From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lee Jones Subject: Re: Why isn't IRQ shared for i2c-ocore Date: Fri, 8 May 2015 08:27:35 +0100 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-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Geert Uytterhoeven Cc: York Sun , Julia Lawall , Linux I2C , wolfram@the-dreams.de, "linux-kernel@vger.kernel.org" List-Id: linux-i2c@vger.kernel.org On Fri, 08 May 2015, Geert Uytterhoeven wrote: > On Fri, May 8, 2015 at 8:57 AM, Lee Jones wrot= e: > > On Fri, 08 May 2015, Geert Uytterhoeven wrote: > > > >> On Thu, May 7, 2015 at 9:01 AM, Lee Jones w= rote: > >> >> I have a follow up question regarding interrupt. I see many I2C= bus drivers > >> >> request interrupt with flag =3D 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 d= o 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 ma= y 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, yo= u'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? >=20 > All drivers sharing the same interrupt must pass IRQF_SHARED, cfr. th= e > checks in __setup_irq(). >=20 > Traditionally, PC (ISA) drivers didn't share interrupts, as the ISA b= us > prohibited interrupt sharing. > Amiga drivers did. >=20 > New drivers should support IRQ sharing. Precisely, which is why I'm confused by: "However, that's something the driver can't know." --=20 Lee Jones Linaro STMicroelectronics Landing Team Lead Linaro.org =E2=94=82 Open source software for ARM SoCs =46ollow Linaro: Facebook | Twitter | Blog