From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matt Porter Subject: Re: [Ksummit-2013-discuss] ARM topic: Is DT on ARM the solution, or is there something better? Date: Tue, 22 Oct 2013 16:42:38 -0400 Message-ID: <20131022204238.GG29341@beef> References: <52644A9E.3060007@wwwdotorg.org> <20131020220839.GT2443@sirena.org.uk> <5264576F.6050307@wwwdotorg.org> <52658EBC.8020800@wwwdotorg.org> <20131022093923.GC15640@ulmo.nvidia.com> <20131022150426.GF29341@beef> <20131022201228.GB8037@mithrandir> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20131022201228.GB8037@mithrandir> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Thierry Reding Cc: Nicolas Pitre , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "ksummit-2013-discuss-cunTk1MwBs98uUxBSJOaYoYkZiVZrdSR2LY78lusg7I@public.gmane.org" , Mark Brown , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , Stephen Warren List-Id: devicetree@vger.kernel.org On Tue, Oct 22, 2013 at 10:12:29PM +0200, Thierry Reding wrote: > On Tue, Oct 22, 2013 at 01:42:48PM -0400, Nicolas Pitre wrote: > > On Tue, 22 Oct 2013, Matt Porter wrote: > > > > > DT has many benefits. It would be great to leverage them as long as it > > > doesn't interfere with the rate of change and willingness to evolve code > > > that's always been the strength of the kernel process. That strength is > > > too valuable to trade away for the "DT as ABI" vision. > > > > Amen. This is the best statement I've read about DT so far. > > > > Having "stable" DT bindings is just a dream. Experience so far is > > showing that this is neither practical nor realistic. > > > > The unstructured free-for-all approach isn't good either. Some > > compromise between the two extremes needs to be found. > > I agree. I think we need an easy way to mark bindings as unstable. One > possible solution that I can think of would be to use some kind of > special marker within the compatible value defined by a binding that > would be used to qualify it as unstable. Perhaps something as simple as > a preceding exclamation mark (!) would do. > > gpio { > compatible = "!foo-gpio"; > }; > > The DT core code could look for that when matching device nodes to the > list of compatible values supported by a driver and output a big warning > message to make users aware of the fact that the binding may change. The > driver could use the same marker in the OF device ID table to make it > clear that it implements an experimental binding. Whenever a binding is > deemed stable we can simply remove the marker from both the driver and > the binding, as well as DTS files. >>From a technical POV this seems nice. What does stable mean at this point? DTBs using the stable binding are forever guaranteed compatibility with newer kernels? We really need to define *exactly* what this implies for future support. More than likely, most bindings will choose to stay experimental/testing indefinitely if stable means a lifetime of ugly backward compatibility hacks. -Matt -- 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