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Date: Thu, 19 Sep 2013 00:31:57 +0200 (CEST) From: Thomas Gleixner <tglx@...utronix.de> To: Santosh Shilimkar <santosh.shilimkar@...com> cc: linus.walleij@...aro.org, Sricharan R <r.sricharan@...com>, LKML <linux-kernel@...r.kernel.org>, devicetree@...r.kernel.org, linux-doc@...r.kernel.org, LAK <linux-arm-kernel@...ts.infradead.org>, linux-omap@...r.kernel.org, Russell King <linux@....linux.org.uk>, Tony Lindgren <tony@...mide.com>, rnayak@...com Subject: Re: [RFC PATCH 1/4] DRIVERS: IRQCHIP: Add crossbar irqchip driver On Wed, 18 Sep 2013, Santosh Shilimkar wrote: > On Friday 13 September 2013 10:55 AM, Santosh Shilimkar wrote: > > On Friday 13 September 2013 10:24 AM, Thomas Gleixner wrote: > > [...] > > >> Before you dig into MSI, lets talk about irq domains first. > >> > >> GIC implements a legacy irq domain, i.e. a linear domain of all > >> possible GIC interrupts with a 1:1 mapping. > >> > >> So why can't you make use of irq domains and have the whole routing > >> business implemented sanely? > >> > >> What's needed is in gic_init_bases(): > >> > >> if (of_property_read(node, "routable_irqs", &nr_routable_irqs) { > >> irq_domain_add_legacy(nr_gic_irqs); > >> } else { > >> irq_domain_add_legacy(nr_per_cpu_irqs); > >> irq_domain_add_linear(nr_routable_irqs); > >> } > >> > >> Now that separate domain has an xlate function which grabs a free GIC > >> irq from a bitmap and returns the hardware irq number in the gic > >> space. The map/unmap callbacks take care of setting up / tearing down > >> the route in the crossbar. > >> > >> Thoughts? > >> > > This sounds pretty good idea. We will explore above option. > > Thanks Thomas. > > > After further looking into this, the irqdomain approach lets us > setup the map only once during the init. This is similar to > the earlier approach of cross-bar driver where at probe time > the router was setup. The whole debate started with the fact > that we shouldn't fix the irq mapping at probe and should > dynamically change the mapping based on [request/free]_irq() > to be able to maximize the use of the IP. Well, that's what irq_of_parse_and_map() resp. irq_create_mapping and irq_dispose_mapping() are for. It requires changes to drivers, but you can't get that thing for free. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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