Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752705AbbEHIDV (ORCPT ); Fri, 8 May 2015 04:03:21 -0400 Received: from mail-ob0-f179.google.com ([209.85.214.179]:36573 "EHLO mail-ob0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751288AbbEHIDP (ORCPT ); Fri, 8 May 2015 04:03:15 -0400 MIME-Version: 1.0 In-Reply-To: <20150508072735.GJ16220@x1> References: <20150420064231.GE3447@x1> <55352839.70905@freescale.com> <20150420181651.GF3447@x1> <5535460B.2060309@freescale.com> <20150421073534.GK3447@x1> <554A8A8B.1020703@freescale.com> <20150507070149.GB3400@x1> <20150508065747.GG16220@x1> <20150508072735.GJ16220@x1> Date: Fri, 8 May 2015 10:03:14 +0200 X-Google-Sender-Auth: zCSFvAWjpoNvZjD3NOVbFbTkNMM Message-ID: Subject: Re: Why isn't IRQ shared for i2c-ocore From: Geert Uytterhoeven To: Lee Jones Cc: York Sun , Julia Lawall , Linux I2C , wolfram@the-dreams.de, "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2377 Lines: 56 On Fri, May 8, 2015 at 9:27 AM, Lee Jones wrote: > On Fri, 08 May 2015, Geert Uytterhoeven wrote: >> On Fri, May 8, 2015 at 8:57 AM, Lee Jones wrote: >> > On Fri, 08 May 2015, Geert Uytterhoeven wrote: >> >> On Thu, May 7, 2015 at 9:01 AM, Lee Jones wrote: >> >> >> I have a follow up question regarding interrupt. I see many I2C bus drivers >> >> >> request interrupt with flag = 0. Why not using IRQF_SHARED? >> >> > >> >> > Probably because that particular IRQ is only used by the I2C >> >> > Controller. I'm not exactly sure that you're getting at? Why do you >> >> > think it should be shared? You should only flag it as shared if it >> >> > is. >> >> >> >> However, that's something the driver can't know. >> >> Sharing interrupts is an integration property. The same IP core may share its >> >> interrupt on one SoC, and not on another. >> > >> > I guess that would depend on the IP. If this is part of an MFD, you'd >> > know if you only hand a single interrupt line coming into the chip or >> > not. If the IP can be moved around (copy & pasted) into different >> > chips, then yes, that might change. >> > >> > How does one share an interrupt with other drivers if all them don't >> > know the IRQ is shared thought? >> >> All drivers sharing the same interrupt must pass IRQF_SHARED, cfr. the >> checks in __setup_irq(). >> >> Traditionally, PC (ISA) drivers didn't share interrupts, as the ISA bus >> prohibited interrupt sharing. >> Amiga drivers did. >> >> New drivers should support IRQ sharing. > > Precisely, which is why I'm confused by: > > "However, that's something the driver can't know." So better safe than sorry: always use IRQF_SHARED, unless you have a very good reason not to use it. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/