linux-kernel - Re: [PATCH v5 05/10] dt-bindings: irqchip: Introduce TISCI Interrupt router bindings

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Date:   Sat, 16 Feb 2019 08:59:55 +0530
From:   Lokesh Vutla <lokeshvutla@...com>
To:     Tony Lindgren <tony@...mide.com>
CC:     <marc.zyngier@....com>, Nishanth Menon <nm@...com>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, <tglx@...utronix.de>,
        <jason@...edaemon.net>,
        Linux ARM Mailing List <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        Device Tree Mailing List <devicetree@...r.kernel.org>,
        Sekhar Nori <nsekhar@...com>, Tero Kristo <t-kristo@...com>,
        Peter Ujfalusi <peter.ujfalusi@...com>
Subject: Re: [PATCH v5 05/10] dt-bindings: irqchip: Introduce TISCI Interrupt
 router bindings

Hi Tony,

On 2/15/2019 9:46 PM, Tony Lindgren wrote:
> Hi,
> 
> * Lokesh Vutla <lokeshvutla@...com> [190214 18:03]:
>> On 2/14/2019 11:16 PM, Tony Lindgren wrote:
>>> But I'd rather have a proper hardware based phandle + index
>>> type mapping in the dts if possible though.
>>
>> The idea about sysfw here is that Linux is not aware of anything about
>> this device(Interrupt Router). It cannot even access any of its
>> registers. As a user Linux should know who is the parent to which the
>> Interrut router output should be configured. Then query sysfw about the
>> range of gic irqs allocated to it. Now for configuration, Linux should
>> pass the the input to interrupt router, gic irq no, and gic id(by which
>> sysfw uniquely identifies GIC interrupt controller with the SoC).  Based
>> on these parameters Interrupt Router registers gets configured.
> 
> If the interrupt router hardawre is hidden away from Linux,
> just leave it out of the device tree completely and have the
> interrupt controller driver request the routing.

Yes while requesting you should at-least specify which is your
destination interrupt-controller Else how does the sysfw even know to
whom the requester wants the routing to happen to. You do know that we
are dealing with a heterogeneous system where there are more the one
destination interrupt controllers(GIC, R5 VIM  etc etc..). This is what
the DT property is specifying and we cannot query a device based on a name.

> 
> The dts node for the interrupt controller should describe a
> proper Linux device, that is with reg entries and so on.

You are asking to just keep the compatible property :)

I am no where denying that. But the cases where the firmware does the
configuration DT spec[1] clearly mentions about the interface.

Please take a look at arm-psci devicetree binding documentation where
the function ids are represented using which each psci function is invoked.

[1]
https://github.com/devicetree-org/devicetree-specification/releases/download/v0.2/devicetree-specification-v0.2.pdf

Thanks and regards,
Lokesh