From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754967AbcGFNuS (ORCPT ); Wed, 6 Jul 2016 09:50:18 -0400 Received: from foss.arm.com ([217.140.101.70]:58309 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754040AbcGFNuQ (ORCPT ); Wed, 6 Jul 2016 09:50:16 -0400 Subject: Re: [RFC PATCH v1] irqchip: add support for SMP irq router To: Sebastian Frias , Jason Cooper References: <577542D1.4070307@laposte.net> <577A5260.3070001@free.fr> <577BA854.6090503@laposte.net> <20160705144151.GE3348@io.lakedaemon.net> <577BCFD2.8060203@laposte.net> <20160705155306.GG3348@io.lakedaemon.net> <577BE288.70200@laposte.net> <577BE4D8.2040601@arm.com> <577BE75B.4070109@laposte.net> <577BEABE.2010204@arm.com> <577CE1DE.6080502@laposte.net> Cc: Mason , LKML , Thomas Gleixner From: Marc Zyngier X-Enigmail-Draft-Status: N1110 Organization: ARM Ltd Message-ID: <577D0C95.2000703@arm.com> Date: Wed, 6 Jul 2016 14:50:13 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Icedove/38.7.0 MIME-Version: 1.0 In-Reply-To: <577CE1DE.6080502@laposte.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/07/16 11:47, Sebastian Frias wrote: >>> I think I'm missing something, what is the difference between the domains >>> described by nodes in the DT for irq-tango.c (arch/arm/boot/dts/tango4-common.dtsi) >>> and the DT from my RFC? >> >> The fundamental difference is that with your new fancy controller, you >> can decide what is going where, while the previous one is completely set >> in stone (the output line is a direct function of the input line). > > I think that's where part the misunderstanding comes from. > IMHO the output line is not a direct function of the input line. > Any of the 64 IRQ lines entering the "old controller" (irq-tango.c) can be > routed to any of its 3 outputs. Then the current DT binding isn't properly describing the HW. > The only thing fixed is which GIC input is connected to those 3 outputs, ie: > GIC inputs 2, 3 and 4. > > In the the "new controller" (irq-tango_v2.c, this RFC), any of 128 IRQ lines > can be routed to any of 24 outputs, connected to GIC inputs 0...23. > > In a nutshell: > - "old controller": routes [0...N] => GIC inputs [2...4] > - "new controller": routes [0...M] => GIC inputs [0...23] > > So, when we think about it, if the "new DT" specified 24 domains, it would > be equivalent of the "old DT" with 3 domains, right? Indeed, but I consider the "old" binding to be rather misleading. It should have been described as a router too, rather than hardcoding things in DT. Granted, it doesn't matter much when you only have 3 possible output lines. But with 24 outputs, that becomes much more relevant. > > That's why it seemed more or less natural to keep describing the domains in > the DT, the main reason for that being that it allowed the user to specify > the IRQ sharing in the DT, and this is precisely the key point of this. > > So, putting aside routing considerations and the discussion above, I think > a simpler question is: if the domains should not be described in the DT, > how can we define the IRQ sharing in the DT? You could have a set of sub-nodes saying something like this: mux-hint0 { inputs = <1 45 127>; } mux-hint1 { inputs = <2 33>; } (or maybe you can have that as direct properties, but you get the idea). Here, you have two output pins dedicated to muxed interrupts (assuming they are all level interrupts), and the last 22 can be freely allocated as direct routes. Thanks, M. -- Jazz is not dead. It just smells funny...