From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751301AbcFLKA4 (ORCPT ); Sun, 12 Jun 2016 06:00:56 -0400 Received: from foss.arm.com ([217.140.101.70]:46409 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750724AbcFLKAx (ORCPT ); Sun, 12 Jun 2016 06:00:53 -0400 Date: Sun, 12 Jun 2016 11:00:48 +0100 From: Marc Zyngier To: Mason Cc: Sebastian Frias , Thomas Gleixner , LKML , Grygorii Strashko , Mans Rullgard Subject: Re: Using irq-crossbar.c Message-ID: <20160612110048.3dd5ea17@arm.com> In-Reply-To: <575C304F.2070303@free.fr> References: <575ADEBA.2030202@laposte.net> <575AE52E.9020005@arm.com> <575B16BD.50600@free.fr> <20160611105840.69324f8e@arm.com> <575C304F.2070303@free.fr> Organization: ARM Ltd X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.25; arm-unknown-linux-gnueabihf) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 11 Jun 2016 17:37:51 +0200 Mason wrote: > On 11/06/2016 11:58, Marc Zyngier wrote: > > > Mason wrote: > > > >> I think Sebastian is even more baffled by the DT mess > >> (sorry, intricacies) than I am. > > > > This mess is what has saved us from the apocalypse 5 years ago, and > > describing a complex system is not easy (what a surprise...). > > The problem with some Linux APIs is that they're logical and obvious > to people who've been using them for years. For newcomers, it's not > always so obvious. > > In this specific instance, the problem statement seems rather simple, > on the surface. An interrupt controller, X=0..127 lines in, Y=0..23 > lines out (connected to GIC interrupt lines 0..23) and "all" we need > is a way to map Xs to Ys. > > As a first order approximation, it's enough to map all Xs to 0. > And provide a way for the kernel to check the registers containing > the bit-vectors indicating which interrupt(s) fired. If that's what your hardware is, then you are taking the wrong approach. The irq-crossbar driver does not do that at all: it has x inputs and y outputs, but connects exactly *one input to one output*. No multiplexing. And the hierarchical domain infrastructure enforces a similar property: a Linux interrupt is dealt with at each level of the hierarchy without multiplexing: the "irq" is the same, while the "hwirq" varies to reflect the "input pin" for a given interrupt controller. In your particular case, you have an evolved chained interrupt controller, and nothing else. > > > If you just want to apply recipes without understanding the underlying > > constraints, you're in for a lot of pain. > > For example, the IRQ driver for Tango3/4 calls > > irq_find_mapping > generic_handle_irq > irq_desc_get_handler_data > irq_desc_get_chip > chained_irq_enter/chained_irq_exit > irq_setup_alt_chip > irq_get_domain_generic_chip > irq_domain_add_linear > irq_alloc_domain_generic_chips > irq_set_chained_handler > irq_set_handler_data > > Taking irq_find_mapping, I see that there's a short comment in > kernel/irq/irqdomain.c > > /** > * irq_find_mapping() - Find a linux irq from an hw irq number. > * @domain: domain owning this hardware interrupt > * @hwirq: hardware irq number in that domain space > */ > > Is this Doxygen format? Is there a make target to generate > some documentation? Try "make help". > > Other relevant resources, for my own reference: > > https://www.kernel.org/doc/Documentation/IRQ-domain.txt > https://stackoverflow.com/questions/34371352/what-are-linux-irq-domains-why-are-they-needed > https://community.nxp.com/thread/332183 > > Are there other important kernel documentation? > > >> The base file he was referring to is: > >> > >> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/tango4-common.dtsi > > > > I know which file that is, it is mentioned in the diff. I was merely > > trying to point out the glaring mistakes that could be enough for a > > interrupt controller hierarchy to be completely non-functional: > > Only the name of the file was provided, not the path. I was not aware > that you already knew where to find it. I made no claim whatsoever on > the implementation. In fact, I agree with everything Lennart wrote. > > > - Your crossbar doesn't have a #interrupt-cells property. How do you > > expect the interrupt specifiers to be interpreted? > > Why do "fundamental" DT properties start with hash? Because # is a shorthand for "number of". > > > - You've changed the default interrupt controller to be your crossbar. > > Which means that all the sub-nodes are inheriting it. Have you > > checked that this was valid for all of these nodes? > > I'm not sure I follow. All platform interrupts flow into the platform > controller. Maybe other platforms have more complex setups, with > several cascaded controllers? Most embedded platforms do. M. -- Jazz is not dead. It just smells funny.