From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932286AbdC1LGR (ORCPT ); Tue, 28 Mar 2017 07:06:17 -0400 Received: from gate.crashing.org ([63.228.1.57]:37991 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932145AbdC1LGO (ORCPT ); Tue, 28 Mar 2017 07:06:14 -0400 Message-ID: <1490692375.3177.119.camel@kernel.crashing.org> Subject: Re: [PATCH v6 2/5] irqchip/aspeed-i2c-ic: Add I2C IRQ controller for Aspeed From: Benjamin Herrenschmidt To: Marc Zyngier , Brendan Higgins , wsa@the-dreams.de, robh+dt@kernel.org, mark.rutland@arm.com, tglx@linutronix.de, jason@lakedaemon.net, joel@jms.id.au, vz@mleia.com, mouse@mayc.ru, clg@kaod.org Cc: linux-i2c@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, openbmc@lists.ozlabs.org Date: Tue, 28 Mar 2017 20:12:55 +1100 In-Reply-To: <49a13bbc-aec3-a349-4323-3c8d2728c62f@arm.com> References: <20170328051226.21677-1-brendanhiggins@google.com> <20170328051226.21677-3-brendanhiggins@google.com> <49a13bbc-aec3-a349-4323-3c8d2728c62f@arm.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6 (3.22.6-1.fc25) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2017-03-28 at 09:32 +0100, Marc Zyngier wrote: > I'm a bit concerned by this. It means that you can't even mask an > interrupt. Is that really what you intend to do? Or all that the HW can > do? If you cannot mask an interrupt, you're at the mercy of a screaming > device... This is not really an interrupt controller. It's a "summary" register that reflects the state of the 14 i2c controller interrupts. This approach does have the advantage of providing separate counters in /proc/interrupts which is rather nice, but it does have overhead. On those shittly little ARMv9 400Mhz cores it can be significant. I would personally have some kind of trick to register a single interrupt handler that calls directly the handlers of the respective i2c busses via a simple indirection for speed, maybe adding my custom sysfs or debugfs statistics. But that's just me trying to suck the last cycle out of the bloody thing ;-) Cheers, Ben.