From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robert Schwebel Subject: Re: [RFC] [PATCH] Device Tree on ARM platform Date: Thu, 28 May 2009 01:48:01 +0200 Message-ID: <20090527234801.GP6805@pengutronix.de> References: <1243408083.13460.14.camel@debian-nb> <20090527150527.GK6805@pengutronix.de> <20090527162000.GM6805@pengutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-mnsaURCQ41sdnm+yROfE0A@public.gmane.org Errors-To: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-mnsaURCQ41sdnm+yROfE0A@public.gmane.org To: Grant Likely Cc: devicetree-discuss , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-xIg/pKzrS19vn6HldHNs0ANdhmdF6hFW@public.gmane.org, Janboe Ye , Timur Tabi , rmk-lFZ/pmaqli7XmaaqVzeoHQ@public.gmane.org List-Id: devicetree@vger.kernel.org On Wed, May 27, 2009 at 02:35:11PM -0600, Grant Likely wrote: > > Unfortunately, it is an incomplete data structure regarding to what > > the kernel needs. > > I don't follow your argument. It's a data structure that uniquely > describes your hardware in a way which encourages the most code reuse > possible; but is still independent of kernel internal implementation. > ie. a FDT blob should be usable not just by Linux, but also by BSD or > any of the other OS options. It is not an attempt to eliminate > platform specific code; just to reduce it as much as possible. Weird, > harry, non-standard stuff probably still needs board specific code to > handle. The oftree by design wants to be a complete hardware description. As you mention above, there are cases where you *nevertheless* need ad-hoc information about things *not* encoded into the device tree. This renders the whole concept ad absurdum. You need a machine number again - and if you need that: why not stay with the ARM model, define everything with platform data and avoid the whole thing? Regarding the multi OS argument: I consider it impossible that people agree on all micro details of a hardware decision. Will it really be possible to get a common agreement about let's say Russell's SMSC example between all these people? Remember: if we forget (or don't agree on) one single aspect which a driver developer *needs*, he will have to work around it -> machine number land. My impression is that oftree only works in a perfect world. But we don't have one, so the fundamental design decision is broken. rsc -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |