From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Kerr Subject: Re: Boot interface for device trees on ARM Date: Wed, 9 Jun 2010 12:26:13 +0800 Message-ID: <201006091226.15438.jeremy.kerr@canonical.com> References: <201005181054.32325.jeremy.kerr@canonical.com> <201006050933.06714.jeremy.kerr@canonical.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org Errors-To: devicetree-discuss-bounces+gldd-devicetree-discuss=m.gmane.org-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org To: devicetree-discuss-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org Cc: linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, Nicolas Pitre List-Id: devicetree@vger.kernel.org Hi Nicolas, > > If we're planning to keep the machine IDs around (even if they are now > > per- SoC), I'd like to know what would be left using them. The only > > thing that I can see that we currently use is io_pg_offset for the > > DEBUG_LL builds, and that isn't a convincing case to keep them. > > Why not? Because it's something we can justifiably replace with a single compile-time constant, since it's only for low-level debug. I don't see that as a reason for keeping these machine numbers around if that's all they're used for. However... > Kernel infrastructure backward compatibility means that you need to keep > struct machine_desc instances around. Granted, for the DT case, many of > the members could be NULL or initialized with dummy stubs. But that is > very cheap to keep around, and that allows the same kernel binary to be > able to use both the DT boot and the legacy boot. ... this is a good point; if it helps with the transition, then this is probably a decent reason to keep it in the interface. I'd like to keep my "only use the device tree" value (MACH_TYPE_DT = 0xffffffff) though, so we don't needlessly allocate machine numbers where they aren't actually used. Cheers, Jeremy