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

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Date:	Mon, 13 Jun 2016 16:57:41 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Mason <slash.tmp@...e.fr>,
	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>,
	Sebastian Frias <sf84@...oste.net>
Cc:	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 13/06/16 16:49, Mason wrote:
> 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.

Up to 224 SPIs actually, plus 16 PPIs.

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