From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Holler Subject: Re: [PATCH 00/21] On-demand device registration Date: Fri, 12 Jun 2015 13:19:28 +0200 Message-ID: <557AC040.40803@ahsoftware.de> References: <1432565608-26036-1-git-send-email-tomeu.vizoso@collabora.com> <5577F533.1060007@ahsoftware.de> <5579602F.1070801@ahsoftware.de> <5579B9E8.9040609@ahsoftware.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Linus Walleij Cc: Tomeu Vizoso , Grant Likely , Mark Rutland , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-fbdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , linux-samsung-soc , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-gpio-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-pm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Dmitry Torokhov , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Rob Herring , "linux-pwm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , DRM PANEL DRIVERS , dmaengine-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Dan Williams , linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: devicetree@vger.kernel.org Am 12.06.2015 um 09:25 schrieb Linus Walleij: > On Thu, Jun 11, 2015 at 6:40 PM, Alexander Holler wrote: >> Am 11.06.2015 um 14:30 schrieb Linus Walleij: > >>> Certainly it is possible to create deadlocks in this scenario, but the >>> scope is not to create an ubreakable system. >> >> IAnd what happens if you run into a deadlock? Do you print "you've lost, try >> changing your kernel config" in some output hidden by a splash-screen? ;) > > Sorry it sounds like a blanket argument, the fact that there are > mutexes in the kernel makes it possible to deadlock, it doesn't > mean we don't use mutexes. Some programming problems are > just like such. I'm not talking about specific deadlocks through mutexes. I'm talking about what happens when driver A needs driver B which needs driver A. How do you recognise and handle that with your instrumented on-demand device initialization? Such a circular dependency might happen by just adding a new fucntion call or by changing the kernel configuration. And with the on-demand stuff, the possibility that the developer introducing this new (maybe optional) call will never hit such a circular dependency is high. So you will end up with a never ending stream of problem reports whenever someone introduced such a circular dependecy without having noticed it. And to come back to specific deadlocks, if you are extending function calls from something former simple to something which might initialize a whole bunch of drivers, needing maybe seconds, I wouldn't say this is a blanket argument, but a real thread. Alexander Holler -- 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