From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Cooper Subject: Re: irqchip heirarchy DT "break" series awareness? Date: Tue, 7 Apr 2015 13:06:38 +0000 Message-ID: <20150407130638.GE7873@io.lakedaemon.net> References: <20150406144647.GC7873@io.lakedaemon.net> <20150407115922.5d4c6233@free-electrons.com> <5523AFAF.6040000@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <5523AFAF.6040000-5wv7dgnIgG8@public.gmane.org> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Marc Zyngier Cc: Thomas Petazzoni , Arnd Bergmann , Olof Johansson , "arm-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org" , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Thomas Gleixner , Linux ARM Kernel List-Id: devicetree@vger.kernel.org On Tue, Apr 07, 2015 at 11:21:35AM +0100, Marc Zyngier wrote: > Hi Thomas, > > On 07/04/15 10:59, Thomas Petazzoni wrote: > > > But the point of the slides stand: even for a piece of hardware as > > well-documented as the GIC, as widely used as the GIC, with as many > > bright and smart engineers looking into it, the community has not been > > able to put out a DT binding that can be kept stable. How can we expect > > such a DT binding stability to occur for undocumented hardware, or > > SoC-specific hardware blocks that are definitely a lot less used than > > the GIC ? > > The problem at hand is not so much the GIC itself, but the fact that > only the GIC was described in DT. The GIC binding is unchanged, but some > additional hardware is now described. Well, if that were the case we wouldn't have a break in DT compatibility. I suppose what we're going for here is "removed GIC binding properties (arm,routable-irqs) that didn't describe hardware". Similar for crossbar and the others that were inappropriately relying on gic_arch_extn implementation to model the (incorrect) hardware description. > If the relationship between the GIC and the shadow interrupt controllers > had been described, we would have avoided breaking the compatibility. I > guess it was too tempting to reuse pre-DT mechanisms and to forget about > this entirely. I'm not sure tempting is the right word. Everyone has known since this project began that we were striving to describe the hardware. I suspect the reason we got to where we are is that people *assumed* the code was describing the hardware, and so wrote bindings reflecting their understanding. iow, we don't have enough hardware engineers reviewing bindings :-P Be that as it may, I'm not trying to rehash the decision. It's clearly the correct thing to do. Otherwise, I wouldn't have pulled it in. What I am trying to do here is make sure a) we have full awareness by everybody not directly involved, and b) make sure I have my ducks in a row if ThomasG/Linus raises questions regarding the pull request. thx, Jason. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html From mboxrd@z Thu Jan 1 00:00:00 1970 From: jason@lakedaemon.net (Jason Cooper) Date: Tue, 7 Apr 2015 13:06:38 +0000 Subject: irqchip heirarchy DT "break" series awareness? In-Reply-To: <5523AFAF.6040000@arm.com> References: <20150406144647.GC7873@io.lakedaemon.net> <20150407115922.5d4c6233@free-electrons.com> <5523AFAF.6040000@arm.com> Message-ID: <20150407130638.GE7873@io.lakedaemon.net> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Apr 07, 2015 at 11:21:35AM +0100, Marc Zyngier wrote: > Hi Thomas, > > On 07/04/15 10:59, Thomas Petazzoni wrote: > > > But the point of the slides stand: even for a piece of hardware as > > well-documented as the GIC, as widely used as the GIC, with as many > > bright and smart engineers looking into it, the community has not been > > able to put out a DT binding that can be kept stable. How can we expect > > such a DT binding stability to occur for undocumented hardware, or > > SoC-specific hardware blocks that are definitely a lot less used than > > the GIC ? > > The problem at hand is not so much the GIC itself, but the fact that > only the GIC was described in DT. The GIC binding is unchanged, but some > additional hardware is now described. Well, if that were the case we wouldn't have a break in DT compatibility. I suppose what we're going for here is "removed GIC binding properties (arm,routable-irqs) that didn't describe hardware". Similar for crossbar and the others that were inappropriately relying on gic_arch_extn implementation to model the (incorrect) hardware description. > If the relationship between the GIC and the shadow interrupt controllers > had been described, we would have avoided breaking the compatibility. I > guess it was too tempting to reuse pre-DT mechanisms and to forget about > this entirely. I'm not sure tempting is the right word. Everyone has known since this project began that we were striving to describe the hardware. I suspect the reason we got to where we are is that people *assumed* the code was describing the hardware, and so wrote bindings reflecting their understanding. iow, we don't have enough hardware engineers reviewing bindings :-P Be that as it may, I'm not trying to rehash the decision. It's clearly the correct thing to do. Otherwise, I wouldn't have pulled it in. What I am trying to do here is make sure a) we have full awareness by everybody not directly involved, and b) make sure I have my ducks in a row if ThomasG/Linus raises questions regarding the pull request. thx, Jason.