linux-kernel - Re: Using irq-crossbar.c

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Date:	Mon, 13 Jun 2016 17:49:55 +0200
From:	Mason <slash.tmp@...e.fr>
To:	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>,
	Sebastian Frias <sf84@...oste.net>
Cc:	Marc Zyngier <marc.zyngier@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Mans Rullgard <mans@...sr.com>
Subject: Re: Using irq-crossbar.c

On 13/06/2016 17:42, Lennart Sorensen wrote:
> On Mon, Jun 13, 2016 at 04:57:13PM +0200, Sebastian Frias wrote:
>> Actually we have 128 inputs and 24 outputs, the 24 outputs go straight to the GIC.
>> The HW block is a many-to-many router.
>> There are 128 32bit registers which specify, for each of the corresponding 128 inputs, to which of the 24 outputs it would be routed to.
>>
>> There are 4 32bit registers that can show the RAW status of the 128 inputs, but they do not latch on the inputs.
>> That's why our understanding is that on Linux terms it is not an interrupt controller, but just a many-to-many mux, the only real interrupt-controller (where one can set if the line is active high or low for example) is the GIC.
> 
> Well that does just sound like a mux.  But that does mean you either
> can't use more than 24 inputs at once, or you will be sharing interrupts.
> 
> I really hate shared interrupts so I would never design something that
> way, but it is simpler.

If I am not mistaken, the Cortex A9 MPCore GIC has 32 inputs.

So any SoC with more than 32 devices capable of generating IRQs
would have to share interrupts, right?

Regards.