From mboxrd@z Thu Jan 1 00:00:00 1970 From: grant.likely@secretlab.ca (Grant Likely) Date: Wed, 19 May 2010 08:21:44 -0600 Subject: Boot interface for device trees on ARM In-Reply-To: <20100519014118.GD2318@shareable.org> References: <201005181054.32325.jeremy.kerr@canonical.com> <201005181324.45701.jeremy.kerr@canonical.com> <20100518084954.GC25892@yookeroo> <20100519002826.GG25892@yookeroo> <20100519014118.GD2318@shareable.org> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, May 18, 2010 at 7:41 PM, Jamie Lokier wrote: > David Gibson wrote: >> On Tue, May 18, 2010 at 08:24:06AM -0400, Nicolas Pitre wrote: >> > On Tue, 18 May 2010, David Gibson wrote: >> > > On Tue, May 18, 2010 at 01:24:43PM +0800, Jeremy Kerr wrote: >> > > > Nicolas Pitre wrote: >> [snip] >> > > The only reason you'd need a subarchitecture number or equivalent is >> > > if you need to do things differently in the very, very early asm boot >> > > code. ?We may need a minimal form of this on PowerPC if we ever >> > > support multiple MMU families in the same kernel binary. >> > >> > Exact. ?For example, on ARM the machine ID is also used to figure out >> > the MMU mapping needed to be able to simply be able to debug the very >> > early assembly boot stage when there isn't even a stack available. While >> > this info is stored in the machine record, it is actually >> > subarchitecture specific and already half-digested for easy usage by >> > that initial MMU setup. ?I just don't want to imagine what the >> > equivalent functionality with DT would look like. >> >> Well, it wouldn't be *that* bad - you'd need a minimal asm-only tree >> walker to find and look up the compatible property. ?Quite possible >> but, yes, fairly awkward. > > I'm not entirely clear, is the DT intended to replace the command line > for saying things like "console=XXX"? It doesn't replace the kernel parameters line, but the kernel parameters line can be passed to the kernel via a property in the /chosen node. Firmware is allowed to modify the DT (ie. to change the kernel parameters) before passing it to the kernel. Cheers, g. -- Grant Likely, B.Sc., P.Eng. Secret Lab Technologies Ltd.