From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753654AbcGFKsI (ORCPT ); Wed, 6 Jul 2016 06:48:08 -0400 Received: from smtpoutz298.laposte.net ([178.22.154.198]:35594 "EHLO smtp.laposte.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750937AbcGFKsG (ORCPT ); Wed, 6 Jul 2016 06:48:06 -0400 Subject: Re: [RFC PATCH v1] irqchip: add support for SMP irq router To: Marc Zyngier , 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> Cc: Mason , LKML , Thomas Gleixner From: Sebastian Frias Message-ID: <577CE1DE.6080502@laposte.net> Date: Wed, 6 Jul 2016 12:47:58 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.8.0 MIME-Version: 1.0 In-Reply-To: <577BEABE.2010204@arm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-VR-SrcIP: 83.142.147.193 X-VR-FullState: 0 X-VR-Score: -100 X-VR-Cause-1: gggruggvucftvghtrhhoucdtuddrfeeltddrvdeigddvlecutefuodetggdotefrodftvfcurfhrohhf X-VR-Cause-2: ihhlvgemucfntefrqffuvffgnecuuegrihhlohhuthemucehtddtnecusecvtfgvtghiphhivghnthhs X-VR-Cause-3: ucdlqddutddtmdenucfjughrpefuvfhfhffkffgfgggjtgfgsehtjegrtddtfeehnecuhfhrohhmpefu X-VR-Cause-4: vggsrghsthhirghnucfhrhhirghsuceoshhfkeegsehlrghpohhsthgvrdhnvghtqeenucfkphepkeef X-VR-Cause-5: rddugedvrddugeejrdduleefnecurfgrrhgrmhepmhhouggvpehsmhhtphhouhhtpdhhvghloheplgdu X-VR-Cause-6: jedvrddvjedrtddrvddugegnpdhinhgvthepkeefrddugedvrddugeejrdduleefpdhmrghilhhfrhho X-VR-Cause-7: mhepshhfkeegsehlrghpohhsthgvrdhnvghtpdhrtghpthhtohepmhgrrhgtrdiihihnghhivghrsegr X-VR-Cause-8: rhhmrdgtohhm X-VR-AvState: No X-VR-State: 0 X-VR-State: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Marc, On 07/05/2016 07:13 PM, Marc Zyngier wrote: >>> You really don't need to describe this. The configuration that is >>> applied to your router in entirely under software control, >> >> With "entirely under software control" do you mean this driver's code? > > Yes. Ok. > >> >>> and none of >>> that should appear in the DT. You could decide to mux all the interrupts >>> to a single one, or decide that the 23 first interrupts you discover get >>> their own private line to the GIC and that everything else is muxed. >>> >>> So given that this is completely defined by software, it has no place in >>> DT. >> >> 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. 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? 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? Best regards, Sebastian