From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marc Zyngier Subject: Re: [PATCH 3/5] MIPS: lantiq: add an irq_domain and irq_chip for EBU Date: Sat, 03 Aug 2019 10:12:49 +0100 Message-ID: <86o916mx2m.wl-maz@kernel.org> References: <20190727175315.28834-1-martin.blumenstingl@googlemail.com> <20190727175315.28834-4-martin.blumenstingl@googlemail.com> <86y30imq9p.wl-marc.zyngier@arm.com> Mime-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Martin Blumenstingl Cc: tglx@linutronix.de, jason@lakedaemon.net, ralf@linux-mips.org, paul.burton@mips.com, jhogan@kernel.org, robh+dt@kernel.org, linux-mips@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, mark.rutland@arm.com, john@phrozen.org, Hauke Mehrtens List-Id: devicetree@vger.kernel.org Hi Martin, On Thu, 01 Aug 2019 18:42:42 +0100, Martin Blumenstingl wrote: [...] > > > +static void ltq_ebu_irq_handler(struct irq_desc *desc) > > > +{ > > > + struct irq_domain *domain = irq_desc_get_handler_data(desc); > > > + struct irq_chip *irqchip = irq_desc_get_chip(desc); > > > + > > > + chained_irq_enter(irqchip, desc); > > > + > > > + generic_handle_irq(irq_find_mapping(domain, 0)); > > > > Having an irqdomain for a single interrupt is a bit over the top... Is > > that for the convenience of the DT infrastructure? > yes, I did it to get DT support > please let me know if there's a "better" way (preferably with another > driver as example) To be honest, the chained handler is what troubles me the most. You normally would use such a construct if you had a multiplexer. In your case, you have a 1:1 relationship between input and output. It is just that this irqchip allows the trigger to be adapted, which normally calls for a hierarchical implementation. In your case, with only a single interrupt, it doesn't matter much though. > > [...] > > > + irq_create_mapping(domain, 0); > > > > Why do you need to perform this eagerly? I'd expect this interrupt to > > be mapped when it is actually claimed by a driver. > I don't remember why I added it, it may be left-over from copying from > another driver > in v2 I'll try to drop it > > > > + > > > + irq_set_chained_handler_and_data(irq, ltq_ebu_irq_handler, domain); > > > > And there is no HW initialisation whatsoever? I'd expect, at the very > > least, the sole interrupt to be configured as disabled/masked. > I can add that. is there any "best practice" on what I should > initialize (just disable it or also set a "default" mode like > LEVEL_LOW)? Whichever default state makes sense. What you want to avoid is to boot the kernel with a screaming interrupt because some firmware has left it enabled. Thanks, M. -- Jazz is not dead, it just smells funny.