From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752838Ab3LRVUx (ORCPT ); Wed, 18 Dec 2013 16:20:53 -0500 Received: from mail-la0-f48.google.com ([209.85.215.48]:54399 "EHLO mail-la0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752567Ab3LRVUu (ORCPT ); Wed, 18 Dec 2013 16:20:50 -0500 Message-ID: <1387401646.31516.14.camel@host5.omatika.ru> Subject: Re: [PATCH v2 00/16] ARM: support for ICP DAS LP-8x4x (with dts) From: Sergei Ianovich To: Arnd Bergmann Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Daniel Mack , Haojian Zhuang Date: Thu, 19 Dec 2013 01:20:46 +0400 In-Reply-To: <201312182210.30544.arnd@arndb.de> References: <1386543229-1542-1-git-send-email-ynvich@gmail.com> <201312182150.39037.arnd@arndb.de> <1387400193.31516.10.camel@host5.omatika.ru> <201312182210.30544.arnd@arndb.de> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.8.5-2+b1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2013-12-18 at 22:10 +0100, Arnd Bergmann wrote: > On Wednesday 18 December 2013, Sergei Ianovich wrote: > > Could we postpone this until someone needs this functionality? > > We have to be sure that any device tree files you write now can remain > compatible with future kernels if we add it later. My reasoning at first > was that this wouldn't work if we had to change the "compatible" string > for the bus node, but after re-thinking it now I believe that it's fine. Great. > You would still be able to boot a kernel with an old dts file on a new > kernel if it just contains a "simple-bus" node here, as long as it doesn't > need any boot-time setup at the bus controller. We can change the dts > file later if we need to add this functionality, which would break booting > old kernels with the new dts files, which isn't much of a problem in > general. It should actually only break old kernels which require new functionally. Otherwise, dts can have compatible = "marvell,pxa-extbus", "simple-bus"; and an older kernel will be happy with "simple-bus". Please correct me if I'm wrong.