentiate the interrupt
>> router instances. And if the interrupt router is a mux, you should
>> treat it as a mux rather than a chained interrupt controller.
>>
>> We do have drivers/mux nowadays, not sure if it helps in this case
>> as at least timer interrupts need to be configured very early.
> 
> Adding Linus Walleij to Cc since he posted a good test to
> consider if something should use chained (or nested) irq:
> 
> "individual masking and ACKing bits and can all be used at the
>  same time" [0]

Interrupt Router just routes M inputs to N outputs. One input can only
be mapped to one output. This is a clear case of a hierarchical domain
and the driver is implementing it.

Thanks and regards,
Lokesh

> 
> Not sure if we have that documented somewhere?
> 
> But seems like the interrupt router should be set up as
> a separate mux driver talking with firmware that the
> interrupt controller driver calls on request_irq(>
> Cheers,
> 
> Tony
> 
> 
> [0] https://marc.info/?l=linux-omap&m=155065629529311&w=2
>