From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Message-ID: <17451.30312.967754.699319@cargo.ozlabs.ibm.com> Date: Thu, 30 Mar 2006 17:10:48 +1100 From: Paul Mackerras To: Dan Malek Subject: Re: [PATCH] powerpc: Add FSL CPM2 device tree node documentation In-Reply-To: References: <20060328161431.18517.82573.stgit@vitb.ru.mvista.com> Cc: linuxppc-dev List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Dan Malek writes: > I haven't followed the device tree development in detail, but when > looking at this the only question that comes to mind is wondering > what this really does to help me. None of the information provided > here is variable nor configurable .... except I guess for the internal > register base address (IMMR), which for some reason has turned > into a variable which hasn't changed since I did the first kernel port. > About the only thing that is variable, which is the two different bank > addresses of the CPM memory that affects the configuration of > the FCCs in Ethernet mode, isn't reflected here in any way. I don't know much about the CPM or CPM2, so I don't know precisely why these bits have been put in. If the CPM2 is completely unique and is identical across all possible past and future implementations, then indeed there isn't a lot of value in putting details about it in the device tree. Having details in the device tree becomes useful if: * there are variants that have different collections of subdevices, or subdevices at different offsets, or * there are common subdevices between CPM and CPM2 (or future CPM* devices), potentially with subtle variations in offset, method of enabling, etc., or * there are subdevices in CPM/CPM2 which match some common device (e.g. a 16550 uart) for which a generic driver can be used with some appropriate configuration. As I say, I don't know if these points apply to CPM/CPM2 specifically. Paul.