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Subject: Re: [PATCH v2 09/10] irqchip: ti-sci-inta: Add support for Interrupt
 Aggregator driver
To:     Marc Zyngier <marc.zyngier@arm.com>
CC:     Lokesh Vutla <lokeshvutla@ti.com>, Nishanth Menon <nm@ti.com>,
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From:   Peter Ujfalusi <peter.ujfalusi@ti.com>
Message-ID: <f7b6d570-a8f4-6f8b-7995-eac69fef8fa1@ti.com>
Date:   Thu, 1 Nov 2018 11:14:15 +0200
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Hi Marc,

On 11/1/18 11:00 AM, Marc Zyngier wrote:
> On Thu, 01 Nov 2018 07:55:12 +0000,
> Peter Ujfalusi <peter.ujfalusi@ti.com> wrote:
>>
>> Lokesh,
>>
>> On 10/29/18 3:04 PM, Lokesh Vutla wrote:
>>>>> With the above information, linux should send a message to
>>>>> system-controller using TISCI protocol. After policing the given
>>>>> information, system-controller does the following:
>>>>> - Attaches the interrupt(INTA input) to the device resource index
>>>>> - Muxes the interrupt(INTA input) to corresponding vint(INTA output)
>>>>> - Muxes the vint(INTR input) to GIC irq(INTR output).
>>>>
>>>> Isn't there a 1:1 mapping between *used* INTR inputs and outputs?
>>>> Since INTR is a router, there is no real muxing. I assume that the
>>>> third point above is just a copy-paste error.
>>>
>>> Right, my bad. INTR is just a router and no read muxing.
>>
>> INTR can mux M interrupt inputs to N interrupt outputs.
>> One selects which interrupt input is outputted on the given interrupt
>> output.
>> It is perfectly valid (but not sane) to select the same interrupt input
>> to be routed to _all_ interrupt output for example.
>>
>> Not sure if we are going to use this for anything but 1:1 mapping, but
>> might worth keeping in mind...
> 
> It's not obvious how you'd use this "feature". Interrupt replicator,
> should one of the output be tied to another part of the system? Or
> maybe that's just the result of reusing some generic block...

I think the intention is that different virtualized OS would got
assigned with different range of NAVSS GIC irqs and there might be a
case when more than one virtualized environment need to get a GIC irq
for the same virt. Timer interrupts comes to mind first, but there could
be other cases when the same virt should trigger on multiple GIC line.

- Peter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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