From mboxrd@z Thu Jan 1 00:00:00 1970 From: Geert Uytterhoeven Subject: Re: Why isn't IRQ shared for i2c-ocore Date: Fri, 8 May 2015 10:03:14 +0200 Message-ID: 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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: In-Reply-To: <20150508072735.GJ16220@x1> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Lee Jones Cc: York Sun , Julia Lawall , Linux I2C , wolfram-z923LK4zBo2bacvFa/9K2g@public.gmane.org, "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" List-Id: linux-i2c@vger.kernel.org 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-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.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