Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752746AbbEHH1m (ORCPT ); Fri, 8 May 2015 03:27:42 -0400 Received: from mail-wi0-f172.google.com ([209.85.212.172]:38193 "EHLO mail-wi0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751998AbbEHH1j (ORCPT ); Fri, 8 May 2015 03:27:39 -0400 Date: Fri, 8 May 2015 08:27:35 +0100 From: Lee Jones To: Geert Uytterhoeven Cc: York Sun , Julia Lawall , Linux I2C , wolfram@the-dreams.de, "linux-kernel@vger.kernel.org" Subject: Re: Why isn't IRQ shared for i2c-ocore Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1978 Lines: 49 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." -- Lee Jones Linaro STMicroelectronics Landing Team Lead Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog -- 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/